OMC Omnicom Group Inc

As filed with the U.S. Securities and Exchange Commission on January 29, 2025

Registration No. 333-284358

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

AMENDMENT NO. 1 TO

FORM S-4

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

Omnicom Group Inc.

(Exact Name of Registrant as Specified in Its Charter)

280 Park Avenue, New York, NY 10017

(212) 415-3600

(Address, including Zip Code, and Telephone Number, Including Area Code, of Registrant’s Principal Executive Offices)

Louis F. Januzzi

Senior Vice President, General Counsel and Secretary

Omnicom Group Inc.

280 Park Avenue, New York, NY 10017

(212) 415-3600

(Name, Address, including Zip Code, and Telephone Number, including Area Code, of Agent for Service)

With a copy to:

Approximate date of commencement of proposed sale of the securities to the public: As soon as practicable after this registration statement is declared effective.

If the securities being registered on this form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, please check the following box. ☐

If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act of 1933, as amended (the “Securities Act”), check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

If this form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐

If applicable, place an X in the box to designate the appropriate rule provision relied upon in conducting this transaction:

Exchange Act Rule 13e-4(i) (Cross-Border Issuer Tender Offer) ☐

Exchange Act Rule 14d-1(d) (Cross-Border Third-Party Tender Offer) ☐

The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act or until the Registration Statement shall become effective on such date as the U.S. Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

Holders of IPG common stock (the “IPG stockholders”) as of the close of business on January 27, 2025, the record date, are invited to virtually attend a special meeting of IPG stockholders (the “IPG special meeting”) on March 18, 2025, at 9:00 a.m. Eastern Time, via live webcast at www.virtualshareholdermeeting.com/IPG2025SM. At the IPG special meeting, IPG stockholders will be asked to consider and vote upon: (1) a proposal to adopt the merger agreement (the “IPG merger proposal”), (2) a non-binding advisory proposal to approve certain compensation that may be paid or become payable to IPG’s named executive officers that is based on or otherwise relates to the merger (the “IPG compensation proposal”) and (3) a proposal to approve one or more adjournments of the IPG special meeting to a later date or time, if necessary or appropriate, to permit the solicitation of additional votes or proxies if there are not sufficient votes to approve the IPG merger proposal (the “IPG adjournment proposal”).

The Omnicom board of directors has unanimously determined that the transactions contemplated by the merger agreement, including the merger and the issuance of shares of Omnicom common stock in connection with the merger, are advisable, fair to, and in the best interests of, Omnicom and its stockholders; has unanimously approved, adopted and declared advisable the merger agreement and the transactions contemplated by the merger agreement, including the merger and the issuance of shares of Omnicom common stock in connection with the merger; and unanimously recommends that Omnicom stockholders vote “FOR” the Omnicom issuance proposal and “FOR” the Omnicom adjournment proposal.

The IPG board of directors has unanimously determined that the terms of the merger agreement and the transactions contemplated by the merger agreement, including the merger, are advisable, fair to, and in the best interests of, IPG and its stockholders; has unanimously approved, authorized and adopted the merger agreement and the transactions contemplated by the merger agreement, including the merger; and unanimously recommends that IPG stockholders vote “FOR” the IPG merger proposal, “FOR” the IPG compensation proposal and “FOR” the IPG adjournment proposal.

Omnicom and IPG cannot complete the merger unless, among other things, both Omnicom stockholders approve the Omnicom issuance proposal and IPG stockholders approve the IPG merger proposal.

Your vote is very important. To ensure your representation at your company’s special meeting, complete and return the applicable enclosed proxy card or submit your proxy by phone or the Internet. Please vote promptly, whether or not you expect to virtually attend your company’s special meeting. Submitting a proxy now will not prevent you from being able to vote at your company’s special meeting.

The joint proxy statement/prospectus accompanying this notice is also being delivered to IPG stockholders as Omnicom’s prospectus for its offering of shares of Omnicom common stock in connection with the merger.

The obligations of Omnicom and IPG to complete the merger are subject to the satisfaction or waiver of the conditions set forth in the merger agreement, a copy of which is included as part of the accompanying joint proxy statement/prospectus. The joint proxy statement/prospectus provides you with detailed information about the merger. It also contains or references information about Omnicom and IPG and certain related matters. You are encouraged to read the joint proxy statement/prospectus carefully and in its entirety. In particular, you should carefully read the section entitled “Risk Factors” beginning on page 32 of the joint proxy statement/prospectus for a discussion of risks you should consider in evaluating the merger and the issuance of shares of Omnicom common stock in connection with the merger.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be issued under the accompanying joint proxy statement/prospectus or passed upon the adequacy or accuracy of the disclosure in this document. Any representation to the contrary is a criminal offense.

The joint proxy statement/prospectus is dated [ ], 2025 and is first being mailed to stockholders of Omnicom and IPG on or about [ ], 2025.

280 Park Avenue

New York, New York 10017

NOTICE OF THE SPECIAL MEETING OF STOCKHOLDERS

OF OMNICOM GROUP INC.

TO BE HELD VIRTUALLY VIA LIVE WEBCAST ON MARCH 18, 2025

Dear Stockholder,

You are cordially invited to attend a virtual-only special meeting of stockholders (the “Omnicom special meeting”) of Omnicom Group Inc. (“Omnicom”) to be held on March 18, 2025, at 9:00 a.m. Eastern Time, via live webcast at www.virtualshareholdermeeting.com/OMC2025SM (the “Omnicom special meeting website”) to consider and vote on the following:

The Omnicom special meeting will be held in a virtual meeting format only, via live webcast, and there will not be a physical meeting location. You will be able to attend the Omnicom special meeting online and vote your shares and submit questions electronically at the meeting by visiting the Omnicom special meeting website.

Stockholder approval of the Omnicom issuance proposal is required to complete the transactions contemplated by the merger agreement, including the merger between Merger Sub and IPG (the “merger”). Holders of Omnicom common stock (“Omnicom stockholders”) will also be asked to approve the Omnicom adjournment proposal. Omnicom will transact no other business at the Omnicom special meeting, except such business as may be properly brought before the Omnicom special meeting or any adjournment thereof by or at the direction of the board of directors of Omnicom (the “Omnicom board”) in accordance with the By-laws of Omnicom. The record date for the Omnicom special meeting has been set as January 27, 2025. Only Omnicom stockholders of record as of the close of business on such record date are entitled to receive notice of, and to vote at, the Omnicom special meeting via the Omnicom special meeting website or any adjournment or postponement of the Omnicom special meeting. For additional information regarding the Omnicom special meeting, see the section entitled “Special Meeting of Omnicom Stockholders” beginning on page 49 of the joint proxy statement/prospectus accompanying this notice.

The Omnicom board unanimously recommends that Omnicom stockholders vote “FOR” the Omnicom issuance proposal and “FOR” the Omnicom adjournment proposal.

The accompanying joint proxy statement/prospectus describes the Omnicom proposals in more detail. Please refer to the attached document, including the merger agreement and all other annexes and any documents incorporated by reference, for further information with respect to the business to be transacted at the Omnicom special meeting. You are encouraged to read the entire document carefully before voting. A summary of the merger agreement is included in the accompanying joint proxy statement/prospectus in the section entitled “The Merger Agreement” and a copy of the merger agreement is attached as Annex A to the accompanying joint proxy statement/prospectus, each of which is incorporated by reference into this notice to the same extent as if fully set forth herein. In addition, see the section entitled “Risk Factors” beginning on page 32 of the joint proxy statement/prospectus accompanying this notice for an explanation of the material risks associated with the merger and the other transactions contemplated by the merger agreement.

PLEASE VOTE AS PROMPTLY AS POSSIBLE, WHETHER OR NOT YOU PLAN TO ATTEND THE OMNICOM SPECIAL MEETING VIA THE OMNICOM SPECIAL MEETING WEBSITE. IF YOU LATER DESIRE TO REVOKE OR CHANGE YOUR PROXY FOR ANY REASON, YOU MAY DO SO IN THE MANNER DESCRIBED IN THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS. FOR FURTHER INFORMATION CONCERNING THE PROPOSALS BEING VOTED UPON, USE OF THE PROXY AND OTHER RELATED MATTERS, YOU ARE URGED TO READ THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS.

If you have any questions concerning the Omnicom proposals, the merger or the accompanying joint proxy statement/prospectus, would like additional copies or need help voting your shares of Omnicom common stock, please contact Omnicom’s proxy solicitor:

Innisfree M&A Incorporated

501 Madison Avenue, 20th Floor

New York, NY 10022

Stockholders may call toll free: (877) 717-3898

Banks and Brokers may call collect: (212) 750-5833

BY ORDER OF THE BOARD OF DIRECTORS,

Louis F. Januzzi

Senior Vice President, General Counsel and Secretary

Omnicom Group Inc.

909 Third Avenue

New York, New York 10022

NOTICE OF THE SPECIAL MEETING OF STOCKHOLDERS OF

THE INTERPUBLIC GROUP OF COMPANIES, INC.

TO BE HELD VIRTUALLY VIA LIVE WEBCAST ON MARCH 18, 2025

Dear Stockholder,

You are cordially invited to attend a virtual-only special meeting of stockholders (the “IPG special meeting”) of The Interpublic Group of Companies, Inc. (“IPG”) to be held on March 18, 2025, at 9:00 a.m. Eastern Time, via live webcast at www.virtualshareholdermeeting.com/IPG2025SM (the “IPG special meeting website”), to consider and vote on the following:

The IPG special meeting will be held in a virtual meeting format only, via live webcast, and there will not be a physical meeting location. You will be able to attend the IPG special meeting online and vote your shares and submit questions electronically at the meeting by visiting the IPG special meeting website.

Stockholder approval of the IPG merger proposal is required to complete the merger, as contemplated by the merger agreement. Holders of IPG common stock (“IPG stockholders”) will also be asked to approve the IPG compensation proposal and the IPG adjournment proposal. IPG will transact no other business at the IPG special meeting except such business as may be properly brought before the IPG special meeting or any adjournment thereof by or at the direction of the board of directors of IPG (the “IPG board”) in accordance with the Amended and Restated By-laws of IPG. The record date for the IPG special meeting has been set as January 27, 2025. Only IPG stockholders of record as of the close of business on such record date are entitled to receive notice of, and to vote at, the IPG special meeting via the IPG special meeting website or any adjournment or postponement of the IPG special meeting. For additional information regarding the IPG special meeting, see the section entitled “Special Meeting of IPG Stockholders” beginning on page 57 of the joint proxy statement/prospectus accompanying this notice.

The IPG board unanimously recommends that IPG stockholders vote “FOR” the IPG merger proposal, “FOR” the IPG compensation proposal, and “FOR” the IPG adjournment proposal.

The accompanying joint proxy statement/prospectus describes the IPG proposals in more detail. Please refer to the attached document, including the merger agreement and all other annexes and any documents incorporated by reference, for further information with respect to the business to be transacted at the IPG special meeting. You

are encouraged to read the entire document carefully before voting. A summary of the merger agreement is included in the accompanying joint proxy statement/prospectus in the section entitled “The Merger Agreement” and a copy of the merger agreement is attached as Annex A to the accompanying joint proxy statement/ prospectus, each of which are incorporated by reference into this notice to the same extent as if fully set forth herein. In addition, see the section entitled “Risk Factors” beginning on page 32 of the joint proxy statement/ prospectus accompanying this notice for an explanation of the material risks associated with the merger and the other transactions contemplated by the merger agreement.

PLEASE VOTE AS PROMPTLY AS POSSIBLE, WHETHER OR NOT YOU PLAN TO ATTEND THE IPG SPECIAL MEETING VIA THE IPG SPECIAL MEETING WEBSITE. IF YOU LATER DESIRE TO REVOKE OR CHANGE YOUR PROXY FOR ANY REASON, YOU MAY DO SO IN THE MANNER DESCRIBED IN THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS. FOR FURTHER INFORMATION CONCERNING THE PROPOSALS BEING VOTED UPON, USE OF THE PROXY AND OTHER RELATED MATTERS, YOU ARE URGED TO READ THE ACCOMPANYING JOINT PROXY STATEMENT/PROSPECTUS.

If you have any questions concerning the IPG proposals, the merger or the accompanying joint proxy statement/prospectus, would like additional copies or need help voting your shares of IPG common stock, please contact IPG’s proxy solicitor:

D.F. King & Co., Inc.

48 Wall Street, 22nd Floor

New York, NY 10005

Banks and Brokers Call Collect: (212) 434-0035

All Others Call Toll-Free: (800) 669-5550

Email:IPG@dfking.com

BY ORDER OF THE BOARD OF DIRECTORS,

Robert Dobson

Senior Vice President, Associate General Counsel and Secretary

The Interpublic Group of Companies, Inc.

REFERENCES TO ADDITIONAL INFORMATION

This joint proxy statement/prospectus incorporates by reference important business and financial information about Omnicom Group Inc. (“Omnicom”) and The Interpublic Group of Companies, Inc. (“IPG”) from other documents that are not included in or delivered with this joint proxy statement/prospectus, including documents that Omnicom and IPG have filed with the U.S. Securities and Exchange Commission (“SEC”). For a listing of documents incorporated by reference herein, see the section entitled “Where You Can Find More Information.” This information is available for you to review free of charge at the public reference room of the SEC located at 100 F Street, N.E., Washington, DC 20549, and through the SEC’s website at www.sec.gov.

You may request copies of this joint proxy statement/prospectus and any of the documents incorporated by reference herein or other information concerning Omnicom or IPG, without charge, upon written or oral request to the applicable company’s principal executive offices. The respective addresses and phone numbers of such principal executive offices are listed below.

To obtain timely delivery of these documents before the Omnicom special meeting (as defined in the section entitled “Questions and Answers about the Merger and the Special Meetings”), Omnicom stockholders must request the information no later than March 11, 2025 (which is five business days before the date of the Omnicom special meeting).

To obtain timely delivery of these documents before the IPG special meeting (as defined in the section entitled “Questions and Answers about the Merger and the Special Meetings”), IPG stockholders must request the information no later than March 11, 2025 (which is five business days before the date of the IPG special meeting).

In addition, if you have questions about the merger or this joint proxy statement/prospectus, would like additional copies of this joint proxy statement/prospectus or need to obtain proxy cards or other information related to the proxy solicitation, contact Innisfree M&A Incorporated, the proxy solicitor for Omnicom, toll-free at (877) 717-3898, or for banks and brokers, collect at (212) 750-5833, or D.F. King & Co., Inc., the proxy solicitor for IPG, toll-free at (800) 669-5550, or for brokers and banks, collect at (212) 434-0035. You will not be charged for any of these documents that you request.

ABOUT THIS JOINT PROXY STATEMENT/PROSPECTUS

This document, which forms part of a registration statement on Form S-4 filed with the SEC by Omnicom (File No. 333-284358), constitutes a prospectus of Omnicom under Section 5 of the Securities Act of 1933, as amended (the “Securities Act”), with respect to the shares of common stock of Omnicom, par value $0.15 per share (“Omnicom common stock”), to be issued to IPG stockholders pursuant to the Agreement and Plan of Merger, dated as of December 8, 2024 (as it may be amended from time to time, the “merger agreement”), among Omnicom, EXT Subsidiary Inc. (“Merger Sub”) and IPG.

This document also constitutes a notice of meeting and proxy statement of each of Omnicom and IPG under Section 14(a) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”).

Omnicom has supplied all information contained or incorporated by reference herein relating to Omnicom, and IPG has supplied all information contained or incorporated by reference herein relating to IPG. Omnicom and IPG have both contributed to the information relating to the merger agreement contained in this joint proxy statement/prospectus.

Neither Omnicom nor IPG has authorized anyone to provide any information or to make any representations other than those contained in or incorporated by reference in this joint proxy statement/prospectus in connection with any vote, the giving or withholding of any proxy or any investment decision in connection with the merger agreement. Omnicom and IPG take no responsibility for, and can provide no assurance as to the reliability of, any other information that others may give you. This joint proxy statement/prospectus is dated [ ], 2025, and you should not assume that the information contained in this joint proxy statement/prospectus is accurate as of any date other than such date unless otherwise specifically provided herein. Further, you should not assume that the information incorporated by reference in this joint proxy statement/prospectus is accurate as of any date other than the date of the incorporated document. Neither the mailing of this joint proxy statement/prospectus to Omnicom or IPG stockholders nor the issuance by Omnicom of shares of Omnicom common stock pursuant to the merger agreement will create any implication to the contrary.

All currency amounts referenced in this joint proxy statement/prospectus are in U.S. dollars unless otherwise indicated.

TABLE OF CONTENTS

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QUESTIONS AND ANSWERS ABOUT THE MERGER AND THE SPECIAL MEETINGS

The following are some questions that you, as an Omnicom stockholder or an IPG stockholder, as applicable, may have regarding the merger, the issuance of shares of Omnicom common stock to IPG stockholders in connection with the merger, and the other matters being considered at the Omnicom special meeting and the IPG special meeting, and the answers to those questions. Omnicom and IPG urge you to carefully read the remainder of this joint proxy statement/prospectus because the information in this section does not provide all of the information that might be important to you with respect to the merger, the issuance of shares of Omnicom common stock in connection with the merger, and the other matters being considered at the Omnicom special meeting and the IPG special meeting. Additional important information is also contained in the annexes to, and the documents incorporated by reference in, this document.

The merger agreement, which governs the terms of the merger, is attached to this joint proxy statement/prospectus as Annex A.

In order to consummate the merger, among other things:

Omnicom is holding a virtual special meeting of its stockholders (the “Omnicom special meeting”) to obtain approval of the Omnicom issuance proposal. Omnicom stockholders will also be asked to vote on a proposal to approve one or more adjournments of the Omnicom special meeting to a later date or time, if necessary or appropriate, to permit the solicitation of additional votes or proxies if there are not sufficient votes to approve the Omnicom issuance proposal (the “Omnicom adjournment proposal” and, together with the Omnicom issuance proposal, the “Omnicom proposals”).

IPG is holding a virtual special meeting of its stockholders (the “IPG special meeting”) to obtain approval of the IPG merger proposal. IPG stockholders will also be asked to vote on (i) a non-binding advisory proposal to approve certain compensation that may be paid or become payable to IPG’s named executive officers that is based on or otherwise relates to the merger (the “IPG compensation proposal”) and (ii) a proposal to approve one or more adjournments of the IPG special meeting to a later date or time, if necessary or appropriate, to permit the solicitation of additional votes or proxies if there are not sufficient votes to approve the IPG merger proposal (the “IPG adjournment proposal” and, together with the IPG merger proposal and the IPG compensation proposal, the “IPG proposals”).

Your vote is very important. We encourage you to submit a proxy to have your shares of Omnicom common stock or IPG common stock voted as soon as possible.

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IPG. The IPG special meeting will be held virtually via live webcast on March 18, 2025, at 9:00 a.m. Eastern Time. IPG stockholders will be able to attend the IPG special meeting online and vote their shares and submit questions electronically during the meeting by visiting www.virtualshareholdermeeting.com/IPG2025SM (the “IPG special meeting website”). Because the IPG special meeting is completely virtual and being conducted via live webcast, IPG stockholders will not be able to attend the meeting in person.

IPG. The IPG stockholders are being asked to consider and vote on:

See the sections entitled “The Merger—Consideration to IPG Stockholders” beginning on page 65 and “The Merger Agreement—Effect of the Merger on Capital Stock; Merger Consideration” beginning on page 129.

Effective as of the effective time of the merger, each outstanding IPG restricted stock unit (each, an “IPG RSU”) and each outstanding IPG performance stock unit (each, an “IPG PSU”) will be assumed by Omnicom and converted into a cash award equal to the fair market value of the shares of IPG common stock underlying such award based on the closing price of such shares of IPG common stock on the last day prior to the closing on which shares of IPG common stock are traded on the NYSE. For this purpose, the number of shares of IPG common stock subject to an IPG PSU will be determined based on either (i) the target level of performance, or (ii) if the performance period in respect of such IPG PSU ended on or prior to the effective time, the greater of actual and target level performance. Each IPG RSU and IPG PSU, as converted to a cash award, will, except as otherwise set forth in this paragraph, continue to be subject to the same

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terms and conditions as applied to such award immediately prior to the effective time (including any double-trigger vesting protections, forfeiture terms and terms relating to dividend or dividend equivalent rights, but excluding any performance-based vesting conditions for the IPG PSUs). In addition, all IPG RSUs held by non-employee members of the board of directors of IPG (the “IPG board”) will be fully vested immediately prior to the effective time.

IPG RSAs

Effective as of the effective time of the merger, each outstanding IPG restricted stock award (each an “IPG RSA”) will be assumed by Omnicom and converted into an Omnicom restricted stock award (an “Omnicom RSA”) covering a number of shares of Omnicom common stock equal to the product of (A) the number of shares of IPG common stock subject to such IPG RSA immediately prior to the effective time multiplied by (B) 0.344. Each such Omnicom RSA will, except as otherwise set forth in this paragraph, continue to be subject to the same terms and conditions as applied to such IPG RSA immediately prior to the effective time (including any double-trigger vesting protections, forfeiture terms and terms relating to dividend or dividend equivalent rights). In addition, all IPG RSAs held by non-employee members of the IPG board will be fully vested immediately prior to the effective time and will be treated as any other fully-vested share of IPG common stock in the merger (as described in the section entitled “The Merger Agreement—Effect of the Merger on Capital Stock; Merger Consideration”).

IPG Cash Awards

Each award granted under the IPG Restricted Cash Plan and each performance cash award granted under an IPG Stock Plan (as defined below, and together, the “IPG cash awards”) outstanding immediately prior to the effective time of the merger, will be assumed by Omnicom and will continue to be subject to the same terms and conditions as applied to such IPG cash award immediately prior to the effective time (including any requirement for continued service with IPG or its affiliates, any double-trigger vesting protections and forfeiture terms but excluding any performance-based vesting conditions), provided that the payment opportunity in respect of any IPG cash award that is performance-based will equal the target amount of such award as in effect immediately prior to the effective time or, if the performance period in respect of such award ended on or prior to the effective time, the greater of the target amount and the amount determined based on actual performance.

IPG Stock Options

Effective as of the effective time of the merger, each outstanding and unexercised option to purchase IPG common stock (each, an “IPG stock option”) will be assumed by Omnicom and converted into an option to purchase a number of shares of Omnicom common stock equal to the product of (A) the number of shares of IPG common stock subject to such IPG stock option immediately prior to the effective time multiplied by (B) 0.344 (an “Omnicom stock option”). The Omnicom stock option will have an exercise price per share of Omnicom common stock equal to the quotient obtained by dividing (x) the exercise price per share of such IPG stock option by (y) 0.344. Each Omnicom stock option will, except as otherwise set forth in this paragraph, continue to be subject to the same terms and conditions as applied to the IPG stock option immediately prior to the effective time (including any double-trigger vesting protections, forfeiture and exercisability terms and terms relating to dividend or dividend equivalent rights).

ESPP

Prior to the effective time of the merger, IPG will terminate the purchase period then in effect for the employee stock purchase plan (the “ESPP”) and will cause the exercise of each outstanding right to purchase shares of IPG common stock under the ESPP, in each case, no later than the business day immediately prior to the effective time of the merger. Such exercise will be effectuated by applying the

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funds credited in each ESPP participant’s payroll withholding account to the purchase of whole shares of IPG common stock in accordance with the terms of the ESPP, and such shares of IPG common stock will be entitled to the merger consideration (as described in the section entitled “The Merger Agreement—Effect of the Merger on Capital Stock; Merger Consideration”). Any remaining funds will be returned to the participant as promptly as practicable following the purchase of IPG common stock. Immediately prior to and effective as of the effective time of the merger, subject to consummation of the merger, IPG will terminate the ESPP.

Assumption of IPG Stock Plans

At the effective time of the merger, Omnicom will assume the IPG 2019 Performance Incentive Plan, the IPG 2014 Performance Incentive Plan and any predecessor plan, in each case, as amended and/or restated (together, and excluding the ESPP, the “IPG Stock Plans”), and will continue to maintain such assumed plans (each, as may be amended or terminated from time to time in accordance with its terms).

For additional information regarding the treatment of IPG equity awards, see the section entitled “The Merger Agreement—Treatment of IPG Equity Awards in the Merger” beginning on page 130.

Omnicom. The merger cannot be completed unless the Omnicom issuance proposal is approved by the affirmative vote of the holders of a majority of the shares voting on the proposal. Only Omnicom stockholders as of the close of business on the record date are entitled to vote at the Omnicom special meeting. The board of directors of Omnicom (the “Omnicom board”) unanimously recommends that Omnicom stockholders vote “FOR” the Omnicom issuance proposal and “FOR” the Omnicom adjournment proposal.

IPG. The merger cannot be completed unless the IPG merger proposal is approved by the affirmative vote of a majority of the outstanding shares of IPG common stock entitled to vote on such proposal. Only IPG stockholders as of the close of business on the record date are entitled to vote at the IPG special meeting. The IPG board unanimously recommends that IPG stockholders vote “FOR” the IPG merger proposal, “FOR” the IPG compensation proposal and “FOR” the IPG adjournment proposal.

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The Omnicom adjournment proposal. When a quorum is present, approval of the Omnicom adjournment proposal requires the affirmative vote of the holders of a majority of the shares voting on the proposal. Abstentions, broker non-votes or any failure by an Omnicom stockholder to vote (e.g., by not submitting a proxy and not voting at the Omnicom special meeting) will have no effect on the outcome of the Omnicom adjournment proposal when a quorum is present. When a quorum is not present, approval of the Omnicom adjournment proposal requires the affirmative vote of the holders of a majority of the shares entitled to vote at the meeting who are present or represented by proxy. Abstentions will have the same effect as a vote “AGAINST” the adjournment proposal, while broker non-votes or any failure by an Omnicom stockholder to vote (e.g., by not submitting a proxy and not voting at the Omnicom special meeting) will have no effect on the outcome of the Omnicom adjournment proposal when a quorum is not present. Approval of the Omnicom adjournment proposal is not a condition to the completion of the merger.

The IPG compensation proposal. Approval of the IPG compensation proposal, which is a non-binding advisory proposal, requires the affirmative vote of a majority of the shares of IPG common stock present via the IPG special meeting website or by proxy at the IPG special meeting and entitled to vote on such proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal. Broker non-votes, or any failure by an IPG stockholder to vote (e.g., by not submitting a proxy and not voting at the IPG special meeting) will have no effect on the outcome of the IPG compensation proposal. As an advisory vote, this proposal is not binding on IPG or the IPG board or Omnicom or the Omnicom board, and approval of this proposal is not a condition to the completion of the merger.

The IPG adjournment proposal. Approval of the IPG adjournment proposal requires the affirmative vote of a majority of the shares of IPG common stock present via the IPG special meeting website or by proxy at the IPG special meeting and entitled to vote on such proposal, whether or not a quorum is present. Abstentions will have the same effect as a vote “AGAINST” the proposal. Broker non-votes and any failure by an IPG stockholder to vote (e.g., by not submitting a proxy and not voting at the IPG special meeting) will have no effect on the outcome of the IPG adjournment proposal. Approval of this proposal is not a condition to the completion of the merger.

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Under the current New York Stock Exchange (“NYSE”) rules, brokers, banks or other nominees do not have discretionary authority to vote on any of the Omnicom proposals at the Omnicom special meeting or any of the IPG proposals at the IPG special meeting. Because all of the proposals for consideration at the Omnicom special meeting and IPG special meeting are “non-routine,” it is not expected that there will be any broker non-votes at the Omnicom special meeting or the IPG special meeting. However, if there are any broker non-votes, they will have (i) no effect on the outcome of the Omnicom issuance proposal or the Omnicom adjournment proposal and (ii) the same effect as a vote “AGAINST” the IPG merger proposal and no effect on the outcome of the IPG compensation proposal and the IPG adjournment proposal.

IPG. Help and technical support for accessing and participating in the virtual meeting will be available by following the instructions on the virtual meeting website (www.virtualshareholdermeeting.com/IPG2025SM). If you encounter any difficulties accessing the IPG special meeting during the check-in or meeting time, please call the technical support number that will be posted on the virtual meeting website login page (www.virtualshareholdermeeting.com/IPG2025SM). Please give yourself sufficient time to log in and ensure you can hear the streaming audio before the meeting starts.

IPG. The IPG board unanimously recommends that IPG stockholders vote “FOR” the IPG merger proposal, “FOR” the IPG compensation proposal and “FOR” the IPG adjournment proposal. For additional information regarding how the IPG board recommends that IPG stockholders vote, see the section entitled “The Merger—Recommendation of the IPG Board of Directors and Reasons for the Merger” beginning on page 93.

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The IPG board was aware of and considered these differing interests, to the extent such interests existed at the time, among other matters, in evaluating and negotiating the merger agreement and the merger and in unanimously recommending that IPG stockholders approve the IPG proposals. For additional information, see the section entitled “The Merger—Interests of IPG Directors and Executive Officers in the Merger” beginning on page 120.

Omnicom special meeting. The Omnicom board has fixed January 27, 2025 as the record date for the Omnicom special meeting. All holders of record of shares of Omnicom common stock as of the close of business on the record date are entitled to receive notice of, and to vote at, the Omnicom special meeting via the Omnicom special meeting website or by proxy, provided that those shares remain outstanding on the date of the Omnicom special meeting. As of the record date, there were 196,480,662 shares of Omnicom common stock outstanding. Attendance at the Omnicom special meeting via the Omnicom special meeting website is not required to vote. Instructions on how to vote your shares without virtually attending the Omnicom special meeting are provided in this section below.

IPG special meeting. The IPG board has fixed January 27, 2025 as the record date for the IPG special meeting. All holders of record of shares of IPG common stock as of the close of business on the record date are entitled to receive notice of, and to vote at, the IPG special meeting via the IPG special meeting website or by proxy, provided that those shares remain outstanding on the date of the IPG special meeting. As of the record date, there were 372,645,940 shares of IPG common stock outstanding. Attendance at the IPG special meeting via the IPG special meeting website is not required to vote. Instructions on how to vote your shares without virtually attending the IPG special meeting are provided in this section below.

IPG stockholders. Each IPG stockholder of record is entitled to one vote for each share of IPG common stock held of record by such stockholder as of the close of business on the record date.

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Quorum for IPG special meeting. The presence, via the IPG special meeting website or by proxy, of the holders of a majority of the outstanding shares of IPG common stock entitled to vote at the IPG special meeting will constitute a quorum for the transaction of business. If you submit a properly executed proxy card, even if you vote “against” the IPG proposals or “abstain” from voting on the IPG proposals, your shares of IPG common stock will be counted for purposes of calculating whether a quorum is present. Because all of the proposals for consideration at the IPG special meeting are “non-routine” under applicable NYSE rules, brokers, banks and other nominees do not have discretionary authority to vote on any of the IPG proposals and will not be able to vote on any of the IPG proposals absent instructions from the beneficial owner. Accordingly, it is not expected that there will be any broker non-votes at the IPG special meeting. Broker non-votes, if any, will not be considered present and entitled to vote on any of the IPG proposals for the purpose of determining the presence of a quorum with respect to the vote thereon.

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IPG. Shares of IPG common stock held directly in your name as the stockholder of record as of the close of business on January 27, 2025, the record date, may be voted at the IPG special meeting via the IPG special meeting website. Please note that attendance alone at the IPG special meeting via the IPG special meeting website will not cause the voting of your shares; you must affirmatively vote by proxy or via the IPG special meeting website. If you choose to attend the IPG special meeting and vote your shares via the IPG special meeting website, you will need the 16-digit control number included on your proxy card. If you are a beneficial owner of IPG common stock but not the stockholder of record of such shares of IPG common stock, and your broker, bank or other nominee has not provided you with a 16-digit control number on the voting instruction form it furnishes you, you will need to obtain a control number from your broker, bank or other nominee holder of record giving you the right to vote the shares at the IPG special meeting.

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IPG. If you are a stockholder of record of IPG common stock as of the close of business on January 27, 2025, the record date, you can vote by proxy, phone, the Internet or mail by following the instructions provided in the enclosed proxy card. Please note that if you are a beneficial owner, you may vote by submitting voting instructions to your broker, bank or other nominee, or otherwise by following instructions provided by your broker, bank or other nominee. Phone and Internet voting may be available to beneficial owners. Please refer to the voting instruction form provided by your broker, bank or other nominee.

IPG. If your shares of IPG common stock are registered directly in your name with IPG’s transfer agent, Computershare Trust Company, N.A., you are considered the stockholder of record with respect to those shares, and access to proxy materials is being provided directly to you. If your shares are held in a stock brokerage account or by a broker, bank or other nominee, then you are considered the beneficial owner of those shares, which are considered to be held in “street name.” Access to proxy materials is being provided to you by your broker, bank or other nominee who is considered the stockholder of record with respect to those shares.

Direct holders (stockholders of record). For shares of Omnicom common stock and/or IPG common stock held directly, complete, sign, date and return each proxy card (or cast your vote by phone or the Internet as

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provided on each proxy card) or otherwise follow the voting instructions provided in this joint proxy statement/prospectus in order to ensure that all of your shares of Omnicom common stock and/or IPG common stock are voted.

Shares in “street name.” For shares of Omnicom common stock and/or IPG common stock held in “street name” through a broker, bank or other nominee, follow the instructions provided by your broker, bank or other nominee to vote your shares.

IPG. If you sign, date and return your proxy and do not indicate how you want your shares of IPG common stock to be voted, then your shares of IPG common stock will be voted “FOR” the IPG merger proposal, “FOR” the IPG compensation proposal and “FOR” the IPG adjournment proposal.

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Please note that your attendance at the meeting via the Omnicom special meeting website will not alone serve to revoke your previously submitted proxy; instead, you must vote your shares via the Omnicom special meeting website in order to do so.

If you are a beneficial owner of Omnicom common stock as of the close of business on the record date, you must follow the instructions of your broker, bank or other nominee to revoke or change your voting instructions.

IPG. Yes. If you are a stockholder of record of IPG common stock as of the close of business on the record date, whether you vote by phone, the Internet or mail, you can change or revoke your proxy before it is voted at the IPG special meeting in one of the following ways:

If you are a beneficial owner of IPG common stock as of the close of business on the record date, you must follow the instructions of your broker, bank or other nominee to revoke or change your voting instructions.

IPG stockholders. IPG stockholders may vote against the IPG merger proposal if they do not support the merger. Because shares of IPG common stock are listed on the NYSE and IPG stockholders are not required to receive consideration other than shares of Omnicom common stock, which are listed on the NYSE, and cash in lieu of fractional shares in the merger, IPG stockholders are not entitled to exercise appraisal rights under Delaware law in connection with the merger.

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IPG stockholders. The record date for IPG stockholders entitled to vote at the IPG special meeting is earlier than the date of the IPG special meeting. If you transfer your shares of IPG common stock after the record date but before the IPG special meeting, you will, unless special arrangements are made, retain your right to vote at the IPG special meeting but will have transferred the right to receive the merger consideration to the person to whom you transferred your shares of IPG common stock.

If the merger qualifies as a reorganization, then U.S. holders (as defined in the section entitled “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 155) of shares of IPG common stock generally will not recognize any gain or loss for U.S. federal income tax purposes upon receipt of Omnicom common stock in exchange for IPG common stock in the merger (other than gain or loss, if any, with respect to any cash received in lieu of a fractional share of Omnicom common stock). The material U.S. federal income tax consequences of the merger are discussed in more detail in the section entitled “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 155. The discussion of the material U.S. federal income tax consequences contained in this joint proxy statement/prospectus is intended to provide only a general discussion and is not a complete analysis or description of all potential U.S. federal income tax consequences of the merger that may vary with, or are dependent on, individual circumstances. In addition, it does not address the effects of any foreign, state or local tax laws or any U.S. federal tax laws other than U.S. federal income tax laws.

TAX MATTERS ARE COMPLICATED AND THE TAX CONSEQUENCES OF THE MERGER WILL DEPEND ON THE FACTS OF YOUR OWN SITUATION. YOU SHOULD CONSULT YOUR OWN TAX ADVISOR AS TO THE SPECIFIC TAX CONSEQUENCES OF THE MERGER TO YOU IN YOUR PARTICULAR CIRCUMSTANCES.

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More information may be found in “The Merger Agreement— Conditions to the Completion of the Merger” beginning on page 149.

If you are a holder of book-entry shares representing eligible shares of IPG common stock (“IPG book-entry shares”) that are held through the Depository Trust Company (“DTC”), the exchange agent will transmit to DTC or its nominees, as soon as reasonably practicable on or after the closing date, the merger consideration and cash in lieu of any fractional shares of Omnicom common stock that DTC has the right to receive pursuant to the merger agreement.

If you are a holder of record of IPG book-entry shares that are not held through DTC, the exchange agent will deliver to you, as soon as reasonably practicable after the effective time of the merger, (1) a notice advising you of the effectiveness of the merger, (2) a statement reflecting the aggregate whole number of shares of Omnicom common stock (which will be in uncertificated book-entry form) that you have a right to receive pursuant to the merger agreement and (3) a check in the amount equal to the cash payable in lieu of any fractional shares of Omnicom common stock.

No interest will be paid or accrued on any amount payable for shares of IPG common stock eligible to receive the merger consideration pursuant to the merger agreement.

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For additional information on the exchange of IPG common stock for the merger consideration, see the section entitled “The Merger Agreement—Payment for Securities; Exchange.”

IPG. IPG has retained D.F. King & Co., Inc. (“D.F. King”) to assist in the solicitation process. IPG will pay D.F. King a fee of approximately $100,000, as well as reasonable and customary documented expenses. IPG also has agreed to indemnify D.F. King against various liabilities and expenses that relate to or arise out of its solicitation of proxies (subject to certain exceptions).

IPG has also elected to institute householding.

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Innisfree M&A Incorporated

501 Madison Avenue, 20th Floor

New York, NY 10022

Stockholders may call toll free: (877) 717-3898

Banks and Brokers may call collect: (212) 750-5833

IPG stockholders. If you have questions about the IPG special meeting or the information contained in this joint proxy statement/prospectus, or desire additional copies of this joint proxy statement/prospectus or additional proxies, contact IPG’s proxy solicitor:

D.F. King & Co., Inc.

48 Wall Street, 22nd Floor

New York, NY 10005

Banks and Brokers Call Collect: (212) 434-0035

All Others Call Toll-Free: (800) 669-5550

Email: IPG@dfking.com

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RISK FACTORS

In addition to the other information contained in or incorporated by reference herein, including the matters addressed in the section entitled “Cautionary Statement Regarding Forward-Looking Statements,” you should carefully consider the following risks before deciding how to vote. You should also consider the other information in this joint proxy statement/prospectus and the other documents incorporated by reference herein, particularly the risk factors contained in Omnicom’s and IPG’s Annual Reports on Form 10-K and Quarterly Reports on Form 10-Q. For additional information, see the section entitled “Where You Can Find More Information.” In addition to the risks set forth below or referenced above, new risks may emerge from time to time and it is not possible to predict all risk factors, nor can Omnicom or IPG assess the impact of all factors on the merger and the combined company following the merger or the extent to which any factor or combination of factors may cause actual results to differ materially from those contained in or implied by any forward-looking statements.

Risks Relating to the Merger

Because the exchange ratio is fixed and because the market prices of shares of Omnicom common stock and IPG common stock will fluctuate, IPG stockholders cannot be certain of the market value of the merger consideration they will receive in the merger or the difference between the market value of the merger consideration they will receive in the merger and the market value of their shares of IPG common stock immediately prior to the merger.

At the time the merger is completed, each issued and outstanding share of IPG common stock will be converted into the right to receive the merger consideration of 0.344 shares of Omnicom common stock, together with cash paid in lieu of the issuance of any fractional shares of Omnicom common stock. The exchange ratio for the merger consideration is fixed, and there will be no adjustment to the merger consideration, regardless of whether the market price of Omnicom common stock or IPG common stock changes prior to the completion of the merger. The market prices of Omnicom common stock and IPG common stock have fluctuated since the date on which Omnicom and IPG announced they entered into the merger agreement and will continue to fluctuate from the date of this joint proxy statement/prospectus to the date of the Omnicom special meeting and the IPG special meeting, and the date on which IPG stockholders actually receive the merger consideration. The market prices of Omnicom common stock and IPG common stock will fluctuate during these periods as a result of a variety of factors, including general market and economic conditions, changes in Omnicom’s and IPG’s respective businesses, operations and prospects, market assessments of Omnicom’s and IPG’s businesses, operations and prospects and of the likelihood that the merger will be completed and regulatory considerations. Such factors are difficult to predict and in many cases are beyond the control of Omnicom and IPG. Consequently, at the time IPG stockholders must decide whether to approve the IPG proposals, they will not know the market value of the merger consideration they will receive in the merger, which will depend on the market value of the shares of Omnicom common stock as of the effective time of merger.

In addition, IPG stockholders will not know the difference between the market value of the merger consideration they will receive in the merger and the market value of IPG common stock immediately prior to the merger, which will depend on the market value of Omnicom common stock and IPG common stock as of the effective time of the merger. Unless otherwise mutually agreed between Omnicom and IPG, the completion of the merger will take place within two business days after the satisfaction or waiver of the conditions to the completion of the merger (other than any such conditions which by their nature cannot be satisfied until the closing date, which will be required to be so satisfied or waived in accordance with the merger agreement on the closing date). IPG stockholders should obtain current stock price quotations for shares of Omnicom common stock and IPG common stock before voting their shares of IPG common stock. For additional information about the merger consideration, see the sections entitled “The Merger—Consideration to IPG Stockholders” and “The Merger Agreement—Effect of the Merger on Capital Stock; Merger Consideration.”

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Omnicom stockholders and IPG stockholders, in each case as of immediately prior to the merger, will have reduced ownership in the combined company and less influence over management.

Based on the number of issued and outstanding shares of IPG common stock as of January 27, 2025 and the number of IPG equity awards currently estimated to be payable in shares of Omnicom common stock in connection with the merger, Omnicom anticipates issuing up to approximately 129,462,731 shares of Omnicom common stock pursuant to the merger agreement. The actual number of shares of Omnicom common stock to be issued pursuant to the merger agreement will be determined at the completion of the merger based on the number of shares of IPG common stock outstanding immediately prior to such time and the number of issued and outstanding IPG equity awards payable in shares of Omnicom common stock in connection with the merger.

Immediately after the completion of the merger, it is expected that Omnicom stockholders as of immediately prior to the merger will own approximately 60.6%, and IPG stockholders as of immediately prior to the merger will own approximately 39.4% of the issued and outstanding shares of Omnicom common stock (in each case based on fully diluted shares outstanding of each company), which will continue to trade on the NYSE under the ticker symbol “OMC” following the completion of the merger. As a result, current Omnicom stockholders and current IPG stockholders will have less influence on the management and policies of the combined company than they currently have on the management and policies of Omnicom and IPG, respectively.

The merger may not be completed, and the merger agreement may be terminated in accordance with its terms.

The merger is subject to a number of conditions that must be satisfied or waived prior to the completion of the merger, which are described in the section entitled “The Merger Agreement—Conditions to the Completion of the Merger.” These conditions to the completion of the merger may not be satisfied or waived in a timely manner or at all, and, accordingly, the merger may be delayed or may not be completed.

In addition, if the merger is not completed by December 8, 2025 (which date may be extended to June 8, 2026 in certain circumstances), either Omnicom or IPG may choose not to proceed with the merger by terminating the merger agreement, and the parties can mutually decide to terminate the merger agreement at any time, before or after stockholder approval. In addition, Omnicom and IPG may elect to terminate the merger agreement in certain other circumstances as further detailed in the section entitled “The Merger Agreement—Termination.”

The merger agreement limits Omnicom’s ability and IPG’s ability to pursue alternatives to the merger, may discourage other companies from trying to acquire a significant interest in Omnicom’s or IPG’s common stock or assets and, in specified circumstances, could require Omnicom or IPG to pay the other party a termination fee.

The merger agreement contains provisions that may discourage a third party from submitting a proposal for a competing transaction, including the acquisition of a significant interest in Omnicom’s or IPG’s common stock or assets. These provisions include a general prohibition on Omnicom and IPG from soliciting or, subject to certain exceptions relating to the exercise of fiduciary duties by the Omnicom board or the IPG board, entering into discussions with any third party regarding any such competing proposal. Further, even if the Omnicom board or the IPG board withholds, withdraws, qualifies or modifies its recommendation to stockholders with respect to the Omnicom issuance proposal, in the case of the Omnicom board, or the IPG merger proposal, in the case of the IPG board, unless the merger agreement has been terminated in accordance with its terms, each of Omnicom and IPG will still be required to submit the Omnicom issuance proposal, in the case of the Omnicom board, and the IPG merger proposal, in the case of the IPG board, to a vote by the Omnicom stockholders and IPG stockholders, respectively. The merger agreement further provides that (a) if IPG terminates the merger agreement because, prior to Omnicom’s receipt of the approval of the Omnicom issuance proposal, the Omnicom board effects an Omnicom adverse recommendation change (as defined below) or because Omnicom commits a willful and material breach of its non-solicitation obligations, Omnicom will be required to pay IPG $676 million, and (b) if Omnicom terminates

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the merger agreement because, prior to IPG’s receipt of the approval of the IPG merger proposal, the IPG board effects an IPG adverse recommendation change (as defined below) or because IPG commits a willful and material breach of its non-solicitation obligations, IPG will be required to pay Omnicom $439 million. In addition, if the merger agreement is terminated due to either party’s failure to obtain stockholder approval, and at such time, the other party has obtained stockholder approval, Omnicom or IPG, as applicable, may be required to reimburse the other party for its expenses incurred in connection with the transaction in an amount not to exceed $25 million. For additional information, see the sections entitled “The Merger Agreement—No Solicitation; Changes of Recommendation” and “The Merger Agreement—Termination.”

Failure to complete the merger could negatively impact the price of shares of Omnicom common stock and the price of shares of IPG common stock, as well as Omnicom’s and IPG’s respective businesses and financial results.

The merger agreement contains a number of conditions that must be satisfied or waived prior to the completion of the merger, which are described in the section entitled “The Merger Agreement—Conditions to the Completion of the Merger.” There can be no assurance that all of the conditions to the completion of the merger will be satisfied or waived. If these conditions are not satisfied or waived, Omnicom and IPG will be unable to complete the merger.

If the merger is not completed for any reason, including the failure to receive the required approvals of the Omnicom stockholders or the IPG stockholders, Omnicom’s and IPG’s respective businesses and financial results may be adversely affected and, without realizing any of the benefits of having completed the merger, Omnicom and IPG would be subject to a number of risks, including:

In addition to the above risks, if the merger agreement is terminated and either party’s board seeks an alternative transaction, the holders of such party’s common stock cannot be certain that such party will be able to find a party willing to engage in a transaction on more attractive terms than the merger. If the merger agreement is terminated under specified circumstances, either Omnicom or IPG may be required to pay the other party a termination fee or other termination-related payment. For a description of these circumstances, see the section entitled “The Merger Agreement—Termination.”

Directors and executive officers of each party have interests in the merger that may be different from, or in addition to, the interests of Omnicom stockholders and IPG stockholders generally.

In considering the recommendation of (i) the Omnicom board that Omnicom stockholders vote in favor of the proposals on the agenda for the Omnicom special meeting or (ii) the IPG board that IPG stockholders vote in

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favor of the proposals on the agenda for the IPG special meeting, as applicable, Omnicom stockholders and IPG stockholders should be aware of and take into account the fact that certain Omnicom and IPG directors and executive officers have interests in the merger that may be different from, or in addition to, the interests of Omnicom stockholders and IPG stockholders generally. The interests of IPG’s directors and officers include, among other things, single-trigger accelerated vesting of director equity awards, double-trigger severance and vesting protection for IPG’s executive officers for qualifying terminations during the two-year period following the consummation of the merger and rights to continuing indemnification and directors’ and officers’ liability insurance, each as further described in the section entitled “The Merger—Interests of IPG Directors and Executive Officers in the Merger.” Other interests include the continued employment of certain executive officers of Omnicom and IPG following the merger and the continued positions of certain directors of Omnicom and IPG as directors of the combined company. The Omnicom board and the IPG board were aware of and considered the interests of their respective directors and officers, among other matters, in evaluating the terms and structure, and overseeing the negotiation of the merger, in approving the merger agreement and the transactions contemplated thereby, including the merger, and the recommendation of (i) the Omnicom board that Omnicom stockholders vote in favor of the proposals on the agenda for the Omnicom special meeting and (ii) the IPG board that IPG stockholders vote in favor of the proposals on the agenda for the IPG special meeting.

The unaudited pro forma condensed combined financial statements and unaudited prospective financial information included in this joint proxy statement/prospectus are preliminary and future results of Omnicom or IPG may differ, possibly materially.

The unaudited pro forma condensed combined financial statements and unaudited prospective financial information contained in this joint proxy statement/prospectus are based on a variety of adjustments, assumptions and preliminary estimates and may not be indicative of the financial position or results of operations of the combined company following the merger for several reasons. Specifically, the unaudited pro forma condensed combined financial statements do not reflect the effect of any integration costs or any changes in Omnicom’s debt to capitalization ratio following the completion of the merger. In addition, the unaudited pro forma condensed combined financial statements have been prepared with the assumption that Omnicom will be identified as the acquirer under accounting principles generally accepted in the United States of America (“GAAP”) and reflect adjustments based upon preliminary estimates of the fair value of assets to be acquired and liabilities to be assumed. For additional information, see the section entitled “Unaudited Pro Forma Condensed Combined Financial Statements.” In addition, the merger and post-merger integration process may give rise to unexpected liabilities and costs, including costs associated with the defense and resolution of transaction-related litigation or other claims. Unexpected delays in completing the merger or in connection with the post-merger integration process may significantly increase the related costs and expenses incurred by the combined company. The actual financial position, financial performance and results of operations of the combined company following the merger may not be consistent with, or evident from, the unaudited pro forma condensed combined financial statements or prospective financial information included in this joint proxy statement/prospectus. In addition, the assumptions, including those regarding the future operating and financial performance of the combined company, used in preparing the unaudited pro forma condensed combined financial statements and prospective financial information included in this joint proxy statement/prospectus may not prove to be accurate and may be affected by other factors. See “Risk Factors—Risks Relating to the Combined Company Following Completion of the Merger— The market price of Omnicom common stock after the completion of the merger may be affected by factors different from those that historically have affected or currently affect Omnicom common stock.” Any potential decline in the financial condition or results of operations of the combined company may cause significant variations in the price of the common stock of the combined company. For more information, see the unaudited pro forma condensed combined financial statements and the unaudited prospective financial information contained in this joint proxy statement/prospectus.

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The opinions of Omnicom’s and IPG’s respective financial advisors do not reflect changes in circumstances between the signing of the merger agreement and the completion of the merger.

Omnicom and IPG have received opinions from their respective financial advisors in connection with the signing of the merger agreement, but have not obtained updated opinions from their respective financial advisors as of the date of this joint proxy statement/prospectus. Changes in the operations and prospects of Omnicom or IPG, general market and economic conditions and other factors that are beyond the control of Omnicom or IPG, and on which Omnicom’s and IPG’s financial advisors’ opinions were based, may significantly alter the value of Omnicom or IPG or the prices of the shares of Omnicom common stock or IPG common stock by the time the merger is completed. The opinions do not speak as of the time the merger will be completed or as of any date other than the date of the opinions. Because Omnicom and IPG do not currently anticipate asking their respective financial advisors to update their opinions, the opinions will not address the fairness of the exchange ratio from a financial point of view at the time the merger is completed. The Omnicom board’s recommendation that Omnicom stockholders vote in favor of the proposals on the agenda for the Omnicom special meeting and the IPG board’s recommendation that IPG stockholders vote in favor of the proposals on the agenda for the IPG special meeting, however, are made as of the date of this joint proxy statement/prospectus.

For a description of the opinions that Omnicom and IPG received from their respective financial advisors, see the sections entitled “The Merger—Opinion of PJT Partners LP, Omnicom’s Financial Advisor” and “The Merger—Opinion of Morgan Stanley & Co. LLC, IPG’s Financial Advisor.” A copy of the opinion of PJT Partners, Omnicom’s financial advisor, is attached as Annex B to this joint proxy statement/prospectus, and a copy of the opinion of Morgan Stanley, IPG’s financial advisor, is attached as Annex C to this joint proxy statement/prospectus, and each is incorporated by reference herein in its entirety.

The financial forecasts relating to Omnicom and IPG included in this joint proxy/prospectus are based on various estimates and assumptions that may not be realized, which may adversely affect the market price of common stock of the combined company following the closing of the merger.

This joint proxy statement/prospectus includes certain financial forecasts considered by Omnicom and IPG in the evaluation of the merger. None of the financial forecasts prepared by Omnicom or IPG were prepared with a view towards public disclosure or compliance with the published guidelines of the SEC, GAAP or the guidelines established by the American Institute of Certified Public Accountants or any other regulatory or professional body for the preparation and presentation of financial forecasts. These forecasts are inherently based on various estimates and assumptions that are subject to the judgment of those preparing them. These forecasts are also subject to significant economic, competitive, industry and other uncertainties and contingencies, all of which are difficult or impossible to predict and many of which are beyond the control of Omnicom and IPG. Important factors that may affect the actual results of Omnicom and IPG and cause the internal financial forecasts to not be achieved include risks and uncertainties relating to Omnicom’s and IPG’s businesses, industry performance, the regulatory environment, general business and economic conditions and other factors referred to under the section entitled “Cautionary Statement Regarding Forward-Looking Statements.” In view of these uncertainties, the inclusion of financial forecasts in this joint proxy statement/prospectus is not and should not be viewed as a representation that the forecasted results will necessarily reflect actual future results.

In addition, the financial forecasts also reflect assumptions that are subject to change and do not reflect revised prospects for Omnicom’s and IPG’s businesses, changes in general business or economic conditions or any other transaction or event that has occurred or that may occur and that was not anticipated at the time the financial forecasts were prepared. Further, any forward-looking statement speaks only as of the date on which it is made, and neither Omnicom nor IPG undertakes any obligation, other than as required by applicable law, to update the financial estimates to reflect events or circumstances after the dates as of which the financial estimates were prepared or to reflect the occurrence of anticipated or unanticipated events or circumstances. In addition, since such financial forecasts cover multiple years, and the underlying information by its nature becomes less predictive with each successive year, there can be no assurance that Omnicom’s, IPG’s or the combined company’s financial condition or results of operations will be consistent with those set forth in such forecasts.

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Uncertainties associated with the merger may cause a loss of Omnicom’s and IPG’s management personnel and other key employees, which could adversely affect the business and operations of the combined company following the merger.

Each of Omnicom and IPG depends on the experience and industry knowledge of its officers and other key employees to execute its business plans. The success of the combined company after the merger will depend, in part, on its ability to retain key management personnel and other key employees. Current and prospective employees of Omnicom and IPG may experience uncertainty about their roles within the combined company following the merger or other concerns regarding the timing and completion of the merger or the operations of the combined company following the merger, any of which may have an adverse effect on Omnicom’s and IPG’s ability to retain or attract key management and other key personnel. If Omnicom or IPG are unable to retain personnel, including Omnicom’s or IPG’s key management, who are critical to the future operations of the companies, Omnicom and IPG could face disruptions in their operations, loss of existing clients, loss of key information, expertise or know-how and unanticipated additional recruitment and training costs. In addition, the loss of Omnicom’s and IPG’s key personnel could diminish the anticipated benefits of the merger. No assurance can be given that the combined company, following the merger, will be able to retain or attract Omnicom’s and IPG’s key management personnel and other key employees to the same extent that Omnicom and IPG have previously been able to retain or attract personnel.

Omnicom’s and IPG’s business relationships may be subject to disruption due to uncertainty associated with the merger, which could have a material effect on Omnicom’s and IPG’s business, financial condition, cash flows and results of operations or those of the combined company following the merger.

Parties with which Omnicom or IPG do business may experience uncertainty associated with the merger, including with respect to current or future business relationships with Omnicom or IPG following the merger. Omnicom’s and IPG’s business relationships may be subject to disruption as clients, vendors, landlords, joint venture participants and other third parties with whom they do business may attempt to delay or defer entering into new business relationships, negotiate changes in existing business relationships or consider entering into business relationships with parties other than Omnicom or IPG. These disruptions could have a material and adverse effect on Omnicom’s and IPG’s business, financial condition, cash flows and results of operations, regardless of whether the merger is completed, as well as a material and adverse effect on the combined company’s ability to realize the expected cost savings, operating synergies and other benefits of the merger. The risk, and adverse effects, of any disruption could be exacerbated by a delay in completion of the merger or termination of the merger agreement.

Completion of the merger may trigger change-in-control or other provisions in certain agreements to which IPG is a party.

The completion of the merger may trigger change-in-control or other provisions in certain agreements to which IPG is a party. If IPG is unable to negotiate waivers of those provisions, the counterparties may exercise their rights and remedies under the applicable agreements, including in some instances potentially terminating the agreements or seeking monetary damages. Even if IPG is able to negotiate waivers, the counterparties may require a fee for such waivers or seek to renegotiate the agreements on terms less favorable to the combined company.

In addition, in connection with the merger, Omnicom and IPG both have acknowledged and agreed that the merger will constitute a “change in control,” “change of control,” or term of similar import under each applicable IPG plan as described in more detail in the section entitled “The Merger—Interests of IPG Directors and Executive Officers in the Merger.”

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Completion of the merger may trigger other defaults under the debt agreements to which IPG and/or Omnicom are a party.

In addition to a change in control referenced above, the completion of the merger may trigger other defaults or events of default in certain agreements to which IPG or Omnicom is a party. Omnicom’s credit facilities include certain restrictions on the existence of indebtedness by subsidiaries of Omnicom, including indebtedness of subsidiaries existing at the time of the acquisition of such subsidiaries, which restrict Omnicom’s ability to incur or assume indebtedness of IPG. IPG and Omnicom intend to seek amendments to, or a refinancing of, their respective credit facilities, or a new credit facility, to permit the consummation of the merger and the assumption of the senior notes of IPG and to address the revolving credit needs, any commercial paper programs and other financing arrangements of the combined company on a go-forward basis. There can be no assurance that Omnicom and IPG will be able to refinance the credit facilities on favorable terms for the combined company or at all. If IPG and Omnicom are unable to refinance the existing credit facilities or negotiate waivers to such provisions, the counterparties may exercise their rights and remedies under the applicable agreements, including in some instances potentially terminating the agreements or seeking monetary damages. Even if IPG and Omnicom are able to refinance the credit facilities or negotiate waivers to the applicable provisions, the counterparties may require a fee for such waivers or seek to renegotiate such agreements on terms less favorable to the combined company.

Omnicom or IPG may waive one or more of the closing conditions without re-soliciting stockholder approval.

Omnicom or IPG may determine to waive, in whole or part, one or more of the conditions to closing the merger prior to Omnicom or IPG, as the case may be, being obligated to consummate the merger. Each of Omnicom and IPG currently expects to evaluate the materiality of any waiver and its effect on its respective stockholders in light of the facts and circumstances at the time of any such waiver in order to determine whether any amendment of this joint proxy statement/prospectus or any re-solicitation of proxies is required in light of such waiver. Any determination whether to waive any condition to the merger or to re-solicit stockholder approval or amend or supplement this joint proxy statement/prospectus as a result of any such waiver will be made by Omnicom or IPG at the time of such waiver based on the facts and circumstances as they exist at that time.

The merger agreement subjects Omnicom and IPG to restrictions on their respective business activities prior to the effective time of the merger.

The merger agreement restricts Omnicom and IPG from entering into certain corporate transactions and taking other specified actions without the consent of the other party, and generally requires each party to continue its operations in the ordinary course through the completion of the merger. These restrictions could be in place for an extended period of time if completion of the merger is delayed and could prevent Omnicom and IPG from pursuing attractive business opportunities that may arise prior to the completion of the merger. For a description of the restrictive covenants to which Omnicom and IPG are subject, see the section entitled “The Merger Agreement—Interim Operations of IPG and Omnicom Pending the Merger.”

Omnicom and IPG are expected to incur significant costs in connection with the merger and integration of the two companies, which may be in excess of those anticipated by Omnicom or IPG.

Omnicom and IPG have incurred and expects to continue to incur a number of non-recurring costs associated with negotiating and completing the merger and combining the operations of the two companies. These costs have been, and will continue to be, substantial. The substantial majority of non-recurring costs will consist of transaction costs related to the merger and include, among others, fees paid to financial, legal and accounting advisors, filing fees, employee retention and other employment-related costs, and debt restructuring costs. Many of these costs will be borne by Omnicom or IPG even if the merger is not completed.

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Omnicom and IPG will also incur transaction costs related to formulating and implementing integration plans, including facilities, systems and service contract consolidation costs and employment-related costs. Omnicom and IPG will continue to assess the magnitude of these costs, and additional unanticipated costs may be incurred in connection with the merger and the integration of the two companies’ businesses. Although Omnicom and IPG each expect that the elimination of duplicative costs, as well as the realization of other synergies related to the integration of the businesses, should allow the combined company to offset integration-related costs over time, this net benefit may not be achieved in the near term, or at all. For additional information, see the risk factor entitled “—The failure to integrate Omnicom’s and IPG’s businesses and operations successfully in the expected time frame may adversely affect the combined company’s business and results of operations” below. The costs described above, as well as other unanticipated costs and expenses, could adversely affect the financial condition, cash flows and results of operations of the combined company following the completion of the merger.

If the merger does not qualify as a “reorganization” within the meaning of Section 368(a) of the Code, IPG stockholders may be required to pay substantial U.S. federal income taxes.

The merger is intended to qualify as a “reorganization” within the meaning of Section 368(a) of the Code, and IPG, Omnicom, and Merger Sub have covenanted to use reasonable best efforts to (i) take or cause to be taken, and not knowingly fail to take, any action necessary for the merger to qualify as a “reorganization” within the meaning of Section 368(a) of the Code, and (ii) cause IPG to receive an opinion from IPG’s external counsel, dated as of the closing date, to the effect that, on the basis of facts, representations and assumptions set forth or referred to in such opinion, the merger will qualify as a “reorganization” within the meaning of Section 368(a) of the Code. The foregoing opinion of counsel will be based on, among other things, certain representations made by Omnicom and IPG and certain assumptions, all of which must be consistent with the state of facts existing at the time of the merger. If any of these representations and assumptions are, or become, inaccurate or incomplete, such opinion may be invalid, and the conclusions reached therein could be jeopardized. In addition, such opinion of counsel is not free from doubt. An opinion of counsel represents counsel’s best legal judgment and is not binding on the IRS or the courts, which may not agree with the conclusions set forth in such opinion. If the merger does not qualify as a “reorganization” within the meaning of Section 368(a) of the Code, a U.S. holder (as defined in the section entitled “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 155) of IPG common stock would generally recognize capital gain or loss on the exchange of its IPG common stock for Omnicom common stock and cash in lieu of fractional shares of Omnicom common stock pursuant to the merger. For more information, see the section titled “Material U.S. Federal Income Tax Consequences of the Merger.”

Litigation relating to the merger, if any, could result in an injunction preventing the completion of the merger and/or substantial costs to Omnicom and IPG.

Securities class action lawsuits and derivative lawsuits are often brought against public companies that have entered into acquisition, merger or other business combination agreements like the merger agreement. Even if such a lawsuit is without merit, defending against these claims can result in substantial costs and require management time and resources. An adverse judgment could result in monetary damages, which could have a negative impact on Omnicom’s and IPG’s respective liquidity and financial condition. Lawsuits that may be brought against Omnicom, IPG or their respective directors could also seek, among other things, injunctive relief or other equitable relief, including a request to rescind parts of the merger agreement already implemented and to otherwise enjoin the parties from consummating the merger. One of the conditions to the closing of the merger is that no Law or Order (each as defined in the merger agreement) is promulgated, entered, enforced, enacted or issued by any governmental entity of competent jurisdiction in which either Omnicom and its subsidiaries (taken as a whole) or IPG and its subsidiaries (taken as a whole) have material assets or material business operations, which prohibits, restrains or makes illegal the consummation of the merger. Consequently, if a plaintiff is successful in obtaining an injunction prohibiting completion of the merger, that injunction may delay or prevent the merger from being completed within the expected timeframe or at all, which may adversely affect

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Omnicom’s and IPG’s respective businesses, financial condition, cash flows and results of operations. In addition, either Omnicom or IPG may terminate the merger agreement if any Law or Order has been promulgated, entered, enforced, enacted or issued by any governmental entity of competent jurisdiction in which either Omnicom and its subsidiaries (taken as a whole) or IPG and its subsidiaries (taken as a whole) have material assets or material business operations, which is in effect and permanently prohibits, restrains, enjoins or makes illegal the consummation of the merger, so long as Omnicom’s or Merger Sub’s (in the case of a termination by Omnicom) or IPG’s (in the case of a termination by IPG) material breach of any of its obligations under the merger agreement has not been the primary cause of, or resulted in, the enactment or issuance of such Law or Order.

There can be no assurance that any of the defendants would be successful in the outcome of any potential future lawsuits. The defense or settlement of any lawsuit or claim that remains unresolved at the time the merger is completed may adversely affect the combined company’s business, financial condition, cash flows and results of operations.

Omnicom and IPG stockholders will not be entitled to appraisal rights in the merger.

Appraisal rights (also known as dissenters’ rights) are statutory rights that enable stockholders to dissent from certain extraordinary transactions, such as certain mergers, and to demand that the corporation pay the fair value for their shares as determined by a court in a judicial proceeding instead of receiving the consideration offered to stockholders in connection with the applicable transaction. Under Section 910 of the New York Business Corporation Law (the “NYBCL”) and Section 262 of the General Corporation Law of the State of Delaware (“DGCL”), as applicable, Omnicom and IPG stockholders are not entitled to appraisal rights in connection with the issuance of common stock of Omnicom in connection with the merger or the merger. For more information, see the section entitled “No Appraisal Rights” on page 185.

Risks Relating to the Combined Company Following Completion of the Merger

The market price of Omnicom common stock will continue to fluctuate after the merger.

Upon completion of the merger, IPG stockholders who receive merger consideration will become holders of shares of Omnicom common stock, which will trade on the NYSE under the ticker symbol “OMC.” The market price of Omnicom common stock may fluctuate significantly following completion of the merger, and Omnicom stockholders could lose some or all of the value of their investment. In addition, the stock market has experienced significant price and volume fluctuations in recent times, which, if they continue to occur, could adversely affect the market for, or liquidity of, Omnicom common stock, regardless of Omnicom’s actual operating performance.

The market price of Omnicom common stock after the completion of the merger may be affected by factors different from those that historically have affected or currently affect Omnicom common stock.

Upon completion of the merger, IPG stockholders who receive merger consideration will become holders of Omnicom common stock, which will trade on the NYSE under the ticker symbol “OMC.” Omnicom’s business differs from that of IPG, and certain adjustments may be made to the combined company as a result of this transaction. The financial position, results of operations and/or cash flows of the combined company after completion of the merger may be impacted by business conditions affecting IPG that are not currently applicable to Omnicom, and may be different from Omnicom’s financial position, results of operations and/or cash flows before the completion of the merger. Accordingly, the market price of Omnicom common stock after the completion of the merger may be affected by factors different from those currently affecting the market prices of Omnicom common stock. In addition, general fluctuations in stock markets could adversely affect the market for, or liquidity of, Omnicom common stock, regardless of the combined company’s actual operating performance. For a discussion of the businesses of Omnicom and IPG and of some important factors to consider in connection with those businesses, see the section entitled “Information About the Companies” and the documents

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incorporated by reference in the section entitled “Where You Can Find More Information,” including, in particular, the sections entitled “Risk Factors” in each of Omnicom’s and IPG’s Annual Report on Form 10-K for the year ended December 31, 2023 and Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2024, June 30, 2024 and September 30, 2024.

The failure to integrate Omnicom’s and IPG’s businesses and operations successfully in the expected time frame may adversely affect the combined company’s business and results of operations.

Omnicom and IPG have operated and, until the completion of the merger, will continue to operate independently. Following the completion of the merger, Omnicom’s and IPG’s businesses may not be integrated successfully. It is possible that the integration process could result in the loss of Omnicom’s and IPG’s key employees, the loss of clients, service providers, vendors or other business counterparties, the disruption of either company’s or both companies’ ongoing businesses, inconsistencies in standards, controls, procedures and policies, potential unknown liabilities and unforeseen expenses, delays, or regulatory conditions associated with and following completion of the merger; or higher-than-expected integration costs and an overall post-completion integration process that takes longer than originally anticipated. Specifically, the following challenges, among others, must be addressed in integrating Omnicom’s and IPG’s operations in order to realize the anticipated benefits of the merger:

In addition, at times the attention of certain members of either company’s or both companies’ management and resources may be focused on completion of the merger and the integration of the businesses of the two companies and may reduce their availability for day-to-day business operations or other opportunities that may be beneficial, which may disrupt each company’s ongoing operations and the operations of the combined company. Furthermore, following the merger, the board of directors and executive leadership of the combined company will consist of former directors from each of Omnicom and IPG and former executive officers from each of Omnicom and IPG. Combining the boards of directors and management teams of each company into a single board and a single management team could require the reconciliation of differing priorities and philosophies.

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The merger may result in a loss of Omnicom’s and IPG’s clients, service providers, vendors, joint venture participants and other business counterparties, and may result in the termination of existing contracts.

Following the merger, some of Omnicom’s and IPG’s clients, service providers, vendors, joint venture participants and other business counterparties may terminate or scale back their current or prospective business relationships with the combined company. In addition, Omnicom and IPG have contracts with clients, service providers, vendors, joint venture participants and other business counterparties that may require Omnicom or IPG to obtain consents from these other parties in connection with the merger, which may not be obtained on favorable terms or at all. If relationships with clients, service providers, vendors, joint venture participants and other business counterparties are adversely affected by the merger, or if the combined company, following the merger, loses the benefits of the contracts of Omnicom or IPG, the business, financial condition, cash flows and results of operations of the combined company could be adversely affected.

Each of Omnicom and IPG may have material liabilities that are not known to the other party.

Each of Omnicom and IPG may have material liabilities that the other party failed, or was unable, to discover in the course of performing its respective due diligence investigations. Omnicom and IPG may learn additional information about the other party that materially adversely affects it, such as unknown or contingent liabilities and liabilities related to compliance with applicable laws. As a result of these factors, the combined company may incur additional costs and expenses and may be forced to later write-down or write-off assets, restructure operations or incur impairment or other charges that could result in the combined company reporting losses. Even if Omnicom’s and IPG’s respective due diligence has identified certain risks, unexpected risks may arise, and previously known risks may materialize in a manner not consistent with its expectations. If any of these risks materialize, this could adversely affect the combined company’s financial condition and results of operations and could contribute to negative market perceptions about, or price movements of, Omnicom common stock following the merger.

The combined company may fail to realize all of the anticipated benefits of the merger.

The success of the merger will depend, in part, on Omnicom’s ability to realize the cost savings, operating synergies and other benefits from combining Omnicom’s and IPG’s businesses. The anticipated cost savings, operating synergies and other benefits of the merger may not be realized fully or at all, may take longer to realize than expected, or may result in other adverse effects that Omnicom does not currently foresee, in which case, among other things, the merger may not be accretive to adjusted earnings per share for both Omnicom and IPG and may not generate significant cash to return to stockholders via dividends, share repurchases or other means. Some of the assumptions that Omnicom and IPG have made, such as the achievement of the anticipated benefits related to combining complementary assets to create a portfolio of services and products that expand client opportunities, and advances in both companies’ ability to innovate and develop new products and services, may not be realized. The integration process may, for each of Omnicom and IPG, result in the loss of key employees, the disruption of ongoing businesses or inconsistencies in standards, controls, procedures and policies. In addition, there could be potential unknown liabilities and unforeseen expenses associated with the merger that could adversely impact the combined company.

The combined company’s debt may limit its financial flexibility and adversely affect its financial condition, liquidity and results of operations.

As of September 30, 2024, Omnicom’s total outstanding long-term indebtedness was approximately $6.2 billion, including amounts outstanding under its credit facilities and senior notes. As of September 30, 2024, IPG’s total outstanding long-term indebtedness was approximately $2.9 billion, including amounts outstanding under its credit facilities and senior notes. Accordingly, the combined company will have substantial indebtedness following completion of the merger. In addition, subject to the limits contained in the documents governing such indebtedness, the combined company may be able to incur substantial additional debt from time

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to time to finance working capital, capital expenditures, investments or acquisitions or for other purposes. Any increase in the indebtedness of the combined company could have adverse effects on its financial condition, cash flows and results of operations, including by:

In addition, Omnicom and IPG receive credit ratings from rating agencies in the U.S. with respect to their indebtedness. It is anticipated that Omnicom and IPG would seek ratings of the indebtedness of the combined company. Such credit ratings would reflect each rating organization’s opinion of the combined company’s financial strength, operating performance and ability to meet its debt obligations. Such credit ratings would affect the cost and availability of future borrowings and, accordingly, the combined company’s cost of capital. There can be no assurance that the combined company will achieve a particular rating or maintain a particular rating in the future.

The future results of the combined company following the merger will suffer if the combined company does not effectively manage its expanded operations.

Following the merger, the size and complexity of the combined company will increase significantly compared to the business of each of Omnicom and IPG. The combined company’s future success will depend, in part, upon its ability to manage this expanded business, which will pose substantial challenges for management, including challenges related to the management of a larger number of operations and geographies and associated increased costs and complexity. The combined company may also face increased scrutiny from, and/or additional regulatory requirements of, governmental authorities as a result of the significant increase in the size and complexity of its business. There can be no assurances that the combined company will be successful or that it will realize the expected operating synergies, cost savings or other benefits currently anticipated from the merger.

There is no guarantee that Omnicom will continue to declare and pay dividends or repurchase shares of Omnicom common stock following the merger.

Although each of Omnicom and IPG has returned capital to its respective stockholders in the past, through a combination of cash dividends on, and repurchases of, its respective shares of common stock, the board of directors of the combined company may determine not to declare dividends, repurchase shares of its common stock or use other means to return capital to its stockholders in the future or may reduce the amount of capital returned to its stockholders through dividends, share repurchases and other means in the future. Decisions on whether, when, by what means and in what amounts to return capital to its stockholders will remain in the discretion of the board of directors of the combined company (as reconstituted following the merger). Any dividend payment or share repurchase amounts will be determined by the board of directors of the combined company on a quarterly basis, and it is possible that the board of directors of the combined company may increase or decrease the amount of dividends paid or shares repurchased in the future, or determine not to declare

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dividends and/or repurchase shares in the future, at any time and for any reason. Omnicom and IPG expect that any such decisions will depend on the combined company’s financial condition, results of operations, cash balances, cash requirements, future prospects and other considerations that the board of directors of the combined company deems relevant, including,:

Stockholders should be aware that they have no contractual or other legal right to dividends that have not been declared. For additional information, see the section entitled “The Merger—Dividend Policy.”

The combined company may record goodwill and other intangible assets that could become impaired and result in material non-cash charges to the results of operations of the combined company in the future.

In accordance with Accounting Standards Codification Topic 805, Business Combinations (“ASC 805”), the merger will be accounted for as an acquisition by Omnicom pursuant to the acquisition method of accounting for business combinations. Under the acquisition method of accounting, Omnicom will record the net tangible and identifiable intangible assets and liabilities of IPG and its subsidiaries, as of the consummation of the merger, at their respective fair values. The reported financial condition and results of operations of Omnicom for periods after consummation of the merger will reflect IPG balances and results after consummation of the merger but will not be restated retroactively to reflect the historical financial position or results of operations of IPG and its subsidiaries for periods prior to the merger. For additional information, see the section entitled “Unaudited Pro Forma Condensed Combined Financial Statements.”

Under the acquisition method of accounting, the total purchase price will be allocated to IPG’s tangible assets and liabilities and identifiable intangible assets based on their fair values as of the date of completion of the merger, with any excess purchase price allocated to goodwill. To the extent the value of goodwill or intangibles, if any, becomes impaired in the future, the combined company may be required to recognize material non-cash charges relating to such impairment. The combined company’s results of operations may be significantly impacted from both the impairment and the underlying trends in the business that triggered the impairment.

Shares of Omnicom common stock received by IPG stockholders as a result of the merger will have different rights from shares of IPG common stock.

Upon completion of the merger, IPG stockholders will no longer be stockholders of IPG, and IPG stockholders who receive merger consideration will become holders of Omnicom common stock, which will trade on the NYSE under the ticker symbol “OMC.” While IPG is a Delaware corporation and its stockholders’ rights are governed by Delaware law, Omnicom is a New York corporation and the combined company’s stockholder’s rights will be governed by New York law. Given the differences between the DGCL and the NYBCL, as well as Omnicom’s and IPG’s governing documents, there will be important differences between the current rights of IPG stockholders and the rights to which such stockholders will be entitled as Omnicom stockholders. For a discussion of the different rights associated with shares of Omnicom common stock as compared to shares of IPG common stock, see the section entitled “Comparison of Stockholders’ Rights.”

Future sales or issuances of Omnicom common stock could have a negative impact on the Omnicom common stock price.

Based on the number of shares of IPG common stock outstanding as of January 27, 2025 and the number of IPG equity awards currently estimated to be settled in Omnicom common stock following the merger, Omnicom

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expects to issue up to approximately 129,462,731 shares of Omnicom common stock in connection with the merger. The Omnicom common stock that IPG stockholders will receive upon the exchange of IPG common stock for the merger consideration generally may be sold immediately in the public market. It is possible that some former IPG stockholders may seek to sell some or all of the shares of Omnicom common stock they receive as merger consideration, and the merger agreement contains no restriction on the ability of former IPG stockholders to sell such shares of Omnicom common stock following completion of the merger. Other Omnicom stockholders may also seek to sell shares of Omnicom common stock held by them following completion of the merger. These sales or other dispositions of a significant number of shares of Omnicom common stock (or the perception that such sales or other dispositions may occur), coupled with the increase in the outstanding number of shares of Omnicom common stock as a result of the merger (as well as any increase resulting from future issuances of Omnicom common stock), may affect the market for Omnicom common stock in an adverse manner and may cause the price of Omnicom common stock to fall.

Risks Relating to Omnicom’s Business

In addition to the risk factors described above relating to the combined company following completion of the merger, you should read and consider risk factors specific to Omnicom’s businesses that will also affect the combined company after the completion of the merger. These risks are described in Part I, Item 1A of Omnicom’s Annual Report on Form 10-K for the year ended December 31, 2023 and in Part II, Item 1A of Omnicom’s Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2024, June 30, 2024 and September 30, 2024, and in other documents that are incorporated by reference herein. For the location of information incorporated by reference in this joint proxy statement/prospectus, see the section entitled “Where You Can Find More Information.”

Risks Relating to IPG’s Business

In addition to the risk factors described above relating to the combined company following completion of the merger, you should read and consider risk factors specific to IPG’s businesses that will also affect the combined company after the completion of the merger. These risks are described in Part I, Item 1A of IPG’s Annual Report on Form 10-K for the year ended December 31, 2023 and in Part II, Item 1A of IPG’s Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2024, June 30, 2024 and September 30, 2024, and in other documents that are incorporated by reference herein. For the location of information incorporated by reference in this joint proxy statement/prospectus, see the section entitled “Where You Can Find More Information.”

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CAUTIONARY STATEMENT REGARDING FORWARD-LOOKING STATEMENTS

This joint proxy statement/prospectus, and the documents to which Omnicom and IPG refer you in this joint proxy statement/prospectus, as well as oral statements made or to be made by Omnicom and IPG relating to their respective special meetings of stockholders, include certain “forward-looking statements” within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act and the United States Private Securities Litigation Reform Act of 1995, as amended. All statements, other than statements of historical fact, included in this joint proxy statement/prospectus, including those that address activities, events or developments that Omnicom or IPG expects, believes or anticipates will or may occur in the future, are forward-looking statements. Forward-looking statements may be identified by words such as “anticipates,” “believes,” “continue,” “could,” “estimate,” “expects,” “intends,” “will,” “should,” “may,” “plan,” “potential,” “predict,” “project,” “would” or the negative thereof and similar expressions. Such forward-looking statements include, but are not limited to: statements about the benefits of the merger involving Omnicom and IPG, including future financial and operating results, Omnicom’s and IPG’s plans, objectives, expectations and intentions, the expected timing and likelihood of completion of the merger, and other statements that are not historical facts, including the combined company’s ability to create an advanced marketing and sales platform, the combined company’s ability to accelerate innovation and enhance efficiency through the transaction, and the combined company’s plan on future stockholder returns, future results of operations, projected cash flow and liquidity, business strategy and other plans and objectives for future operations. No assurances can be given that the forward-looking statements contained in this joint proxy statement/prospectus will occur as projected and actual results may differ materially from those included in this joint proxy statement/prospectus. Forward-looking statements are based on current expectations, estimates and assumptions that involve a number of risks and uncertainties that could cause actual results to differ materially from those included in this joint proxy statement/prospectus. These risks and uncertainties include, without limitation:

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All of the forward-looking statements Omnicom and IPG make in or in connection with this joint proxy statement/prospectus are qualified by the information contained or incorporated by reference herein, including the information contained under this heading and the information detailed in Omnicom’s Annual Report on Form 10-K for the year ended December 31, 2023 and Omnicom’s Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and other filings Omnicom makes with the SEC, which are incorporated herein by reference, and in IPG’s Annual Report on Form 10-K for the year ended December 31, 2023 and IPG’s Quarterly Reports on Form 10-Q, Current Reports on Form 8-K and other filings IPG makes with the SEC, which are incorporated herein by reference. For additional information, see the sections entitled “Risk Factors” and “Where You Can Find More Information” beginning on pages 32 and 197, respectively.

Forward-looking statements are based on the estimates and opinions of management at the time the statements are made. Except to the extent required by applicable law, neither Omnicom nor IPG undertakes any obligation to publicly update or revise any forward-looking statement, whether as a result of new information, future events or otherwise. You are cautioned not to place undue reliance on these forward-looking statements that speak only as of the date hereof.

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INFORMATION ABOUT THE COMPANIES

Omnicom Group Inc.

280 Park Avenue

New York, New York 10017

Telephone: (212) 415-3600

Omnicom is a leading provider of data-inspired, creative marketing and sales solutions. Omnicom’s iconic agency brands are home to the industry’s most innovative communications specialists who are focused on driving intelligent business outcomes for their clients. The company offers a wide range of services in strategic media planning and buying, precision marketing, retail and digital commerce, advertising, branding, experiential, public relations, healthcare marketing and other specialty marketing services to over 5,000 clients in more than 70 countries. Omnicom common stock is listed on the NYSE, trading under the symbol “OMC.”

For additional information about Omnicom and its subsidiaries, see the documents incorporated by reference in this joint proxy statement/prospectus in the section entitled “Where You Can Find More Information” beginning on page 197.

The Interpublic Group of Companies, Inc.

909 Third Avenue

New York, New York 10022

Telephone: (212) 704-1200

IPG is a values-based, data-fueled, and creatively-driven provider of marketing solutions. Home to some of the world’s best-known and most innovative communications specialists, IPG global brands include Acxiom, Craft, FCB, FutureBrand, Golin, Initiative, IPG Health, IPG Mediabrands, Jack Morton, KINESSO, MAGNA, McCann, Mediahub, Momentum, MRM, MullenLowe, Octagon, UM, Weber Shandwick and more. IPG common stock is listed on the NYSE, trading under the symbol “IPG.”

For additional information about IPG and its subsidiaries, see the documents incorporated by reference in this joint proxy statement/prospectus in the section entitled “Where You Can Find More Information” beginning on page 197.

EXT Subsidiary Inc.

c/o Omnicom Group Inc.

280 Park Avenue

New York, New York 10017

Phone: (212) 415-3600

Merger Sub is a direct wholly owned subsidiary of Omnicom. Upon the completion of the merger, Merger Sub will cease to exist. Merger Sub was incorporated in Delaware on December  6, 2024 for the sole purpose of effecting the merger.

The Combined Company

Upon the completion of the merger, IPG will be a direct wholly owned subsidiary of Omnicom and its shares of common stock will cease trading on the NYSE. The combined company will retain Omnicom’s current headquarters in New York, New York. Omnicom and IPG have also agreed to certain governance matters relating to the board of directors and management of the combined company following the completion of the merger. See “The Merger—Board of Directors and Management of Omnicom Following the Completion of the Merger” and “The Merger Agreement—Organizational Documents; Directors and Officers” for more information.

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SPECIAL MEETING OF OMNICOM STOCKHOLDERS

Date, Time and Place

The Omnicom special meeting will be held virtually via live webcast on March 18, 2025, at 9:00 a.m. Eastern Time. Because the Omnicom special meeting is completely virtual and being conducted via live webcast, Omnicom stockholders will not be able to attend the Omnicom special meeting in person. Omnicom stockholders will be able to attend the Omnicom special meeting online and vote their shares and submit questions electronically during the meeting by visiting www.virtualshareholdermeeting.com/OMC2025SM. Omnicom stockholders will need the 16-digit control number found on their proxy cards in order to access the Omnicom special meeting website.

Purpose of the Omnicom Special Meeting

The purpose of the Omnicom special meeting is to consider and vote on the following proposals:

Omnicom will transact no other business at the Omnicom special meeting or any adjournment thereof, except such business as may properly be brought before the Omnicom special meeting by or at the direction of the Omnicom board in accordance with the Omnicom bylaws.

Recommendation of the Omnicom Board of Directors

The Omnicom board unanimously recommends that Omnicom stockholders vote “FOR” the Omnicom issuance proposal and “FOR” the Omnicom adjournment proposal.

For additional information on the recommendation of the Omnicom board, see the section entitled “The Merger—Recommendation of the Omnicom Board of Directors and Reasons for the Merger.”

Record Date and Outstanding Shares of Omnicom Common Stock

Only holders of record of issued and outstanding shares of Omnicom common stock as of the close of business on January 27, 2025, the record date for the Omnicom special meeting, are entitled to receive notice of, and to vote at, the Omnicom special meeting, whether via the Omnicom special meeting website or by proxy, or any adjournment or postponement thereof.

As of the close of business on the record date, there were 196,480,662 shares of Omnicom common stock issued and outstanding and entitled to vote at the Omnicom special meeting. Omnicom stockholders may cast one vote for each share of Omnicom common stock held by them as of the close of business on the record date.

A complete list of Omnicom stockholders entitled to vote at the Omnicom special meeting will be available for inspection at Omnicom’s offices in New York, New York during ordinary business hours for a period of no less than ten days before the Omnicom special meeting. If you would like to examine the list of Omnicom stockholders, please contact the Omnicom Secretary at 280 Park Avenue, New York, New York 10017.

Quorum; Abstentions, Broker Non-Votes and Failure to Vote

A quorum of Omnicom stockholders is necessary for Omnicom to conduct business at the Omnicom special meeting. The presence, via the Omnicom special meeting website or by proxy, of the holders of a majority of the outstanding shares of Omnicom common stock entitled to vote at the Omnicom special meeting will constitute a quorum for the transaction of business. Abstentions will be counted for purposes of determining whether a

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quorum exists; however, broker non-votes will not be counted for purposes of determining whether a quorum exists. If you submit a properly executed proxy card, even if you vote “against” the Omnicom proposals or “abstain” from voting on the Omnicom proposals, your shares of Omnicom common stock will be counted for purposes of calculating whether a quorum is present.

If you are a stockholder of record and you do not provide your proxy by signing and returning your proxy card or via the Internet, by telephone or vote at the Omnicom special meeting via the Omnicom special meeting website, your shares will not be voted at the Omnicom special meeting and will not be counted as present for purposes of determining whether a quorum exists.

Under the current NYSE rules, brokers, banks or other nominees do not have discretionary authority to vote on any of the Omnicom proposals at the Omnicom special meeting. Because all of the proposals for consideration at the Omnicom special meeting are “non-routine,” it is not expected that there will be any broker non-votes at the Omnicom special meeting. However, if there are any broker non-votes, they will have no effect on the outcome of the Omnicom issuance proposal or the Omnicom adjournment proposal.

Executed but unvoted proxies will be voted in accordance with the recommendation of the Omnicom board.

Required Vote

The votes required for each Omnicom proposal are as follows:

An abstention occurs when the beneficial owner of shares, or a broker, bank or other nominee holding shares for a beneficial owner, is present via the Omnicom special meeting website or by proxy at the Omnicom special meeting and entitled to vote at the meeting, but such person refrains from voting as to a particular proposal by expressly marking the “abstain” box on the voting instruction form or ballot.

A broker non-vote occurs when a broker, bank or other nominee returns a valid proxy card without voting on such proposal because they did not receive voting instructions from the street name holder and do not have discretionary authority to vote the shares on a particular proposal. Shares represented by broker non-votes will not be voted on any proposal for which the broker, bank or other nominee has no discretionary authority to vote.

Under applicable rules, brokers or other nominees have discretionary voting power with respect to matters that are considered routine. Brokers will not be permitted to vote shares of Omnicom common stock at the Omnicom special meeting with respect to any of the Omnicom proposals at the Omnicom special meeting without receiving instructions from the beneficial owner of such shares.

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The Omnicom issuance proposal and the Omnicom adjournment proposal are described in the section entitled “Omnicom Proposals.”

Methods of Voting

Omnicom stockholders of record may vote by providing their proxies via the Internet by going to the web address provided on the enclosed proxy card and following the instructions for Internet voting, by phone using the toll-free phone number listed on the enclosed proxy card, or by completing, signing, dating and returning the enclosed proxy card in the postage-paid envelope provided.

Omnicom stockholders of record may vote their shares via the Omnicom special meeting website at the Omnicom special meeting or by submitting their proxies:

Omnicom stockholders who hold their shares in “street name” by a broker, bank or other nominee should refer to the voting instruction form or other information forwarded by their broker, bank or other nominee for instructions on how to vote their shares.

Omnicom stockholders who hold shares as participants in Omnicom’s employee retirement savings plan or employee stock purchase plan must provide their voting instructions to the trustee of the employee retirement savings plan or administrator of the employee stock purchase plan, as applicable, by 11:59 p.m. Eastern Time on March 13, 2025. If timely voting instructions are not provided, the trustee of Omnicom’s employee retirement savings plan will vote uninstructed shares in the same proportion on each proposal as it votes all other shares for which it has received timely voting instructions, while the administrator of Omnicom’s employee stock purchase plan will not vote uninstructed shares.  

Voting via the Omnicom Special Meeting Website

Shares held directly in your name as stockholder of record may be voted at the Omnicom special meeting via the Omnicom special meeting website. If you choose to attend the Omnicom special meeting and vote your shares via the Omnicom special meeting website, you will need the 16-digit control number included on your proxy card. Even if you plan to attend the Omnicom special meeting, the Omnicom board recommends that you vote your shares in advance so that your vote will be counted if you later decide not to attend the Omnicom special meeting.

If you are a beneficial holder and your broker, bank or other nominee has not provided you with a 16-digit control number on the voting instruction form it furnishes you, you will need to obtain a control number from your broker, bank or other nominee holder of record giving you the right to vote the shares at the Omnicom special meeting.

Questions About Voting

If you have any questions about how to vote or direct a vote in respect of your shares of Omnicom common stock, you may contact Innisfree, Omnicom’s proxy solicitor, toll-free at (877) 717-3898, or for banks and brokers, collect at (212) 750-5833.

Adjournment

If the Omnicom special meeting is adjourned, Omnicom stockholders who have already submitted their proxies will be able to revoke them at any time prior to their use. At any subsequent reconvening of the

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Omnicom special meeting, all proxies will be voted in the same manner as the manner in which such proxies would have been voted at the original Omnicom special meeting, except for any proxies that have been validly revoked or withdrawn prior to the subsequent meeting.

The merger agreement provides that Omnicom may adjourn, postpone or otherwise delay the Omnicom special meeting:

However, unless otherwise agreed to by IPG and Omnicom, the Omnicom special meeting will not be adjourned or postponed for more than ten business days in the aggregate from the originally scheduled meeting date of March 18, 2025.

Revocability of Proxies

If you are a stockholder of record of Omnicom, whether you vote by phone, the Internet or mail, you can change or revoke your proxy before it is voted at the meeting in one of the following ways:

If you are a beneficial owner of Omnicom common stock as of the close of business on the record date, you must follow the instructions of your broker, bank or other nominee to revoke your voting instructions.

Proxy Solicitation Costs

The enclosed proxy card is being solicited by Omnicom and the Omnicom board. In addition to solicitation by mail, Omnicom’s directors, officers and employees may solicit proxies in person, by phone or by electronic means. These persons will not be specifically compensated for conducting such solicitation.

Omnicom has retained Innisfree to assist in the solicitation process. Omnicom will pay Innisfree a fee of up to $112,500, as well as reasonable and customary documented expenses.

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Omnicom also has agreed to indemnify Innisfree against various liabilities and expenses that relate to or arise out of its solicitation of proxies (subject to certain exceptions).

Omnicom will ask brokers, banks and other nominees to forward the proxy solicitation materials to the beneficial owners of shares of Omnicom common stock held of record by such nominee holders. Omnicom will reimburse these nominee holders for their customary clerical and mailing expenses incurred in forwarding the proxy solicitation materials to the beneficial owners.

No Appraisal Rights

Under New York law, Omnicom stockholders are not entitled to appraisal rights in connection with the issuance of shares of Omnicom common stock as contemplated by the merger agreement.

For more information, see the section entitled “No Appraisal Rights” on page 185.

Other Information

The matters to be considered at the Omnicom special meeting are of great importance to the Omnicom stockholders. Accordingly, you are urged to read and carefully consider the information contained in or incorporated by reference into this joint proxy statement/prospectus and submit your proxy by phone or the Internet or complete, date, sign and promptly return the enclosed proxy card in the enclosed postage-paid envelope. If you submit your proxy by phone or the Internet, you do not need to return the enclosed proxy card.

Assistance

If you need assistance in completing your proxy card or have questions regarding the Omnicom special meeting, contact:

Innisfree M&A Incorporated

501 Madison Avenue, 20th Floor

New York, New York 10022

Stockholders Call (Toll-Free): (877) 717-3898

Banks and Brokers Call: (212) 750-5833

Vote of Omnicom’s Directors and Executive Officers

As of January 27, 2025, the record date for the Omnicom special meeting, Omnicom directors and executive officers, and their affiliates, as a group, owned and were entitled to vote 1,696,476 shares of Omnicom common stock, or approximately 0.9% of the total outstanding shares of Omnicom common stock as of such date.

Omnicom currently expects that all of its directors and executive officers will vote their shares “FOR” the Omnicom issuance proposal and “FOR” the Omnicom adjournment proposal.

Attending the Omnicom Special Meeting Virtually

You are entitled to attend the Omnicom special meeting only if you are a stockholder of record of Omnicom at the close of business on the record date or you held your shares of Omnicom common stock beneficially in the name of a broker, bank or other nominee as of the record date, or if you hold a valid proxy for the Omnicom special meeting.

If you were a stockholder of record of Omnicom at the close of business on the record date and wish to attend the Omnicom special meeting, you will need the 16-digit control number located on your proxy card.

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If a broker, bank or other nominee is the record owner of your shares of Omnicom common stock and your broker, bank or other nominee has not provided you with a 16-digit control number on the voting instruction form it furnishes you, you will need to obtain your control number and further instructions from your broker, bank or other nominee to attend the Omnicom special meeting.

Results of the Omnicom Special Meeting

Within four business days following the Omnicom special meeting, Omnicom intends to file the final voting results with the SEC on a Current Report on Form 8-K. If the final voting results have not been certified within that four business-day-period, Omnicom will report the preliminary voting results on a Current Report on Form 8-K at that time and will file an amendment to the Current Report on Form 8-K to report the final voting results within four business days of the date that the final results are certified.

OMNICOM STOCKHOLDERS SHOULD CAREFULLY READ THIS JOINT PROXY STATEMENT/ PROSPECTUS IN ITS ENTIRETY FOR MORE DETAILED INFORMATION CONCERNING THE OMNICOM PROPOSALS.

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OMNICOM PROPOSALS

Omnicom Issuance Proposal

It is a condition to the completion of the merger that Omnicom stockholders approve the issuance of shares of Omnicom common stock in the merger. In the merger, each IPG stockholder will receive, for each eligible share of IPG common stock that is issued and outstanding as of immediately prior to the effective time of the merger, the merger consideration of 0.344 shares of Omnicom common stock, with cash paid in lieu of fractional shares, as further described in the sections entitled “The Merger—Consideration to IPG Stockholders” and “The Merger Agreement—Effect of the Merger on Capital Stock; Merger Consideration.”

Under NYSE rules, a company is required to obtain stockholder approval prior to the issuance of shares of common stock if the number of shares of common stock to be issued is, or will be upon issuance, equal to or in excess of 20% of the number of shares of common stock outstanding before the issuance of the shares of common stock. If the merger is completed pursuant to the merger agreement, Omnicom expects to issue approximately 129,462,731 shares of Omnicom common stock in connection with the merger based on the number of shares of IPG common stock outstanding as of January 27, 2025 and the number of IPG equity awards currently estimated to be settled in Omnicom common stock in connection with the merger. Accordingly, the aggregate number of shares of Omnicom common stock that Omnicom will issue in the merger will exceed 20% of the shares of Omnicom common stock outstanding before such issuance, and for this reason, Omnicom is seeking the approval of Omnicom stockholders for the issuance of shares of Omnicom common stock pursuant to the merger agreement. In the event the Omnicom issuance proposal is not approved by Omnicom stockholders, the merger will not be completed.

In the event the Omnicom issuance proposal is approved by Omnicom stockholders, but the merger agreement is terminated (without the merger being completed) prior to the issuance of shares of Omnicom common stock pursuant to the merger agreement, Omnicom will not issue any shares of Omnicom common stock as a result of the approval of the Omnicom issuance proposal.

Approval of the Omnicom issuance proposal requires the affirmative vote of the holders of a majority of the shares voting on the proposal. Abstentions, broker non-votes or any failure by an Omnicom stockholder to vote (e.g., by not submitting a proxy and not voting at the Omnicom special meeting) will have no effect on the outcome of the Omnicom issuance proposal.

The Omnicom board unanimously recommends that you vote “FOR” the Omnicom issuance proposal.

Omnicom Adjournment Proposal

Omnicom stockholders are being asked to approve a proposal that will grant the Omnicom board authority to adjourn the Omnicom special meeting, if necessary or appropriate, to permit the further solicitation of additional votes or proxies if there are not sufficient votes to approve the Omnicom issuance proposal. Approval of this proposal is not a condition to the completion of the merger.

If the Omnicom adjournment proposal is approved, the Omnicom special meeting could be adjourned to any date. If the Omnicom special meeting is adjourned, Omnicom stockholders who have already submitted their proxies will be able to revoke them at any time prior to their use. If it is necessary to adjourn the Omnicom special meeting, no notice of the adjourned Omnicom special meeting is required to be given to Omnicom stockholders so long as (i) the place, the date and time of, as well as the means of electronic communications by which stockholders may participate in and/or vote at, the adjourned Omnicom special meeting is announced at the Omnicom special meeting and (ii) Omnicom does not fix a new record date for the adjourned meeting.

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When a quorum is present, approval of the Omnicom adjournment proposal requires the affirmative vote of the holders of a majority of the shares voting on the proposal. Abstentions, broker non-votes or any failure by an Omnicom stockholder to vote (e.g., by not submitting a proxy and not voting at the Omnicom special meeting) will have no effect on the outcome of the Omnicom adjournment proposal when a quorum is present.

When a quorum is not present, approval of the Omnicom adjournment proposal requires the affirmative vote of the holders of a majority of the shares entitled to vote at the meeting who are present or represented by proxy. Abstentions will have the same effect as a vote “AGAINST” the adjournment proposal, while broker non-votes or any failure by an Omnicom stockholder to vote (e.g., by not submitting a proxy and not voting at the Omnicom special meeting) will have no effect on the outcome of the Omnicom adjournment proposal when a quorum is not present.

The Omnicom board unanimously recommends that you vote “FOR” the Omnicom adjournment proposal.

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SPECIAL MEETING OF IPG STOCKHOLDERS

Date, Time and Place

The IPG special meeting will be held virtually via live webcast on March 18, 2025, at 9:00 a.m. Eastern Time. Because the IPG special meeting is completely virtual and being conducted via live webcast, IPG stockholders will not be able to attend the IPG special meeting in person. IPG stockholders will be able to attend the IPG special meeting online and vote their shares and submit questions electronically during the meeting by visiting www.virtualshareholdermeeting.com/IPG2025SM. IPG stockholders will need the 16-digit control number found on their proxy cards in order to access the IPG special meeting website.

Purpose of the IPG Special Meeting

The purpose of the IPG special meeting is to consider and vote on the following proposals:

IPG will transact no other business at the IPG special meeting or any adjournment thereof, except such business as may properly be brought before the IPG special meeting by or at the direction of the IPG board in accordance with the IPG bylaws.

Recommendation of the IPG Board of Directors

The IPG board unanimously recommends that IPG stockholders vote “FOR” the IPG merger proposal, “FOR” the IPG compensation proposal and “FOR” the IPG adjournment proposal.

For additional information on the recommendation of the IPG board, see the section entitled “The Merger—Recommendation of the IPG Board of Directors and Reasons for the Merger.”

Record Date and Outstanding Shares of IPG Common Stock

Only holders of record of issued and outstanding shares of IPG common stock as of the close of business on January 27, 2025, the record date for the IPG special meeting, are entitled to receive notice of, and to vote at, the IPG special meeting, whether via the IPG special meeting website or by proxy, or any adjournment or postponement thereof.

As of the close of business on the record date, there were 372,645,940 shares of IPG common stock issued and outstanding. IPG stockholders may cast one vote for each share of IPG common stock held by them as of the close of business on the record date.

A complete list of IPG stockholders entitled to vote at the IPG special meeting will be available for inspection at IPG’s offices in New York, New York during ordinary business hours for a period of no less than ten days before the IPG special meeting. If you would like to examine the list of IPG stockholders, please contact the IPG SVP  & Secretary at 909 Third Avenue, New York, NY 10022.

Quorum; Abstentions, Broker Non-Votes and Failure to Vote

A quorum of IPG stockholders is necessary for IPG to conduct business at the IPG special meeting. The presence, via the IPG special meeting website or by proxy, of the holders of a majority of the outstanding shares of IPG common stock entitled to vote at the IPG special meeting will constitute a quorum for the transaction of

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business. If you submit a properly executed proxy card, even if you vote “against” the IPG proposals or “abstain” from voting on the IPG proposals, your shares of IPG common stock will be counted for purposes of calculating whether a quorum is present.

If you are a stockholder of record and you do not provide your proxy by signing and returning your proxy card or via the Internet, by telephone or vote at the IPG special meeting via the IPG special meeting website, your shares will not be voted at the IPG special meeting and will not be counted as present for purposes of determining whether a quorum exists.

Because all of the proposals for consideration at the IPG special meeting are “non-routine” under applicable NYSE rules, brokers, banks and other nominees do not have discretionary authority to vote on any of the IPG proposals and will not be able to vote on any of the IPG proposals absent instructions from the beneficial owner. Accordingly, it is not expected that there will be any broker non-votes at the IPG special meeting. Broker non-votes, if any, will not be considered present and entitled to vote on any of the IPG proposals for the purpose of determining the presence of a quorum with respect to the vote thereon.

Executed but unvoted proxies will be voted in accordance with the recommendation of the IPG board.

Required Vote

The votes required for each IPG proposal are as follows:

An abstention occurs when the beneficial owner of shares, or a broker, bank or other nominee holding shares for a beneficial owner, is present via the IPG special meeting website or by proxy at the IPG special meeting, and entitled to vote at the meeting, but such person refrains from voting as to a particular proposal by expressly marking the “abstain” box on the voting instruction form or ballot.

A broker non-vote occurs when a broker, bank or other nominee returns a valid proxy card without voting on such proposal because they did not receive voting instructions from the street name holder and do not have

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discretionary authority to vote the shares on a particular proposal. Shares represented by broker non-votes will not be voted on any proposal for which the broker, bank or other nominee has no discretionary authority to vote.

Under applicable rules, brokers or other nominees have discretionary voting power with respect to matters that are considered routine. Brokers will not be permitted to vote shares of IPG common stock at the IPG special meeting with respect to any of the IPG proposals at the IPG special meeting without receiving instructions from the beneficial owner of such shares.

The IPG merger proposal, the IPG compensation proposal and the IPG adjournment proposal are described in the section entitled “IPG Proposals.”

Methods of Voting

IPG stockholders of record may vote by providing their proxies via the Internet by going to the web address provided on the enclosed proxy card and following the instructions for Internet voting, by phone using the toll-free phone number listed on the enclosed proxy card, or by completing, signing, dating and returning the enclosed proxy card in the postage-paid envelope provided.

IPG stockholders of record may vote their shares via the IPG special meeting website at the IPG special meeting or by submitting their proxies:

IPG stockholders who hold their shares in “street name” by a broker, bank or other nominee should refer to the voting instruction form or other information forwarded by their broker, bank or other nominee for instructions on how to vote their shares.

Participants in the IPG savings plan may vote the number of shares of IPG common stock equivalent to the interest in IPG common stock credited to their accounts under the IPG savings plan as of the record date. Participants may vote by instructions given to Empower Trust Company, LLC, the trustee of the IPG savings plan (the “Trustee”), pursuant to the enclosed proxy card. The Trustee will vote shares in accordance with duly executed instructions if received on or before March 14, 2025. If the Trustee does not receive timely instructions, the shares of IPG common stock equivalent to the interest in IPG common stock credited to that participant’s account, will not be voted by the Trustee. The Trustee will vote any shares of IPG common stock held by the IPG savings plan that are not specifically allocated to any individual savings plan participant in the same proportion that the Trustee votes the IPG common stock for which it receives timely instructions from IPG savings plan participants.

Voting via the IPG Special Meeting Website

Shares held directly in your name as stockholder of record may be voted at the IPG special meeting via the IPG special meeting website. If you choose to attend the IPG special meeting and vote your shares via the IPG special meeting website, you will need the 16-digit control number included on your proxy card. Even if you plan to attend the IPG special meeting, the IPG board recommends that you vote your shares in advance so that your vote will be counted if you later decide not to attend the IPG special meeting.

If you are a beneficial holder and your broker, bank or other nominee has not provided you with a 16-digit control number on the voting instruction form it furnishes you, you will need to obtain a control number from your broker, bank or other nominee holder of record giving you the right to vote the shares at the IPG special meeting.

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Questions About Voting

If you have any questions about how to vote or direct a vote in respect of your shares of IPG common stock, you may contact D.F. King, IPG’s proxy solicitor, at (800) 669-5550 (toll free), (212) 434-0035 (collect call), or at IPG@dfking.com.

Adjournment

If the IPG special meeting is adjourned, IPG stockholders who have already submitted their proxies will be able to revoke them at any time prior to their use. At any subsequent reconvening of the IPG special meeting, all proxies will be voted in the same manner as the manner in which such proxies would have been voted at the original IPG special meeting, except for any proxies that have been validly revoked or withdrawn prior to the subsequent meeting.

The merger agreement provides that IPG may adjourn, postpone or otherwise delay the IPG special meeting:

However, unless otherwise agreed to by Omnicom and IPG, the IPG special meeting will not be adjourned or postponed for more than ten business days in the aggregate from the originally scheduled meeting date of March 18, 2025.

Revocability of Proxies

If you are a stockholder of record of IPG, whether you vote by phone, the Internet or mail, you can change or revoke your proxy before it is voted at the meeting in one of the following ways:

If you are a beneficial owner of IPG common stock as of the close of business on the record date, you must follow the instructions of your broker, bank or other nominee to revoke your voting instructions.

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Proxy Solicitation Costs

The enclosed proxy card is being solicited by IPG and the IPG board. In addition to solicitation by mail, IPG’s directors, officers and employees may solicit proxies in person, by phone or by electronic means. These persons will not be specifically compensated for conducting such solicitation.

IPG has retained D.F. King to assist in the solicitation process. IPG will pay D.F. King a fee of approximately $100,000, as well as reasonable and customary documented expenses. IPG also has agreed to indemnify D.F. King against various liabilities and expenses that relate to or arise out of its solicitation of proxies (subject to certain exceptions).

IPG will ask brokers, banks and other nominees to forward the proxy solicitation materials to the beneficial owners of shares of IPG common stock held of record by such nominee holders. IPG will reimburse these nominee holders for their customary clerical and mailing expenses incurred in forwarding the proxy solicitation materials to the beneficial owners.

No Appraisal Rights

Under Delaware law, IPG stockholders are not entitled to appraisal rights in connection with the issuance of shares of Omnicom common stock as contemplated by the merger agreement.

For more information, see the section entitled “No Appraisal Rights” on page 185.

Other Information

The matters to be considered at the IPG special meeting are of great importance to the IPG stockholders. Accordingly, you are urged to read and carefully consider the information contained in or incorporated by reference into this joint proxy statement/prospectus and submit your proxy by phone or the Internet or complete, date, sign and promptly return the enclosed proxy card in the enclosed postage-paid envelope. If you submit your proxy by phone or the Internet, you do not need to return the enclosed proxy card.

Assistance

If you need assistance in completing your proxy card or have questions regarding the IPG special meeting, contact:

D.F. King & Co., Inc.

48 Wall Street, 22nd Floor New York, NY 10005

Banks and Brokers Call Collect: (212) 434-0035

All Others Call Toll-Free: (800) 669-5550

Email: IPG@dfking.com

Vote of IPG’s Directors and Executive Officers

As of January 27, 2025, the record date for the IPG special meeting, IPG directors and executive officers, and their affiliates, as a group, owned and were entitled to vote 900,045 shares of IPG common stock, or approximately 0.2% of the total outstanding shares of IPG common stock as of such date.

IPG currently expects that all of its directors and executive officers will vote their shares “FOR” the IPG merger proposal, “FOR” the IPG compensation proposal and “FOR” the IPG adjournment proposal.

Attending the IPG Special Meeting Virtually

You are entitled to attend the IPG special meeting only if you are a stockholder of record of IPG at the close of business on the record date or you held your shares of IPG common stock beneficially in the name of a broker, bank or other nominee as of the record date, or if you hold a valid proxy for the IPG special meeting.

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If you were a stockholder of record of IPG at the close of business on the record date and wish to attend the IPG special meeting, you will need the 16-digit control number located on your proxy card.

If a broker, bank or other nominee is the record owner of your shares of IPG common stock and your broker, bank or other nominee has not provided you with a 16-digit control number on the voting instruction form it furnishes you, you will need to obtain your control number and further instructions from your broker, bank or other nominee to attend the IPG special meeting.

Results of the IPG Special Meeting

Within four business days following the IPG special meeting, IPG intends to file the final voting results with the SEC on a Current Report on Form 8-K. If the final voting results have not been certified within that four-business-day period, IPG will report the preliminary voting results on a Current Report on Form 8-K at that time and will file an amendment to the Current Report on Form 8-K to report the final voting results within four business days of the date that the final results are certified.

IPG STOCKHOLDERS SHOULD CAREFULLY READ THIS JOINT PROXY STATEMENT/PROSPECTUS IN ITS ENTIRETY FOR MORE DETAILED INFORMATION CONCERNING THE IPG PROPOSALS.

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IPG PROPOSALS

IPG Merger Proposal

It is a condition to the completion of the merger that IPG stockholders approve the IPG merger proposal. In the merger, each IPG stockholder will receive, for each eligible share of IPG common stock that is issued and outstanding as of immediately prior to the effective time of the merger, the merger consideration of 0.344 shares of Omnicom common stock, with cash paid in lieu of fractional shares, as further described in the sections entitled “The Merger—Consideration to IPG Stockholders” and “The Merger Agreement—Effect of the Merger on Capital Stock; Merger Consideration.”

Pursuant to Section 251 of the DGCL and in order to fulfill a condition to the consummation of the merger contained in the merger agreement, IPG stockholders are being asked to adopt the merger agreement as it relates to the merger.

The IPG board has unanimously determined that the terms of the merger agreement and the transactions contemplated by the merger agreement, including the merger, are advisable, fair to, and in the best interests of, IPG and its stockholders; has unanimously approved, authorized and adopted the merger agreement and the transactions contemplated by the merger agreement, including the merger. For a summary of the merger agreement and the merger, including the background of the merger, IPG’s reasons for the merger, the opinion of IPG’s financial advisor and related matters, see the sections entitled “The Merger” beginning on page 65 and “The Merger Agreement” beginning on page 128.

Approval of the IPG merger proposal requires the affirmative vote of a majority of the outstanding shares of IPG common stock entitled to vote on such proposal. Abstentions, broker non-votes, or any failure by an IPG stockholder to vote (e.g., by not submitting a proxy and not voting at the IPG special meeting) will have the same effect as a vote “AGAINST” the IPG merger proposal.

The IPG board unanimously recommends that you vote “FOR” the IPG merger proposal.

IPG Compensation Proposal

As required by Section 14A of the Exchange Act and the applicable SEC rules issued thereunder, which were enacted pursuant to the Dodd-Frank Wall Street Reform and Consumer Protection Act, IPG is required to provide its stockholders the opportunity to vote to approve, by a non-binding advisory vote, certain compensation that may be paid or become payable to IPG’s named executive officers that is based on or otherwise relates to the merger, as described in the section entitled “The Merger—Interests of IPG Directors and Executive Officers in the Merger—Quantification of Potential Payments and Benefits to IPG’s Named Executive Officers—Golden Parachute Compensation.” Accordingly, IPG stockholders are being provided the opportunity to cast an advisory vote on such payments. As an advisory vote, this proposal is not binding upon IPG or the IPG board, or upon Omnicom or the Omnicom board, and approval of this proposal is not a condition to the completion of the merger and is a vote separate and apart from the IPG merger proposal and the IPG adjournment proposal. Accordingly, you may vote to approve the IPG merger proposal and the IPG adjournment proposal and vote not to approve the IPG compensation proposal and vice-versa. Because the merger-related executive compensation to be paid in connection with the merger is based on the terms of the merger agreement as well as the contractual arrangements with IPG’s named executive officers, such compensation will be payable, regardless of the outcome of this advisory vote, if the merger is completed (subject only to the contractual conditions applicable thereto). However, IPG seeks the support of its stockholders and believes that stockholder support is appropriate as the executive compensation programs are designed to incentivize executives to successfully execute a transaction such as that contemplated by the merger from its early stages until consummation. Accordingly, IPG stockholders are being asked to vote on the following resolution:

RESOLVED, that the stockholders of The Interpublic Group of Companies, Inc. approve, on an advisory, non-binding basis, certain compensation that may be paid or become payable to the named executive officers of

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The Interpublic Group of Companies, Inc. that is based on or otherwise relates to the merger, as disclosed pursuant to Item 402(t) of Regulation S-K under the heading “The Merger—Interests of IPG Directors and Executive Officers in the Merger—Quantification of Potential Payments and Benefits to IPG’s Named Executive Officers—Golden Parachute Compensation.”

Approval of the IPG compensation proposal, which is a non-binding advisory proposal, requires the affirmative vote of a majority of the shares of IPG common stock present via the IPG special meeting website or by proxy at the IPG special meeting and entitled to vote on such proposal. Abstentions will have the same effect as a vote “AGAINST” the proposal. Broker non-votes, or any failure by an IPG stockholder to vote (e.g., by not submitting a proxy and not voting at the IPG special meeting) will have no effect on the outcome of the IPG compensation proposal. As an advisory vote, this proposal is not binding on IPG or the IPG board or Omnicom or the Omnicom board, and approval of this proposal is not a condition to the completion of the merger.

The IPG board unanimously recommends that you vote “FOR” the IPG compensation proposal.

IPG Adjournment Proposal

IPG stockholders are being asked to approve a proposal that will grant the IPG board authority to adjourn the IPG special meeting, if necessary or appropriate, to permit the further solicitation of additional votes or proxies if there are not sufficient votes to approve the IPG merger proposal. Approval of this proposal is not a condition to the completion of the merger.

If the IPG adjournment proposal is approved, the IPG special meeting could be adjourned to any date. If the IPG special meeting is adjourned, IPG stockholders who have already submitted their proxies will be able to revoke them at any time prior to their use. If it is necessary to adjourn the IPG special meeting, no notice of the adjourned IPG special meeting is required to be given to IPG stockholders so long as (i) the time and place of the adjourned IPG special meeting is announced at the IPG special meeting, (ii) the adjourned IPG special meeting occurs within 30 days of the original date for the IPG special meeting, and (iii) IPG does not, after the adjournment, fix a new record date for the adjourned IPG special meeting.

Approval of the IPG adjournment proposal requires the affirmative vote of a majority of the shares of IPG common stock present via the IPG special meeting website or by proxy at the IPG special meeting and entitled to vote on such proposal, whether or not a quorum is present. Abstentions will have the same effect as a vote “AGAINST” the proposal. Broker non-votes, or any failure by an IPG stockholder to vote (e.g., by not submitting a proxy and not voting at the IPG special meeting) will have no effect on the outcome of the IPG adjournment proposal.

The IPG board unanimously recommends that you vote “FOR” the IPG adjournment proposal.

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THE MERGER

This discussion of the merger is qualified in its entirety by reference to the merger agreement, which is attached to this joint proxy statement/prospectus as Annex A and incorporated by reference herein in its entirety. You should read the entire merger agreement carefully as it is the legal document that governs the merger.

Transaction Structure

At the effective time of the merger, Merger Sub will merge with and into IPG. As a result of the merger, the separate corporate existence of Merger Sub will cease, and IPG will continue as the surviving corporation in the merger and as a direct wholly owned subsidiary of Omnicom.

Consideration to IPG Stockholders

As a result of the merger, each eligible share of IPG common stock issued and outstanding immediately prior to the effective time of the merger will be converted into the right to receive 0.344 shares of Omnicom common stock.

IPG stockholders will not be entitled to receive any fractional shares of Omnicom common stock, nor any dividends, voting rights or any other rights in respect of the fractional shares, in the merger. IPG stockholders that would have otherwise been entitled to receive a fractional share of Omnicom common stock will instead be entitled to receive, in lieu of such fractional share of Omnicom common stock, cash (rounded to the nearest cent) in an amount equal to the product of (i) the volume-weighted average closing sales prices of the Omnicom common stock on the NYSE as reported by The Wall Street Journal for the consecutive five full trading days ending on the day preceding the closing date and (ii) the fraction of a share (after taking into account all shares of IPG common stock held by the IPG stockholder immediately prior to the effective time and rounded to the nearest one-thousandth when expressed in decimal form) of Omnicom common stock that the IPG stockholder would otherwise be entitled to receive in the merger.

Background of the Merger

The following is a summary of the material events leading up to the signing of the merger agreement and the key meetings, negotiations, discussions and actions by and between IPG and Omnicom and their respective advisors that preceded the public announcement of the transaction; it does not purport to catalogue every conversation or interaction among representatives of IPG, Omnicom and other parties.

As part of Omnicom’s ongoing strategic planning process in the ordinary course of business, the Omnicom board, together with its executive management team, regularly reviews and assesses Omnicom’s business, operations, financial performance and industry conditions in light of the current business and economic environment and in consideration of Omnicom’s long-term business strategy to enhance value for its stockholders. Such reviews and assessments include periodic meetings or consultations with third-party financial, legal and other advisors. In addition, from time to time, the Omnicom board and its executive management team have evaluated and considered a variety of potential financial and strategic alternatives for Omnicom, including potential acquisitions, business combinations and other transactions, in light of industry developments and changing economic and market conditions.

As part of IPG’s ongoing strategic planning process in the ordinary course of business, the IPG board, together with its executive management team, regularly reviews and assesses IPG’s long-term strategic plans and goals, opportunities, overall industry trends, the competitive environment in which IPG operates and IPG’s short- and long-term performance. As part of these reviews, the IPG board, with the assistance of the executive management team and IPG’s advisors, considers whether various strategic actions, including business combination transactions, would be in the best interests of IPG and would enhance value for IPG stockholders

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relative to its standalone value potential. As part of these assessments, from time to time, the IPG board had authorized IPG’s executive management team to contact potential financial and strategic counterparties to discuss strategic alternatives. As leading companies in the advertising industry, each of IPG and Omnicom is generally familiar with the other’s business.

Beginning in July 2023, and consistent with the authorization of the IPG board described above, Mr. Krakowsky had a series of exploratory meetings and telephone calls with potential financial and strategic counterparties, including with Omnicom as described below, to consider what strategic alternatives may be available to IPG. These strategic alternatives included acquisitions, the sale of IPG’s digital specialist agencies and other dispositions, spin-off/split-off transactions, a third-party private investment, a take-private and various strategic business combinations. IPG’s executive management team also began to explore various internal alternatives, including restructurings, cost-savings measures and expanding IPG’s media buying offerings.

Beginning in August 2023, Mr. Krakowsky had several meetings and telephone conversations with representatives from a private equity sponsor (“Private Equity Sponsor A”) to discuss a potential strategic transaction with Private Equity Sponsor A. During such time, he also had several meetings and telephone conversations with representatives from a strategic counterparty (“Strategic Party A”) regarding a potential business combination. These discussions were preliminary in nature, and no specific transaction terms were discussed or proposed by either party. During this time, Mr. Krakowsky contacted representatives of Morgan Stanley to discuss the engagement of Morgan Stanley in connection with IPG’s review of strategic and financial alternatives.

In October 2023, IPG determined to engage Morgan Stanley to act as a financial advisor in connection with IPG’s review of strategic and financial alternatives, and IPG and Morgan Stanley entered into a customary indemnity letter. IPG’s selection of Morgan Stanley was based on its qualifications, reputation, experience, expertise and knowledge of IPG and the company’s business and industry. In December 2023, IPG and MS entered into a formal engagement letter.

On October 24 and 25, 2023, IPG held a regularly scheduled board meeting during which the IPG board conducted its annual comprehensive review of strategic matters.

On December 12, 2023, IPG received an unsolicited, preliminary non-binding proposal from Strategic Party A regarding a potential business combination between IPG and Strategic Party A, which did not specify key economic terms such as a proposed exchange ratio.

On December 14, 2023, a regularly scheduled meeting of the IPG board was held with members of IPG’s executive management team, representatives from IPG’s outside legal counsel, Willkie Farr & Gallagher LLP (“Willkie”), and representatives from Morgan Stanley in attendance. At the request of the IPG board, members of IPG’s executive management team and representatives from Morgan Stanley and the IPG board discussed various strategic alternatives for future growth and value creation, including a potential transaction with Strategic Party A, Private Equity Sponsor A and other strategic counterparties, including Omnicom. At the request of the IPG board, representatives of Willkie reviewed with the IPG board its fiduciary duties in connection with potential strategic alternatives, the current regulatory landscape and the potential execution risks associated with various strategic alternatives. After discussion, the IPG board concluded that the proposal from Strategic Party A did not merit engagement given its lack of specificity and instructed Mr. Krakowsky to convey the same to Strategic Party A, which Mr. Krakowsky did shortly thereafter.

In January 2024, Mr. Krakowsky and Mr. Wren met in person and, during that meeting, they discussed the rapidly evolving nature of the industry and adjacent sectors, as well as the factors that would drive value in media and marketing in the years to come. In February 2024, they had a telephone conversation during which they discussed exploring a potential business combination between IPG and Omnicom. In the months that followed, Mr. Krakowsky and Mr. Wren met in person several times to discuss industry dynamics and the strategic benefits

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of a potential business combination between IPG and Omnicom, including the companies’ respective capabilities, cultures and organizational structures, the complementarity of said assets, and, at a high level, potential synergies opportunities and governance considerations in a potential business combination. The discussions at that time were preliminary in nature, and no specific transaction terms were discussed or proposed by either party.

On February 15, 2024, at a regularly scheduled meeting of the Omnicom board, Omnicom’s executive management team discussed with the Omnicom board potential acquisitions, business combinations and other transactions, including a potential transaction involving IPG and Omnicom.

On February 28, 2024, following a discussion between Mr. Krakowsky and a representative of Strategic Party A, IPG received a second preliminary non-binding proposal from Strategic Party A regarding a potential business combination between IPG and Strategic Party A, which still did not specify key economic terms such as an exchange ratio. At the direction of Mr. Thomas based on the IPG board’s previous discussions, Mr. Krakowsky conveyed to the representative of Strategic Party A that the proposal did not merit engagement given its lack of specificity.

In June 2024, Mr. Krakowsky and Mr. Wren discussed more actively exploring a potential business combination between IPG and Omnicom. During this time, Omnicom discussed with PJT Partners the potential engagement of PJT Partners as financial advisor to Omnicom in connection with its review and evaluation of a potential business combination transaction with IPG. On June 7, 2024, Omnicom entered a non-disclosure agreement with PJT Partners with respect to the potential engagement. PJT Partners also subsequently provided Omnicom with a customary relationship disclosure letter regarding investment banking and other financial services provided by PJT Partners to IPG and Omnicom as well as Mr. Mark Gerstein’s role as a senior advisor to PJT Partners, noting, as is customary, that the PJT Partners deal team had been instructed to only provide information to Mr. Gerstein in his capacity as a member of the Omnicom board. Thereafter, Omnicom and PJT Partners entered into a customary indemnity letter, which was subsequently followed by entrance into a formal written engagement letter. Omnicom’s selection of PJT Partners was based on its qualifications, reputation, experience, expertise and knowledge of Omnicom and the company’s business and industry.

Throughout this time, the IPG executive management team, with the assistance of Morgan Stanley, continued to explore various other potential strategic alternatives with financial and strategic counterparties, including acquisitions, the sale of IPG’s digital specialist agencies and other dispositions, spin-off/split-off transactions, a third-party private investment, a take-private and various strategic business combinations. IPG’s executive management team also explored various internal alternatives, including restructurings and cost-savings measures. IPG’s executive management team also began to broaden its buying capability within its media practice in response to market changes. Mr. Krakowsky regularly updated the IPG board in executive sessions at regularly scheduled board meetings on the status of these various alternatives and initiatives.

On July 18, 2024, a regularly scheduled meeting of the Omnicom board was held, with members of Omnicom’s executive management team and representatives of PJT Partners and Latham & Watkins LLP (“Latham”) in attendance, to discuss a potential business combination between IPG and Omnicom, pursuant to which Omnicom would acquire IPG in an all-stock merger. At the request of the Omnicom board, Omnicom’s executive management team reviewed IPG’s business and the strategic rationale for, and potential opportunities in connection with, a potential business combination with IPG. Omnicom’s executive management team and representatives of PJT Partners reviewed IPG’s historical financial performance and the financial aspects of a potential business combination between IPG and Omnicom, based on publicly available information only. A representative of Latham then discussed certain regulatory and other legal considerations with respect to a potential transaction. The Omnicom board discussed the fact that Mr. Gerstein, a member of the Omnicom board, serves as a senior advisor to PJT Partners and is a retired partner of Latham. Mr. Gerstein confirmed that he would act solely as a director of Omnicom in connection with its consideration of such transaction and would not be involved in the potential transaction in his capacity as a senior advisor to PJT Partners and that he would not

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receive compensation from PJT Partners in connection with PJT Partners’ engagement. In connection with the potential business combination with IPG, the Omnicom board formed a transaction committee (the “Omnicom transaction committee”) consisting of Ms. Mary Choksi, Ms. Gracia Martore, Ms. Deborah Kissire and Mr. Leonard Coleman to review, evaluate, assist with the negotiations of, and make recommendations to the Omnicom board with respect to, any potential transaction. The Omnicom board retained full authority with respect to the approval and recommendation of any potential transaction.

Also in July 2024, Mr. Krakowsky and Mr. Wren again discussed a potential business combination between IPG and Omnicom, and Mr. Wren indicated that Omnicom had engaged PJT Partners as its financial advisor and Latham as its legal advisor, the Omnicom board had discussed the potential to explore a business combination between IPG and Omnicom and Omnicom was beginning to formulate a proposal to acquire IPG in a stock-for-stock transaction, which Mr. Wren expected would be an “at market” transaction. Mr. Wren said that Omnicom would still need to do a significant amount of work before it would consider making a formal proposal.

On August 5, 2024, a meeting of the Omnicom transaction committee was held with members of Omnicom’s executive management team and representatives of Latham in attendance, to review the role, responsibilities and limitations of the Omnicom transaction committee and discuss the process for and potential terms of a potential business combination between IPG and Omnicom. Mr. Wren also provided an update on his discussions with Mr. Krakowsky regarding the potential business combination transaction.

On August 9, 2024, a meeting of the Omnicom transaction committee was held with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance to discuss the process and timing for Omnicom making, and potential terms of, a non-binding proposal to IPG in respect of a potential business combination between IPG and Omnicom. At the request of the Omnicom transaction committee, members of Omnicom’s executive management team and representatives of PJT Partners reviewed recent market developments, the relative stock price performance of Omnicom and IPG and the potential impact on the financial aspects of the potential transaction. The Omnicom transaction committee decided that it would evaluate further the potential terms of a non-binding proposal and would determine whether to recommend to the Omnicom board that Omnicom submit such proposal at a special meeting of the Omnicom transaction committee expected to be held on August 12, 2024.

On August 12, 2024, a meeting of the Omnicom transaction committee was held with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance to discuss the process and timing for Omnicom making, and the potential terms of, a non-binding verbal proposal to IPG in respect of a potential business combination between IPG and Omnicom. After discussion, the Omnicom transaction committee determined to recommend to the Omnicom board that Omnicom develop and present an initial non-binding verbal proposal for an “at market” all-stock acquisition of IPG based on the then-current trading prices of IPG common stock and Omnicom common stock.

Following the meeting of the Omnicom transaction committee, on August 12, 2024, a special meeting of the Omnicom board was held with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance to discuss the process and timing for making, and the potential terms of, an initial non-binding verbal proposal to IPG in respect of a potential business combination between IPG and Omnicom. The Omnicom board reviewed recent developments regarding IPG’s business, the relative stock price performance of Omnicom and IPG and the potential impact on the financial and other aspects of the potential transaction. Representatives of Latham provided an overview of the process for, and certain anticipated business and legal terms of, a potential business combination. The Omnicom board, at the recommendation of the Omnicom transaction committee, then authorized Mr. Wren to present to Mr. Krakowsky an initial non-binding verbal proposal for an “at market” all-stock acquisition of IPG based on the then-current trading prices of IPG common stock and Omnicom common stock.

In August 2024, Mr. Krakowsky and Mr. Wren had several telephone conversations to further discuss a potential business combination, during which Mr. Krakowsky and Mr. Wren continued to discuss the strategic

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rationale for the transaction and, at a high level, potential synergies opportunities and governance considerations in a proposed business combination. In connection with these discussions, on August 13, 2024, Mr. Wren presented to Mr. Krakowsky a non-binding verbal proposal for an “at market” all-stock acquisition of IPG based on the then-current trading prices of IPG common stock and Omnicom common stock. Mr. Krakowsky subsequently informed Mr. Wren, as directed by the IPG board, that, while the IPG board understood the strategic rationale for a business combination and a stock-for-stock deal, it was not likely to support a deal without a premium for IPG’s stockholders. Mr. Krakowsky emphasized that the IPG board’s focus was on the pro forma ownership the IPG stockholders would have in a combined company. Mr. Krakowsky also informed Mr. Wren that the IPG board would consider and respond to a proposal from Omnicom if and when Omnicom delivered a formal proposal in writing. During this time, Mr. Krakowsky regularly updated the Chair of the IPG board, David Thomas, on these discussions.

In early September 2024, Mr. Krakowsky had an in-person meeting and subsequent phone call with a representative of Strategic Party A, during which the representative told Mr. Krakowsky that Strategic Party A was considering a stock-for-stock business combination between IPG and Strategic Party A but did not expect to be able to offer a premium to IPG’s stockholders. During the prior three months, Mr. Krakowsky also had several in-person, virtual and telephonic meetings with representatives of Private Equity Sponsor A, who, after discussions with potential co-sponsors, informed Mr. Krakowsky in September that it did not expect to be able to obtain the requisite financing for a strategic transaction.

On September 9, 2024, a meeting of the Omnicom transaction committee was held with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance to review Mr. Wren’s discussions with Mr. Krakowsky and to discuss whether to submit a non-binding written proposal to IPG with respect to a potential business combination. Mr. Wren noted that Mr. Krakowsky informed him that the IPG board understood the strategic rationale for a business combination between IPG and Omnicom and a stock-for-stock deal, but was unlikely to support a deal without a premium for IPG’s stockholders. At the request of the Omnicom transaction committee, members of Omnicom’s executive management team and representatives of PJT Partners reviewed recent developments regarding IPG’s business, the relative stock price performance of Omnicom and IPG and the potential impact of these developments on the other aspects of a potential business combination between IPG and Omnicom. The Omnicom transaction committee discussed the potential exchange ratios to be considered for a revised proposal to IPG, as well as a governance proposal to add two directors designated by IPG to the Omnicom board and to appoint Mr. Krakowsky as co-president and co-chief operating officer of Omnicom to serve alongside Omnicom’s current president and chief operating officer. After such discussion, the Omnicom transaction committee authorized Omnicom’s executive management team to prepare a non-binding written proposal to IPG on the terms discussed at the meeting.

On September 13, 2024, at a special meeting of the Omnicom board to discuss unrelated matters, members of Omnicom’s executive management team provided an update to the Omnicom board on recent developments related to the potential business combination between IPG and Omnicom, including that the Omnicom transaction committee had authorized Omnicom’s executive management team to prepare a non-binding written proposal that was expected to be submitted to IPG the following day, and the principal terms of such proposal.

On September 14, 2024, following a telephone discussion between Mr. Krakowsky and Mr. Wren, during which Mr. Wren previewed the terms of the proposal, Omnicom delivered to IPG an unsolicited, preliminary non-binding written proposal with respect to a potential negotiated business combination between IPG and Omnicom (the “September 14 Letter”). The September 14 Letter contemplated Omnicom acquiring all of the outstanding shares of common stock of IPG in a stock-for-stock transaction at a fixed exchange ratio of 0.330x, which represented a 6.9% premium to IPG’s closing stock price on the prior trading day and implied an approximately 38.5% pro forma ownership in the combined company by IPG’s stockholders. The September 14 Letter expressed Omnicom’s interest in further discussions regarding a potential business combination between IPG and Omnicom, citing Omnicom’s belief that the business combination would create a premier marketing and sales company that would be well-positioned to pursue new client opportunities, attract talent and deliver value

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to the companies’ respective stockholders. The September 14 Letter proposed that two current members of the IPG board would join the Omnicom board, that Mr. Wren would continue to serve as chairman and chief executive officer of the combined company, that Mr. Krakowsky would serve as co-president of the combined company (along with Omnicom’s president and chief operating officer), and that two of Omnicom’s executive vice presidents would continue to serve in their roles with other key executives of the combined company’s networks and practice areas to be determined. The September 14 Letter also advised that Omnicom had engaged Latham as its legal advisor and PJT Partners as its financial advisor in connection with the potential transaction. Mr. Krakowsky confirmed receipt of the September 14 Letter by email to Mr. Wren on September 15, 2024.

Upon receipt of the September 14 Letter, IPG’s executive management team and Mr. Thomas, with the assistance of representatives of Morgan Stanley, reviewed Omnicom’s proposal. Between September 14, 2024 and September 20, 2024, IPG’s executive management team and representatives of Morgan Stanley engaged in a number of internal discussions regarding the proposal, certain preliminary financial aspects in respect thereof and prospective next steps.

On September 20, 2024, a special meeting of the IPG board was held by videoconference with all members except Mr. Benitez and Mr. Moore present, and with members of IPG’s executive management team and representatives of Willkie and Morgan Stanley in attendance, to discuss and preliminarily evaluate the proposal in the September 14 Letter, with Mr. Krakowsky noting that a follow-up meeting would be scheduled once a more detailed evaluation was completed. Mr. Krakowsky summarized the terms of the proposal and his recent conversations with Mr. Wren and with Private Equity Sponsor A, Strategic Party A and other potential counterparties. At the request of the IPG board, a representative from Willkie reviewed the IPG board’s fiduciary duties in connection with a potential business combination transaction. Representatives of Morgan Stanley then reviewed preliminary financial aspects of a proposed business combination transaction with Omnicom. IPG’s executive management team discussed with the IPG board that it was in the process of updating its forecast for the remainder of 2024 and was accelerating its forecasting process for 2025 in light of the September 14 Letter, to assist in a more comprehensive evaluation of the proposal. The IPG board agreed with management’s recommendation and proposed next steps to meet again to consider the September 14 Letter once IPG management had completed that work. Mr. Thomas subsequently had individual conversations with each of Mr. Benitez and Mr. Moore on the matters covered during the meeting.

From September 20, 2024 until October 5, 2024, IPG’s executive management team prepared a preliminary long-range standalone plan described in the section entitled “Certain Unaudited Prospective Financial Information Prepared by IPG,” which it provided to representatives of Morgan Stanley on October 5, 2024 and presented to the IPG board on October 8, 2024. Also in October 2024, Morgan Stanley provided the IPG board with certain information regarding investment banking and other financial services provided by Morgan Stanley to IPG and Omnicom during the prior two-year period.

On October 8, 2024, a special meeting of the IPG board was held by videoconference with all members present, and with members of IPG’s executive management team and representatives of Willkie and Morgan Stanley in attendance. Representatives of IPG’s executive management team presented the IPG preliminary long-range standalone plan and summarized the various assumptions (including recent client wins and losses, the discontinuation of certain businesses, restructuring of certain businesses and certain cost-savings initiatives) and execution risks in achieving such outcomes. Representatives of IPG’s executive management team also discussed their preliminary view of potential synergies from a combination with Omnicom, which they preliminarily estimated to be between $500 to 600 million based on public information and discussions between Mr. Krakowsky and Mr. Wren. At the request of the IPG board, representatives of Morgan Stanley provided updated information on the preliminary financial aspects of IPG and a proposed business combination transaction with Omnicom, financial metrics, stock price performance and trading multiples for IPG and Omnicom as well as illustrative value creation to IPG stockholders of a combination with Omnicom. After discussion, the IPG board, while acknowledging the strategic rationale of a business combination with Omnicom, determined that the proposal in the September 14 Letter did not fully reflect IPG’s standalone prospects or the value IPG would bring

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to a combination. The IPG board also discussed that if an exchange ratio was agreed and the parties proceeded to negotiate a deal, it would be important for Mr. Krakowsky to have a meaningful role in the combined company for the benefit of various IPG stakeholders, including its stockholders, employees and clients. The IPG board instructed IPG’s executive management team to prepare, with the assistance of Morgan Stanley and Willkie, a response to the September 14 Letter stating that the exchange ratio set forth in the September 14 Letter was insufficient and to determine whether a revised offer was possible.

On October 10, 2024, at the direction of the IPG board, Mr. Krakowsky delivered IPG’s written response to the September 14 Letter to Omnicom (the “October 10 IPG Response Letter”). The October 10 IPG Response Letter stated that the IPG board agreed there was merit to a potential strategic business combination between IPG and Omnicom but that the exchange ratio proposed in the September 14 Letter did not sufficiently reflect IPG’s standalone prospects or the value IPG would bring to a combination. The October 10 IPG Response Letter stated that, as a result, the proposal would need to reflect an improved exchange ratio in order to serve as a productive basis for further discussion.

Later that day, with the prior authorization of the IPG board, Mr. Krakowsky called Mr. Wren to inform him that while the IPG board agreed there was merit to a potential strategic business combination between IPG and Omnicom, the proposed exchange ratio in the September 14 Letter would need to be improved. Mr. Krakowsky noted that until the parties were more closely aligned on the exchange ratio, the IPG board was not prepared to engage in further discussions regarding a potential transaction.

On October 15, 2024, Omnicom announced its third quarter financial results.

On October 17, 2024, a meeting of the Omnicom transaction committee was held with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance to review discussions with Mr. Krakowsky and IPG’s financial advisor regarding the September 14 Letter and the October 10 IPG Response Letter. Representatives of PJT Partners reviewed recent developments regarding the relative stock price performance of Omnicom and IPG and the potential impact of these developments on the financial aspects of the potential transaction. The Omnicom transaction committee determined to hold another meeting to discuss further a potential response to the October 10 IPG Response Letter following IPG’s third quarter announcement of its financial results.

Also on October 17, 2024, a regularly scheduled meeting of the Omnicom board was held with members of Omnicom’s executive management team. Mr. Wren provided an update on the status of negotiations with IPG and advised that the Omnicom transaction committee would be meeting to discuss a potential response to the October 10 IPG Response Letter.

On October 22, 2024, IPG announced its third quarter financial results.

On October 23 and 24, 2024, IPG held a regularly scheduled board meeting during which the IPG board conducted its annual comprehensive review of strategic matters, at which various strategic alternatives were reviewed in depth.

On October 28, 2024, a meeting of the Omnicom transaction committee was held with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance to review potential responses to the October 10 IPG Response Letter. At the request of the Omnicom board, members of Omnicom’s executive management team and representatives of PJT Partners reviewed recent developments regarding IPG’s business, including IPG’s recently announced earnings for the third quarter of 2024, the relative stock price performance of Omnicom and IPG and the potential impact of these developments on the financial aspects of the potential transaction. The participants in the meeting discussed additional terms to be included in a revised proposal, including with respect to corporate governance matters such as the name, ticker symbol and headquarters for the combined company and expectations for dividends and share repurchases between signing

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and closing. After discussion, the Omnicom transaction committee authorized Omnicom’s executive management team to make a revised proposal for a potential transaction with IPG on the terms discussed at the meeting.

On October 30, 2024, Omnicom delivered to IPG a non-binding written proposal for a strategic business combination between IPG and Omnicom (the “October 30 Letter”). The October 30 Letter reiterated Omnicom’s view as to the strong merits of a potential business combination between IPG and Omnicom and noted its belief that events subsequent to the September 14 Letter increased the attractiveness of such potential business combination, including a divergence in the companies’ respective standalone prospects as reflected in the companies’ respective stock price performance and analyst expectations. The October 30 Letter contemplated Omnicom acquiring all of the outstanding shares of IPG common stock in a stock-for-stock transaction at a fixed exchange ratio of 0.338x, which represented a 14.5% premium to IPG’s closing stock price on the prior trading day and an approximately 39.0% pro forma ownership in the combined company by IPG’s stockholders. The October 30 Letter also set forth certain other key terms of the proposal, including that the combined company would maintain Omnicom’s name, corporate headquarters and ticker symbol and the proposed treatment of dividends and share repurchases between signing and closing. The October 30 Letter stated that Omnicom was prepared to complete due diligence and finalize definitive documents quickly and that Latham was prepared to provide a draft merger agreement promptly following agreement on key terms. The October 30 Letter included a draft mutual non-disclosure agreement that included customary non-disclosure and use provisions for a period of two years and a 12-month standstill provision (which would terminate upon the occurrence of certain specified events) that prohibited each party from making unsolicited offers to acquire or acquiring the other party, and from taking certain other actions, including soliciting proxies and making any request to amend, waive or terminate the standstill provision, in each case, without the prior consent of the other party. Mr. Krakowsky and Mr. Wren also discussed the key terms of the October 30 Letter on a call that same day.

On November 5, 2024, a special meeting of the IPG board was held by videoconference with all members present, and with members of IPG’s executive management team and representatives of Morgan Stanley in attendance. At the request of the IPG board, representatives of Morgan Stanley reviewed the updated proposal contained in the October 30 Letter. Representatives of Morgan Stanley then reviewed information with respect to the preliminary financial aspects of IPG and of a proposed business combination transaction with Omnicom. After discussion, the IPG board determined that the proposed exchange ratio set forth in the October 30 Letter was still insufficient and instructed Mr. Krakowsky and representatives from Morgan Stanley to engage with Omnicom to try to achieve an enhanced proposal.

On November 6, 2024, Mr. Krakowsky informed Mr. Wren that the exchange ratio set forth in the October 30 Letter was still insufficient and they discussed whether Omnicom would be able to improve its offer.

On November 12, 2024, Latham sent Willkie an initial draft of a merger agreement reflecting the terms set forth in the October 30 Letter, as well as (a) reciprocal non-solicitation provisions that would allow either the IPG board or the Omnicom board, under certain circumstances, to change its recommendation in the event of a superior proposal or intervening event, (b) reciprocal “force-the-vote” provisions, which would prohibit either party from terminating the merger agreement to accept a superior proposal prior to a stockholder vote, (c) reciprocal termination fees equal to 3.95% of IPG’s transaction equity value, (d) a regulatory efforts covenant with a reasonable best efforts standard that provided that neither party was obligated to divest any assets to obtain regulatory approvals, (e) no antitrust reverse termination fee, (f) an outside date to be determined, (g) a construct whereby all IPG employee equity awards would roll over into Omnicom equity awards, (h) the ability of each party to grant equity and cash incentive compensation to employees subject to a cap to be agreed, (i) no increase to IPG’s regular dividend rate between signing and closing and (j) customary and generally reciprocal representations, warranties and covenants. The draft merger agreement also proposed that directors and officers from both companies would sign voting and support agreements agreeing to vote in favor of the transaction. Also on November 12, 2024, at the direction of Omnicom, representatives of PJT Partners informed representatives of Morgan Stanley that Omnicom required a list of principal issues from IPG on the merger agreement before continuing to negotiate economic terms.

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On November 13, 2024, Mr. Wren called Mr. Krakowsky to inform him that the Omnicom board would be considering IPG’s feedback on the October 30 Letter and that a subsequent proposal, reflecting Omnicom’s “best and final” offer, was expected to be forthcoming. On the same day, representatives of Latham and Willkie had an introductory call, and later Willkie provided a preliminary overview of key issues in the draft merger agreement to IPG’s executive management team and representatives of Morgan Stanley.

On November 14, 2024, representatives of Latham and Willkie had a call, following which Willkie sent a revised draft of the mutual non-disclosure agreement to Latham with an 18-month standstill. Willkie discussed on the call its preliminary views on the draft merger agreement, but did not provide a revised draft or any written comments to Latham.

On November 15, 2024, Willkie sent Latham a preliminary list of the key issues to be negotiated if the parties agreed to proceed to try to reach a definitive agreement, subject to further discussions regarding the exchange ratio. That same day, Latham sent a revised draft of the mutual non-disclosure agreement to Willkie, which included a two-year term and an 18-month standstill.

On November 16, 2024, at the direction of Omnicom, representatives of PJT Partners informed representatives of Morgan Stanley that Omnicom expected to provide IPG with a revised proposal in the near future and that the parties should enter into the mutual non-disclosure agreement prior to Omnicom providing such revised proposal.

On November 17, 2024, a meeting of the Omnicom transaction committee was held with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance to review a potential revised proposal for a strategic business combination between IPG and Omnicom. Mr. Wren provided the Omnicom transaction committee with an overview of his recent discussions with Mr. Krakowsky, including that Mr. Krakowsky explained that the IPG board required an exchange ratio higher than the exchange ratio contemplated in the October 30 Letter. Representatives of PJT Partners reviewed preliminary and illustrative exchange ratios to be considered for a revised proposal to IPG, and the Omnicom transaction committee authorized Omnicom’s executive management team to make a revised proposal for a potential business combination with IPG on the terms discussed at the meeting, as reflected in the November 18 Letter.

Also on November 17, 2024, IPG and Omnicom executed the mutual non-disclosure agreement, which included a two-year term and an 18-month standstill.

On November 18, 2024, Omnicom delivered to IPG a non-binding written proposal for a strategic business combination between IPG and Omnicom (the “November 18 Letter”). The November 18 Letter contemplated Omnicom acquiring all of the outstanding shares of common stock of IPG in a stock-for-stock transaction at a fixed exchange ratio of 0.344x, which represented a 23.0% premium to IPG’s closing stock price on the prior trading day, and approximately 39.4% pro forma ownership in the combined company by IPG’s stockholders. The November 18 Letter assumed no increase to IPG’s regular dividend rate between signing and closing. The November 18 Letter stated that the parties were aligned in their efforts to complete the transaction in the optimal manner for the combined company and expected to align the regulatory covenants in a way to best position the parties to obtain regulatory approvals. The November 18 Letter also stated that Omnicom expected the outside date to be agreed upon by the parties to provide sufficient time to allow for the regulatory process and, if necessary, potential litigation, to be completed. The November 18 Letter stated that voting and support agreements would not be required if the IPG board recommendation in favor of the transaction was unanimous. The November 18 Letter also included a reciprocal expense reimbursement on a “naked no-vote” capped at $25 million. The other terms of the proposal remained unchanged from the October 30 Letter. The November 18 Letter stated that Omnicom believed it was critical to sign and announce a transaction by December 9, 2024, to provide sufficient time to communicate with the companies’ various stakeholders prior to the year-end holiday period and that, in order to do so, the parties would need to agree on the terms outlined in the proposal that week. At the direction of Omnicom, representatives of PJT Partners reiterated to representatives of Morgan Stanley that the proposal set forth in the November 18 Letter represented Omnicom’s “best and final” offer.

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Also on November 18, 2024, a special meeting of the IPG board was held by videoconference with all members present, and with members of IPG’s executive management team and representatives of Willkie and Morgan Stanley in attendance. At the request of the IPG board, representatives of Morgan Stanley discussed with the IPG board certain preliminary financial matters relating to IPG and the proposed transaction, including the increased exchange ratio and increased implied pro forma ownership in the combined company by IPG’s stockholders contemplated by the November 18 Letter. At the request of the IPG board, representatives of Willkie discussed the proposed transaction terms as set forth in the draft merger agreement provided by Latham on November 12, 2024. The IPG board also discussed the importance of Mr. Krakowsky having a meaningful role during the integration period and in the go-forward combined company for the benefit of various IPG stakeholders, including its stockholders, employees and clients. The IPG Board also discussed with IPG’s executive management team and representatives from Morgan Stanley and Willkie whether to approach additional parties that could be interested in a potential business combination with IPG before entering into a transaction with Omnicom. In light of the comprehensive discussions Mr. Krakowsky had previously with Strategic Party A, Private Equity Sponsor A and numerous other potential financial and strategic counterparties and IPG executive management’s and Morgan Stanley’s view that it was unlikely that an alternative bidder would make a more attractive proposal within the desired timeframe and the risks of potential leaks, together with the ability of any potential interested bidder to submit a competing offer following the signing of a definitive merger agreement with Omnicom, the IPG board determined at that time to continue pursuing the transaction proposed by Omnicom without reopening discussions with any other parties. The IPG board then determined that it was willing to proceed with a transaction based on the improved exchange ratio of 0.344x set forth in the November 18 Letter and authorized Mr. Krakowsky to communicate agreement on the exchange ratio to Omnicom and for the executive management of IPG to engage in mutual due diligence and negotiate a definitive agreement, subject to the IPG board’s final approval.

On November 19, 2024, Mr. Krakowsky communicated agreement on the exchange ratio of 0.344x to Mr. Wren and a willingness to engage in mutual due diligence and progress the transaction documentation while continuing to negotiate the other open terms. Throughout that week, certain members of IPG’s executive management team, including Mr. Krakowsky, Ms. Johnson and Mr. Bonzani, met with certain members of Omnicom’s executive management team, including Mr. Wren, Mr. Angelastro, Mr. Sapollnik and Mr. Januzzi, both in New York and by videoconference, to conduct mutual business, operational, financial and legal due diligence and to discuss, among other things, the merits of, and certain potential synergies and benefits relating to, a business combination between IPG and Omnicom. During that time, IPG and Omnicom each provided access to certain confidential information regarding their respective businesses in a virtual data room accessible to a limited number of each party’s employees and representatives.

On November 21, 2024, a meeting of the Omnicom transaction committee was held with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance to provide an update on discussions between the executive management teams and advisors, as well as to discuss recent developments regarding the relative stock price performance of Omnicom and IPG and the potential impact of those developments on the financial aspects of the potential transaction.

On November 22, 2024, at the direction of the IPG board, Willkie delivered a revised draft of the merger agreement to Latham, which reflected the following key changes, which Willkie discussed with Latham via a telephone conference (a) a reciprocal right for either party to terminate the agreement and pay a termination fee to accept a “superior proposal,” (b) a termination fee payable by IPG equal to 3.0% of IPG’s transaction equity value and a termination fee payable by Omnicom equal to 3.0% of Omnicom’s transaction equity value, (d) a regulatory efforts covenant with a reasonable best efforts standard that provided that neither party was obligated to divest any assets to obtain regulatory approvals if such action would, individually or in the aggregate, result in a material adverse effect on Omnicom, IPG and their subsidiaries, taken as a whole, (e) a reverse antitrust termination fee payable by Omnicom in an amount to be determined, (f) reservation of IPG’s right to increase its regular quarterly dividend rate, (g) the conversion of IPG employee equity awards into cash-based awards at closing, consistent with the terms of the IPG equity awards, (h) the ability of IPG to implement a retention

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program with terms to be discussed and (i) for three current IPG board members to be identified prior to closing to join the combined company board at closing. The draft also removed the obligation for directors and officers to sign voting and support agreements.

On November 23, 2024, members of the executive management teams of IPG and Omnicom and IPG’s and Omnicom’s legal and financial advisors met to engage in mutual business, operational, financial and legal due diligence discussions, both in New York and by videoconference. In addition, certain members of the executive management teams of IPG and Omnicom met in New York to discuss potential synergies estimates in connection with the transaction.

On November 24, 2024, a special meeting of the Omnicom board was held, with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance. Omnicom’s executive management team provided an update to the Omnicom board on the ongoing business, operational, financial and legal due diligence meetings between the executive management teams of Omnicom and IPG and IPG’s and Omnicom’s legal and financial advisors. Members of Omnicom’s executive management team and PJT Partners then reviewed recent developments regarding IPG’s business, the relative stock price performance of Omnicom and IPG and the potential impact of these developments on the financial aspects of a potential transaction.

Throughout the weeks of November 25 and December 2, 2024, members of the executive management teams of IPG and Omnicom and IPG’s and Omnicom’s legal and financial advisors continued to engage in mutual business, operational, financial and legal due diligence meetings, both in New York and by videoconference. In addition, during this time, certain members of the executive management teams of IPG and Omnicom met in New York and by videoconference to continue to discuss potential synergies estimates in connection with the transaction.

Between November 29, 2024, and November 30, 2024, representatives of Willkie and Latham held several telephone conferences to discuss the outstanding issues in the merger agreement and remaining open legal diligence requests.

On December 3, 2024, a special meeting of the Omnicom board was held, with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance. Omnicom’s executive management team provided an update to the Omnicom board on the ongoing business, operational, financial and legal due diligence meetings between the executive management teams of Omnicom and IPG and Omnicom’s and IPG’s legal and financial advisors. Representatives of Latham reviewed the obligations of the Omnicom board under New York law when considering potential strategic transactions, including the potential strategic business combination between IPG and Omnicom, and discussed the current status of the ongoing negotiations with IPG. PJT Partners reviewed recent developments regarding IPG’s business, the relative stock price performance of Omnicom and IPG and the potential impact of these developments on the financial aspects of the potential transaction. The Omnicom board then reviewed financial projections for the fiscal years 2024 through 2029 with respect to Omnicom and IPG that were prepared by Omnicom’s executive management team and are summarized in the section entitled “Certain Unaudited Prospective Financial Information Prepared by Omnicom.” Following a discussion, the Omnicom board approved such projections for use by PJT Partners in connection with its financial analysis of the potential business combination between IPG and Omnicom. Omnicom’s executive management team also discussed the preliminary synergies estimates for the combined company that were being prepared by Omnicom’s executive management team in consultation with IPG.

During December 3, 2024 and December 4, 2024, Mr. Krakowsky and Mr. Wren had multiple discussions regarding certain open issues in the merger agreement. They agreed, among other things, that IPG would not be permitted to increase its regular dividend rate and that the termination fees would equal 3.5% of each party’s transaction equity value. Mr. Wren told Mr. Krakowsky that the Omnicom board would not agree to permit IPG to terminate the merger agreement to enter into a superior proposal prior to a stockholder meeting and vote of the IPG stockholders or obligate Omnicom to pay an antitrust termination fee, but that Omnicom was willing to

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agree to a more stringent standard regarding divestitures to obtain regulatory approval. He also told Mr. Krakowsky that the parties had a joint interest in retaining key employees and that the parties would need to further discuss that topic. He also offered Mr. Krakowsky a directorship on the post-closing Omnicom board. Finally, he acknowledged that the proposed role for Mr. Krakowsky at the combined company would not be equal to his position at IPG and could also result in a material diminution in compensation, and offered for Mr. Krakowsky to be paid, in connection with closing, the amounts payable pursuant to his outstanding IPG equity and performance cash awards, and pursuant to his executive change of control severance agreement as if Mr. Krakowsky experienced a qualifying termination following the merger.

On December 4, 2024, Mr. Thomas called Mr. Wren to express the IPG board’s strong desire for Mr. Krakowsky to have a meaningful role in integrating the two businesses and in the go-forward combined company for the benefit of IPG’s stockholders, employees and clients. Following the call, Mr. Thomas authorized Mr. Krakowsky to negotiate with Omnicom regarding Mr. Krakowsky’s potential role with the combined company.

Also on December 4, 2024, Latham delivered a revised draft of the merger agreement to Willkie which reflected the following key changes: (a) reciprocal force-the-vote provisions, (b) a termination fee equal to 3.5% of each party’s respective transaction equity value, (c) a regulatory efforts covenant with a reasonable best efforts standard that provided that neither party was obligated to divest any assets to obtain regulatory approvals if such action would, individually or in the aggregate, result in a material and adverse effect on Omnicom, IPG and their subsidiaries, taken as a whole, (d) no reverse antitrust termination fee payable by Omnicom, (e) a prohibition on IPG increasing its regular quarterly dividend rate, (f) the conversion of IPG employee equity awards into either Omnicom equity awards or cash-based awards at closing, at Omnicom’s option, (g) reservation on the ability of IPG to implement a retention program and (h) that one of the three IPG board members to join the combined company board at closing would be the current IPG chief executive officer, with the other two to be designated by IPG (and reasonably acceptable by Omnicom) prior to the consummation of the strategic business combination between IPG and Omnicom.

Also that day, members of the executive management teams of IPG and Omnicom met in New York to review and finalize the potential synergies estimates in connection with the transaction and determined that the combination should yield at least $750 million in annual run-rate synergies.

Later that day, a special meeting of the IPG board was held by videoconference with all members other than Mr. Moore present, and with members of IPG’s executive management team and representatives of Willkie and Morgan Stanley in attendance. At the request of the IPG board, IPG’s executive management team and representatives from Morgan Stanley and Willkie provided an overview of the business, financial and legal due diligence performed on Omnicom to date by IPG and its advisors and a summary of the updated transaction terms set forth in the latest draft merger agreement. After the representatives from Morgan Stanley left the meeting, representatives from Willkie presented to the IPG board its substantive antitrust assessment with respect to a potential business combination with Omnicom. Following discussion, the IPG board directed IPG’s executive management and representatives of Willkie and Morgan Stanley to continue to progress transaction documentation, due diligence and related workstreams, subject to final approval by the IPG board. Mr. Thomas subsequently updated Mr. Moore on the matters covered at the meeting.

On December 5, 2024, a special meeting of the Omnicom board was held, with members of Omnicom’s executive management team and representatives of PJT Partners and Latham in attendance. Omnicom’s executive management team provided an update to the Omnicom board on the ongoing business, operational, financial and legal due diligence meetings between executive management of Omnicom and IPG and IPG’s and Omnicom’s legal and financial advisors, as well as the status of the ongoing negotiations with IPG. Representatives of Latham provided the Omnicom board with an overview of the open issues in the merger agreement, including in respect of the treatment of IPG equity awards and benefit plans, the amount of the termination fee payable under certain circumstances set forth in the merger agreement, and regulatory efforts

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required by the parties to consummate the transaction. Representatives from Latham also presented to the Omnicom board its substantive antitrust assessment with respect to a potential business combination with IPG. Following discussion, the Omnicom board and Omnicom’s executive management team discussed updates to the preliminary synergies estimates for the combined company that had been under continued review and revision by Omnicom’s and IPG’s executive management teams. Following such discussion, the Omnicom board approved for PJT Partners’ use in connection with it financial analysis of the potential combination between IPG and Omnicom $750 million of synergies per year on a run-rate basis, as summarized in the section entitled “Certain Unaudited Prospective Financial Information Prepared by Omnicom.” At the request of the Omnicom board, representatives of PJT Partners then reviewed its preliminary and illustrative financial analysis with respect to the proposed business combination, including with respect to Omnicom’s and IPG’s respective stock prices, and explained that the proposed exchange ratio represented a 21.5% premium to the closing stock price of IPG common stock as of December 4, 2024, and a 39.4% ownership stake for IPG stockholders in the combined company. PJT Partners also confirmed that it had no additional information to disclose regarding any investment banking and other financial services provided by PJT Partners to IPG or Omnicom beyond the disclosure included in its prior relationship disclosure letter.

Also on December 5, 2024, Mr. Bonzani and representatives of Willkie had an introductory call with Mr. Krakowsky’s legal counsel, Kirkland & Ellis LLP (“Kirkland”) to discuss a process for the negotiation with Omnicom of Mr. Krakowsky’s potential role with the combined company.

Over the course of December 6 through 8, 2024, Willkie and Latham exchanged revised drafts of the merger agreement and related disclosure schedules and engaged in numerous telephonic discussions regarding the same, ultimately agreeing on terms including: (a) reciprocal force-the-vote provisions, (b) a termination fee equal to 3.25% of each party’s respective transaction equity value, (c) a regulatory efforts covenant with a reasonable best efforts standard that provided that neither party was obligated to divest any assets to obtain regulatory approvals if such action would, individually or in the aggregate, result in a material adverse effect on Omnicom and its subsidiaries, IPG and its subsidiaries, or Omnicom, IPG and their respective subsidiaries taken as a whole, (d) no reverse antitrust termination fee, (e) an initial outside date of the 12-month anniversary of the signing date, with an automatic six-month extension in order to obtain regulatory approvals, (f) the cap on employee equity awards to be granted by both parties between signing and closing, (g) a cash retention program for IPG employees and (h) IPG’s ability to implement certain cost-savings initiatives between signing and closing.

On December 6, 2024, Morgan Stanley provided the IPG board with updated information regarding the investment banking and other financial services provided by Morgan Stanley to IPG and Omnicom during the prior two-year period.

Also on December 6, 2024, Latham sent a draft term sheet to Kirkland summarizing the key terms of Mr. Krakowsky’s proposed employment with Omnicom upon the consummation of the business combination between Omnicom and IPG, which were negotiated on telephone calls between Mr. Krakowsky, Mr. Wren and representatives of Kirkland and Latham until such terms were ultimately agreed on the evening of December 7, 2024.

On December 8, 2024, a special meeting of the Omnicom board was held, with members of Omnicom’s executive management team and representatives of PJT Partners and Latham. Mr. Wren provided an update to the Omnicom board on the resolution of the business negotiations with IPG. A representative of Latham then presented and reviewed the obligations of the members of the Omnicom board under New York law in connection with the proposed transaction and materials summarizing the key provisions of the merger agreement. Omnicom’s executive management team and representatives of PJT Partners reviewed the previously authorized financial projections and synergies estimates. At the request of the Omnicom board, representatives of PJT Partners reviewed with the Omnicom board its financial analysis with respect to the proposed business combination and rendered its oral opinion, which was subsequently confirmed in a written opinion dated

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December 8, 2024, to the Omnicom board to the effect that, as of that date and based on and subject to, among other things, the assumptions made, procedures followed, matters considered and qualifications and limitations on the review undertaken by PJT Partners in connection with its opinion, the exchange ratio in the merger was fair to Omnicom from a financial point of view. Omnicom’s executive management team and representatives from PJT Partners and Latham responded to questions from the Omnicom board. Following the discussion, the Omnicom board adopted resolutions, taking into account the various matters described below under “—Recommendation of the Omnicom Board of Directors and Reasons for the Merger,” and unanimously determined that it was in the best interests of Omnicom and its stockholders, and advisable, for Omnicom to enter into the merger agreement, approved the merger agreement and the transactions contemplated thereby, including the merger, and resolved to recommend that the Omnicom stockholders vote to approve the Omnicom issuance proposal.

On December 8, 2024, the IPG board held a special meeting with all members present, and with members of IPG’s executive management team and representatives of Willkie and Morgan Stanley in attendance, to consider the proposed business combination with Omnicom. At the IPG board’s request, representatives of Morgan Stanley provided the IPG board with Morgan Stanley’s financial analysis with respect to the proposed business combination and rendered to the IPG board its oral opinion, which was subsequently confirmed by delivery of a written opinion dated December 8, 2024, that, as of such date and based upon and subject to the assumptions made, procedures followed, matters considered and qualifications and limitations on the scope of the review undertaken by Morgan Stanley in preparing its opinion, the exchange ratio pursuant to the merger agreement was fair from a financial point of view to the holders of shares of the IPG common stock (other than Omnicom or Merger Sub (or any direct or indirect wholly owned subsidiaries of IPG, Omnicom or Merger Sub)). A representative of Willkie then presented and reviewed the fiduciary duties of the members of the IPG board under Delaware law in connection with the proposed transaction and materials summarizing the key provisions of the merger agreement, which materials and merger agreement were previously provided to the IPG board. The summary term sheet for Mr. Krakowsky’s post-closing employment was also provided to the IPG board in advance of the meeting. IPG’s executive management team and representatives from Morgan Stanley and Willkie addressed questions from the IPG board. The IPG board also discussed the other strategic alternatives that it had considered over the past year. Following the discussion, the IPG board adopted resolutions, taking into account the various matters described below under “—Recommendation of the IPG Board of Directors and Reasons for the Merger,” and unanimously determined that it was in the best interests of IPG and its stockholders, and advisable, for IPG to enter into the merger agreement; approved the merger agreement and the transactions contemplated thereby, including the merger; approved that the merger agreement be submitted to the IPG stockholders and resolved to recommend that the IPG stockholders approve the merger agreement.

Later in the afternoon on December 8, 2024, the parties executed the merger agreement. Prior to the market opening on December 9, 2024, the parties issued a joint press release announcing the transaction, and shortly thereafter the parties held a joint conference call to discuss the business combination.

Recommendation of the Omnicom Board of Directors and Reasons for the Merger

By a unanimous vote at a meeting held on December 8, 2024, the Omnicom board determined that the transactions contemplated by the merger agreement, including the merger and the issuance of shares of Omnicom common stock in connection with the merger, were advisable, fair to and in the best interests of Omnicom and its stockholders, and unanimously approved, adopted and declared advisable the merger agreement and the transactions contemplated by the merger agreement, including the merger and the issuance of shares of Omnicom common stock in connection with the merger, and resolved to recommend that Omnicom stockholders approve the issuance of shares of Omnicom common stock in connection with the merger.

The Omnicom board unanimously recommends that Omnicom stockholders vote “FOR” the Omnicom issuance proposal and “FOR” the Omnicom adjournment proposal.

In the course of reaching its determinations and recommendations, the Omnicom board met multiple times and reviewed and discussed a significant amount of information and consulted with members of Omnicom’s

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senior management and Omnicom’s outside legal and financial advisors. The following are some of the

significant factors that supported the Omnicom board’s determinations and recommendation (which are presented below in no particular order and are not exhaustive):

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The Omnicom board also considered a number of uncertainties, risks and other countervailing factors in its deliberations concerning the merger and the merger agreement, including the following (which are presented below in no particular order and are not exhaustive):

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The Omnicom board considered all of these factors as a whole and unanimously determined that the transactions contemplated by the merger agreement, including the merger and the issuance of shares of Omnicom common stock in connection with the merger, were advisable, fair to and in the best interests of Omnicom and its stockholders. The foregoing discussion of the information and factors considered by the Omnicom board in reaching its conclusions and recommendation includes the principal factors considered by the Omnicom board, but is not intended to be exhaustive and may not include all of the factors considered by the Omnicom board. In view of the wide variety of factors considered by the Omnicom board in connection with its evaluation of the merger and the complexity of these matters, the Omnicom board did not consider it practical to, nor did it attempt to, quantify, rank or otherwise assign relative or specific weights to the specific factors that it considered in reaching its decision. Rather, the Omnicom board viewed its decisions as being based on the totality of the factors and information it considered. In considering the factors described above and any other factors, each individual member of the Omnicom board applied his or her own personal business judgment to the process and may have viewed factors differently or given different weight or merit to different factors.

In considering the recommendation of the Omnicom board that Omnicom stockholders vote to approve the Omnicom issuance proposal, Omnicom stockholders should be aware that the directors and executive officers of Omnicom have certain interests in the merger that may be different from, or in addition to, the interests of Omnicom stockholders generally. The Omnicom board was aware of these interests and considered them when approving the merger agreement and recommending that Omnicom stockholders vote to approve the Omnicom issuance proposal, which are described in the section entitled “—Interests of Omnicom Directors and Executive Officers in the Merger.”

The foregoing discussion of the information and factors considered by the Omnicom board is forward-looking in nature and should be read in light of the factors described in the section entitled “Cautionary Statement Regarding Forward-Looking Statements.”

Opinion of PJT Partners LP, Omnicom’s Financial Advisor

PJT Partners was retained by Omnicom to act as its financial advisor in connection with the merger and, if requested by Omnicom, to render a fairness opinion to the Omnicom board in connection therewith. Omnicom selected PJT Partners to act as its financial advisor based on PJT Partners’ qualifications, expertise and reputation, its knowledge of Omnicom’s industry and its knowledge and understanding of the business and affairs of Omnicom.

At a meeting of the Omnicom board on December 8, 2024, PJT Partners rendered its oral opinion, subsequently confirmed in its written opinion, dated December 8, 2024, to the Omnicom board to the effect that, as of the date thereof and based upon and subject to, among other things, the assumptions made, procedures followed, matters considered, and qualifications and limitations on the review undertaken by PJT Partners in connection with the opinion (which are stated in its written opinion), the exchange ratio in the merger of 0.344 shares of Omnicom common stock for each share of IPG common stock was fair to Omnicom from a financial point of view.

The full text of PJT Partners’ written opinion delivered to the Omnicom board, dated December 8, 2024, is attached as Annex B and incorporated into this joint proxy statement/prospectus by reference in its entirety. PJT Partners’ written opinion has been provided by PJT Partners at the request of the Omnicom board and is subject to, among other things, the assumptions made, procedures followed, matters considered, and qualifications and limitations on the review undertaken by PJT Partners in connection with the opinion (which are stated therein).

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You are encouraged to read the opinion carefully in its entirety. PJT Partners provided its opinion to the Omnicom board, in its capacity as its financial advisor, only in connection with and for purposes of its evaluation of the merger, and PJT Partners’ opinion does not constitute a recommendation as to any action the Omnicom board should take with respect to the merger or how any holder of Omnicom common stock or IPG common stock should vote or act with respect to the merger or any other matter. The following is a summary of PJT Partners’ opinion and the methodology that PJT Partners used to render its opinion. This summary of PJT Partners’ opinion contained in this joint proxy statement/prospectus is qualified in its entirety by reference to the full text of PJT Partners’ written opinion.

In arriving at its opinion, PJT Partners, among other things:

In preparing its opinion, with the Omnicom board’s consent, PJT Partners relied upon and assumed the accuracy and completeness of the foregoing information and all other information discussed with or reviewed by PJT Partners, without independent verification thereof. PJT Partners assumed, with the Omnicom board’s

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consent, that the Omnicom Projections for Omnicom, the Omnicom Projections for IPG and the Omnicom Synergies Estimates, and the respective assumptions underlying the Omnicom Projections for Omnicom, the Omnicom Projections for IPG and the Omnicom Synergies Estimates, and all other financial analyses, estimates and forecasts provided to PJT Partners by Omnicom management were reasonably prepared and represented Omnicom management’s best then-currently available estimates and judgments as to the business and operations and future financial performance of Omnicom and IPG, as applicable, and the other matters covered thereby. PJT Partners relied, at the direction of Omnicom, on the assessments of Omnicom management as to Omnicom’s and IPG’s respective abilities to achieve the Omnicom Projections for Omnicom, the Omnicom Projections for IPG and the Omnicom Synergies Estimates, as applicable, and assumed that the Omnicom Projections for Omnicom, the Omnicom Projections for IPG and the Omnicom Synergies Estimates would be realized in the amounts and at the times projected. PJT Partners assumed no responsibility for and expressed no opinion as to the Omnicom Projections for Omnicom, the Omnicom Projections for IPG or the Omnicom Synergies Estimates, the assumptions upon which they were based or any other financial analyses, estimates and forecasts provided to PJT Partners by Omnicom management. PJT Partners also assumed, with the Omnicom board’s consent, that there were no material changes in the assets, financial conditions, results of operations, businesses or prospects of Omnicom or IPG since the respective dates of the latest financial statements made available to PJT Partners. PJT Partners also relied, with the Omnicom board’s consent, on Omnicom management’s representations and/or projections regarding taxable income and other tax attributes of Omnicom and IPG. PJT Partners further relied, with the Omnicom board’s consent, upon the assurances of Omnicom management that they were not aware of any facts that would make the information, representations and projections provided by them inaccurate, incomplete or misleading.

PJT Partners was not asked to undertake, and did not undertake, an independent verification of any information provided to or reviewed by PJT Partners, nor was PJT Partners furnished with any such verification, and PJT Partners did not assume any responsibility or liability for the accuracy or completeness thereof. PJT Partners did not conduct a physical inspection of any of the properties or assets of Omnicom or IPG. PJT Partners did not make an independent evaluation or appraisal of the assets or the liabilities (contingent or otherwise) of Omnicom or IPG, nor was PJT Partners furnished with any such evaluations or appraisals, nor did PJT Partners evaluate the solvency of Omnicom or IPG (or the impact of the merger thereon) under any applicable laws.

PJT Partners also assumed, with the Omnicom board’s consent, that the executed merger agreement would not differ from the execution version reviewed by PJT Partners and that the consummation of the merger would be effected in accordance with the terms and conditions of the merger agreement, without waiver, modification or amendment of any material term, condition or agreement, and that, in the course of obtaining the necessary regulatory or third-party consents and approvals (contractual or otherwise) for the merger, no delay, limitation, restriction or condition would be imposed that would have an adverse effect on IPG, Omnicom or the contemplated benefits of the merger in any way that would affect PJT Partners’ opinion. PJT Partners also assumed that the representations and warranties made by Omnicom and IPG in the merger agreement and any related agreements were and would be true and correct in all respects material to its analysis. PJT Partners did not express any opinion as to any tax or other consequences that might result from the merger, nor did its opinion address any legal, tax, regulatory or accounting matters, as to which PJT Partners understood that Omnicom obtained such advice as it deemed necessary from qualified professionals. PJT Partners is not a legal, tax or regulatory advisor and relied upon, without independent verification, the assessment of Omnicom and its legal, tax and regulatory advisors with respect to such matters.

PJT Partners did not consider the relative merits of the merger as compared to any other business plan or opportunity that might be available to Omnicom or the effect of any other arrangement in which Omnicom might engage, and PJT Partners’ opinion did not address the underlying decision by Omnicom to engage in the merger. PJT Partners’ opinion was limited to the fairness as of the date of the opinion, from a financial point of view, to Omnicom of the exchange ratio in the merger, and PJT Partners’ opinion did not address any other aspect or implication of the merger, the merger agreement or any other agreement or understanding entered into or to be entered into in connection with the merger or otherwise. PJT Partners further expressed no opinion or view as to

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the fairness of the merger to the holders of any class of securities, creditors or other constituencies of any party or as to the underlying decision by Omnicom to engage in the merger. PJT Partners also expressed no opinion as to the fairness (financial or otherwise) of the amount or nature of the compensation to any officers, directors or employees, or any class of such persons of any party to the merger, whether relative to the exchange ratio or otherwise.

PJT Partners’ opinion was necessarily based upon economic, market, monetary, regulatory and other conditions as they existed and could be evaluated, and the information made available to PJT Partners, as of the date of its opinion. PJT Partners assumed no responsibility for updating or revising its opinion based on circumstances or events occurring after the date of its opinion. PJT Partners expressed no opinion as to the prices or trading ranges at which the shares of Omnicom common stock or IPG common stock will trade at any time, as to the potential effects of volatility in the credit, financial and stock markets on Omnicom, IPG or the merger or as to the impact of the merger on the solvency or viability of Omnicom or IPG or the ability of Omnicom or IPG to pay its obligations when they come due.

The issuance of PJT Partners’ opinion was approved by a fairness committee of PJT Partners in accordance with established procedures. PJT Partners’ advisory services and opinion were provided to the Omnicom board, in its capacity as its financial advisor, only in connection with and for the purposes of its evaluation of the merger, and do not constitute a recommendation as to any action the Omnicom board should take with respect to the merger or any aspect thereof. PJT Partners’ opinion does not constitute a recommendation to any holder of Omnicom common stock or IPG common stock as to how any stockholder should vote or act with respect to the merger or any other matter.

Summary of PJT Partners’ Financial Analyses

In connection with rendering its opinion, PJT Partners performed certain financial, comparative and other analyses as summarized below. In arriving at its opinion, PJT Partners did not ascribe a specific range of values to the shares of Omnicom common stock or the shares of IPG common stock but rather made its determination as to fairness, from a financial point of view, to Omnicom of the exchange ratio in the merger on the basis of various financial and comparative analyses. The preparation of a fairness opinion is a complex process and involves various determinations as to the most appropriate and relevant methods of financial and comparative analyses and the application of those methods to the particular circumstances. Therefore, a fairness opinion is not readily susceptible to summary description.

In arriving at its opinion, PJT Partners did not attribute any particular weight to any single analysis or factor considered by it but rather made qualitative judgments as to the significance and relevance of each analysis and factor relative to all other analyses and factors performed and considered by it and in the context of the circumstances of the merger. Accordingly, PJT Partners believes that its analyses must be considered as a whole, as considering any portion of such analyses and factors, without considering all analyses and factors as a whole, could create a misleading or incomplete view of the process underlying its opinion.

The following is a summary of the material financial analyses used by PJT Partners in preparing its opinion to the Omnicom board. Certain financial analyses summarized below include information presented in tabular format. In order to fully understand the financial analyses used by PJT Partners, the tables must be read together with the text of each summary, as the tables alone do not constitute a complete description of the financial analyses. In performing its analyses, PJT Partners made numerous assumptions with respect to industry performance, general business and economic conditions and other matters, many of which are beyond the control of Omnicom, IPG or any other parties to the merger. None of Omnicom, IPG, PJT Partners or any other person assumes responsibility if future results are materially different from those discussed. Any estimates contained in these analyses are not necessarily indicative of actual values or predictive of future results or values, which may be significantly more or less favorable than as set forth below. In addition, analyses relating to the value of the businesses do not purport to be appraisals or reflect the prices at which the businesses may actually be sold. The

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financial analyses summarized below were based on the Omnicom Projections for Omnicom, the Omnicom Projections for IPG, the Omnicom Synergies Estimates and other financial information prepared and furnished to PJT Partners by or on behalf of the management of Omnicom, and used at the direction of the management of Omnicom and approved for PJT Partners’ use by the Omnicom board in connection with preparing its opinion. The following summary does not purport to be a complete description of the financial analyses performed by PJT Partners. The following quantitative information, to the extent that it is based on market data, is based on market data as it existed for IPG and Omnicom as of December 6, 2024 (which was the last trading day for shares of Omnicom common stock and IPG common stock prior to the date of delivery of PJT Partners’ opinion), and is not necessarily indicative of current or future market conditions. The underlying fully diluted share count for Omnicom was provided by, and used at the direction of, Omnicom management and approved for PJT Partners’ use by the Omnicom board in connection with preparing its opinion. The underlying fully diluted share count for IPG was provided by IPG management, used at the direction of Omnicom management and approved for PJT Partners’ use by Omnicom in connection with preparing its opinion. Except as provided in “Has/Gets’ Analysis” below, all of the per share dollar amounts set forth in the summary below have been rounded to the nearest $0.05.

IPG Financial Analyses

Selected Comparable Company Analysis

PJT Partners reviewed and compared specific financial, operating and public trading data relating to IPG with similar information for three selected publicly traded advertising and marketing companies that PJT Partners deemed comparable to IPG. The selected comparable companies (which we refer to collectively as the “IPG Peers”) were Omnicom, Publicis Groupe SA (“Publicis”) and WPP plc. (“WPP”), PJT Partners reviewed and compared such data in order to assess how the public market values shares of similar publicly traded companies and to provide a range of relative implied prices per share of IPG common stock on a standalone basis, in each case by reference to these IPG Peers.

As part of its selected comparable company analysis of IPG, PJT Partners calculated and analyzed certain ratios and multiples, including (i) stock price as a multiple of estimated adjusted earnings per share for the fiscal year ending December 31, 2025 (“P/2025E Adjusted EPS”) and (ii) total enterprise value (calculated as the equity value based on fully diluted shares outstanding using the treasury stock method, plus debt, and less cash and cash equivalents, after giving effect to certain adjustments, to the extent appropriate in PJT Partners’ professional judgment, such as minority interests and earnouts and investments in affiliates) (“TEV”) as a multiple of estimated earnings before interest, taxes, depreciation and amortization, adjusted for certain other items and after subtracting stock-based compensation (“Adjusted EBITDA (post-SBC)”) for the fiscal year ending December 31, 2025 (“TEV/2025E Adjusted EBITDA (post-SBC)”).

All of these calculations (other than any such calculations based on the Omnicom Projections for IPG) were performed and based on publicly available financial data and market data (including share prices) as of the close of trading on December 6, 2024 and consensus estimates derived from sell-side research. The results of this selected comparable company analysis are summarized below:

PJT Partners, based on its professional judgment, selected the IPG Peers because PJT Partners believed their businesses and operating profiles are reasonably similar to that of IPG. However, because of the inherent

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differences between the businesses, operations and prospects of IPG and those of the IPG Peers, PJT Partners believed that it was inappropriate to, and therefore did not, rely solely on the quantitative results of the selected comparable company analysis. Accordingly, PJT Partners also made qualitative judgments concerning differences between the businesses, financial and operating characteristics and prospects of IPG and the IPG Peers that could affect the public trading values of each in order to provide a context in which to consider the results of the quantitative analysis. These qualitative judgments related primarily to the differing sizes, growth prospects, profitability levels, cash flow generation, capitalization policies and degree of operational risk between IPG and the IPG Peers.

Accordingly, PJT Partners selected a P/2025E Adjusted EPS multiple range of 10.0x to 12.0x and applied such range to IPG’s estimated adjusted earnings per share for the fiscal year ended December 31, 2025 (based on the fully diluted shares of IPG common stock outstanding, calculated using the treasury stock method, as of December 4, 2024) included in the Omnicom Projections for IPG of $2.71 per share to calculate a range of implied prices per share of IPG common stock. PJT Partners also selected a TEV/2025E Adjusted EBITDA (post-SBC) multiple range of 6.5x to 8.0x and applied such range to IPG’s estimated Adjusted EBITDA (post-SBC) for the fiscal year ending December 31, 2025 of $1.647 billion included in the Omnicom Projections for IPG to calculate a range of estimated TEV. PJT Partners then calculated a range of implied prices per share of IPG common stock by (i) subtracting IPG’s estimated debt as of December 31, 2024, which was estimated by Omnicom management to be $2.950 billion, (ii) adding IPG’s cash and cash equivalents as of December 31, 2024, which was estimated by Omnicom management to be $2.272 billion (after giving effect to the estimated net proceeds from IPG’s divestitures of R/GA and Huge), and (iii) subtracting the value of IPG’s minority investments as of December 31, 2024, which was estimated by Omnicom management to be $110 million from or to such range of estimated TEV and dividing such amount by the number of fully diluted shares of IPG common stock outstanding, using the treasury stock method, as of December 4, 2024. The following summarizes the results of these calculations:

Discounted Cash Flow Analysis

PJT Partners performed a discounted cash flow (“DCF”) analysis to estimate the present value of a share of IPG common stock (i) on a standalone basis (the “Standalone IPG DCF Analysis”) and (ii) after giving effect to the estimated annual after-tax operating expense synergies included in the Omnicom Synergies Estimates (the “Post-Synergies IPG DCF Analysis”). A DCF analysis is a traditional valuation methodology used to derive a valuation of an asset by calculating the “present value” of estimated future cash flows generated by the asset. “Present value” refers to the current value of future cash flows or amounts and is obtained by discounting those future cash flows or amounts by a discount rate that takes into account macroeconomic assumptions and estimates of risk, the opportunity cost of capital, expected returns and other appropriate factors.

Standalone IPG DCF Analysis

PJT Partners calculated the estimated TEV of IPG using the DCF method by adding (i) IPG’s estimated unlevered free cash flows for the period from January 1, 2025 through the fiscal year ending December 31, 2029 included in the Omnicom Projections for IPG to (ii) ranges of “terminal values” of IPG as of the fiscal year ending December 31, 2029, and discounted both such amounts to their present value as of December 31, 2024 using a range of selected discount rates. The unlevered free cash flows were provided by Omnicom management as part of the Omnicom Projections for IPG and were calculated by taking IPG’s estimated Adjusted EBITDA (post-SBC) and subtracting capital expenditures, change in net working capital, unlevered cash taxes, acquisitions and cash cost-to-achieve IPG’s standalone cost-saving initiatives.

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The residual value of IPG at the end of the fiscal year ending December 31, 2029, or “terminal value,” was estimated by applying a perpetuity growth rate range of 1.00% to 2.00% selected by PJT Partners in its professional judgment, to IPG’s normalized estimated unlevered free cash flow for the fiscal year ending December 31, 2029 included in the Omnicom Projections for IPG. The unlevered free cash flows and the terminal value were then discounted to present value as of December 31, 2024 using discount rates ranging from 8.75% to 9.75%, which were selected based on PJT Partners’ analysis of the weighted average cost of capital of IPG and its professional judgment.

PJT Partners then calculated a range of implied equity value per share of IPG common stock, without giving effect to any Omnicom Synergy Estimates, by (i) subtracting IPG’s debt as of December 31, 2024, which was estimated by Omnicom management to be $2.950 billion, (ii) adding IPG’s cash and cash-equivalents as of December 31, 2024, which was estimated by Omnicom management to be $2.272 billion (after giving effect to the estimated net proceeds from IPG’s divestitures of R/GA and Huge), (iii) subtracting the value of IPG’s minority investments as of December 31, 2024, which was estimated by Omnicom management to be $110 million, from or to the estimated TEV derived using the DCF method and dividing such amount by the fully diluted number of shares of IPG common stock as of December 4, 2024. The following summarizes the results of these calculations:

Post-Synergies IPG DCF Analysis

PJT Partners also estimated the present value of a share of IPG common stock after giving effect to the estimated annual after-tax operating expense synergies, net of expected transaction fees and expenses and costs to achieve such synergies, included in the Omnicom Synergies Estimates by using the DCF method (the “Net Synergies”). In performing this analysis, PJT Partners calculated the estimated annual after-tax operating expense synergies, net of transaction fees and expenses and costs to achieve such synergies, included in the Omnicom Synergy Estimates for the period from January 1, 2025 through the fiscal year ending December 31, 2029 (the “Annual Net Synergies”). The residual value of all Annual Net Synergies after the end of the fiscal year ending December 31, 2029, or terminal value, was estimated by applying a perpetuity growth rate range of 1.25% to 2.25% selected by PJT Partners in its professional judgment to the Net Synergies. The Annual Net Synergies and terminal value were then discounted to present value as of December 31, 2024 using discount rates ranging from 8.25% to 9.25%, which were selected based on PJT Partners’ analysis of the weighted average cost of capital of Omnicom and its professional judgment, which resulted in a range of present values of the Annual Net Synergies of $5.612 billion to $7.532 billion, and a present value of the Annual Net Synergies at the mid-point of such discount rates and perpetuity growth rates of $6.435 billion (the “DCF-Based Midpoint Net Synergies Value”).

Based on the DCF-Based Midpoint Net Synergies Value and the Standalone IPG DCF Analysis, PJT Partners calculated a range of implied equity value per share of IPG common stock. The following summarizes the results of these calculations:

Omnicom Financial Analyses

Selected Comparable Company Analysis

PJT Partners reviewed and compared specific financial, operating and public trading data relating to Omnicom with similar information for three selected publicly traded advertising and marketing companies that

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PJT Partners deemed comparable to Omnicom. The selected comparable companies (which we refer to collectively as the “Omnicom Peers”) were IPG, Publicis and WPP. PJT Partners reviewed and compared such data in order to assess how the public market values shares of similar publicly traded companies and to provide a range of relative implied prices per share of Omnicom common stock on a standalone basis, in each case by reference to these Omnicom Peers.

As part of its selected comparable company analysis of Omnicom, PJT Partners calculated and analyzed certain ratios and multiples, including (i) P/2025E Adjusted EPS and (ii) and TEV/2025E Adjusted EBITDA (post-SBC). All of these calculations (other than any such calculations based on the Omnicom Projections for Omnicom) were performed and based on publicly available financial data and market data (including share prices) as of the close of trading on December 6, 2024 and consensus estimates derived from sell-side research. The results of this selected comparable company analysis are summarized below:

PJT Partners, based on its professional judgment, selected the Omnicom Peers because PJT Partners believed their businesses and operating profiles are reasonably similar to that of Omnicom. However, because of the inherent differences between the businesses, operations and prospects of Omnicom and those of the Omnicom Peers, PJT Partners believed that it was inappropriate to, and therefore did not, rely solely on the quantitative results of the selected comparable company analysis. Accordingly, PJT Partners also made qualitative judgments concerning differences between the businesses, financial and operating characteristics and prospects of Omnicom and the Omnicom Peers that could affect the public trading values of each in order to provide a context in which to consider the results of the quantitative analysis. These qualitative judgments related primarily to the differing sizes, growth prospects, profitability levels, cash flow generation and degree of operational risk between Omnicom and the Omnicom Peers.

Accordingly, PJT Partners selected a P/2025E Adjusted EPS multiple range of 11.0x to 13.0x and applied such range to Omnicom’s estimated adjusted earnings per share for the fiscal year ended December 31, 2025 (based on the fully diluted shares of Omnicom common stock outstanding, calculated using the treasury stock method, as of December 4, 2024) included in the Omnicom Projections for Omnicom of $8.63 per share to calculate a range of implied prices per share of Omnicom common stock. PJT Partners also selected a TEV/2025E Adjusted EBITDA (post-SBC) multiple range of 8.0x to 9.5x and applied such range to Omnicom’s estimated Adjusted EBITDA (post-SBC) for the fiscal year ending December 31, 2025 of $2.724 billion included in the Omnicom Projections for Omnicom to calculate a range of estimated TEV. PJT Partners then calculated a range of implied prices per share of Omnicom common stock by (i) subtracting Omnicom’s debt as of December 31, 2024, which was estimated by Omnicom management to be $6.150 billion, (ii) adding Omnicom’s cash and cash-equivalents as of December 31, 2024, which was estimated by Omnicom management to be $4.485 billion, (iii) subtracting the value of Omnicom’s minority investments as of December 31, 2024, which was estimated by Omnicom management to be $1.286 billion, and (iv) adding the value of Omnicom’s investment in affiliates as of December 31, 2024, which was estimated by Omnicom management to be $66 million from or to such range of estimated TEV and dividing such amount by the number of fully diluted shares of Omnicom common stock outstanding, calculated using the treasury stock method, as of December 4, 2024. The following summarizes the results of these calculations:

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Discounted Cash Flow Analysis

PJT Partners performed a DCF analysis to estimate the present value of a share of Omnicom on a standalone basis (the “Standalone Omnicom DCF Analysis”). To calculate the estimated TEV of Omnicom using the DCF method, PJT Partners added (i) Omnicom’s estimated unlevered free cash flows for the period from January 1, 2025 through the fiscal year ending December 31, 2029 included in the Omnicom Projections for Omnicom to (ii) ranges of “terminal values” of Omnicom as of the fiscal year ending December 31, 2029, and discounted both such amounts to their present value as of December 31, 2024 using a range of selected discount rates. The unlevered free cash flows were provided by Omnicom management as part of the Omnicom Projections for Omnicom and were calculated by taking Omnicom’s estimated Adjusted EBITDA (post-SBC) and subtracting capital expenditures, change in net working capital, unlevered cash taxes and acquisitions.

The residual value of Omnicom at the end of the fiscal year ending December 31, 2029, or terminal value, was estimated by applying a perpetuity growth rate range of 1.25% to 2.25%, selected by PJT Partners in its professional judgment, to Omnicom’s normalized estimated unlevered free cash flow for the fiscal year ending December 31, 2029 included in the Omnicom Projections for Omnicom. The unlevered free cash flows and the terminal value were then discounted to present value as of December 31, 2024 using discount rates ranging from 8.25% to 9.25%, which were selected based on PJT Partners’ analysis of the weighted average cost of capital of Omnicom and its professional judgment.

PJT Partners then calculated a range of implied equity value per share of Omnicom common stock, without giving effect to any Omnicom Synergy Estimates, by (i) subtracting Omnicom’s debt as of December 31, 2024, which was estimated by Omnicom management to be $6.150 billion, (ii) adding Omnicom’s cash and cash-equivalents as of December 31, 2024, which was estimated by Omnicom management to be $4.485 billion, (iii) subtracting the value of Omnicom’s minority investments as of December 31, 2024, which was estimated by Omnicom management to be $1.286 billion, and (iv) adding the value of Omnicom’s investment in affiliates as of December 31, 2024, which was estimated by Omnicom management to be $66 million, from or to the estimated TEV derived using the DCF method and dividing such amount by the fully diluted number of shares of Omnicom common stock as of December 4, 2024. The following summarizes the results of these calculations:

Contribution Analysis

PJT Partners performed a contribution analysis in which it reviewed Omnicom’s and IPG’s respective estimated adjusted net income and estimated levered free cash flows, as provided in the Omnicom Projections for Omnicom and the Omnicom Projections for IPG, in terms of their contribution to the combined company for each fiscal year ending December 31, 2025–2029. The estimated levered free cash flows for Omnicom and IPG were calculated by taking each company’s Adjusted EBITDA (post-SBC) and adding stock-based compensation and subtracting capital expenditures, change in new working capital, net cash interest expenses and levered cash taxes. This analysis did not take into account the impact of any Omnicom Synergy Estimates. This analysis indicated (i) a range of Omnicom’s percentage contribution to the estimated adjusted net income of the combined company for such period of 62.7% to 63.2%, (ii) a range of IPG’s percentage contribution to the estimated adjusted net income of the combined company for such period of 36.8% to 37.6%, (iii) a range of Omnicom’s percentage contribution to the estimated levered free cash flows of the combined company for such period of 62.0% to 64.5% and (iv) a range of IPG’s percentage contribution to the estimated levered free cash flows of the combined company for such period of 35.5% to 38.0%.

Implied Exchange Ratio

PJT Partners calculated a range of implied exchange ratios for Omnicom common stock per share of IPG common stock based on the ranges of implied prices per share of IPG and the range of implied prices per share of

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Omnicom that were calculated by PJT Partners in its selected comparable company analyses of IPG and Omnicom, using both P/2025E Adjusted EPS and TEV/2025E Adjusted EBITDA (post-SBC), the Standalone IPG DCF Analysis and the Standalone Omnicom DCF Analysis. PJT Partners calculated the high end of the implied exchange ratio ranges by dividing the high value of the IPG implied price or equity value per share reference range for such applicable analysis by the low value of the Omnicom implied price or equity value per share reference range for each applicable analysis. PJT Partners calculated the low end of the implied exchange ratio range by dividing the low value of the IPG implied price or equity value per share reference range for each applicable analysis by the high value of the Omnicom implied price or equity value per share reference range for each applicable analysis. The result of this analysis was an implied exchange ratio range of (i) 0.242x–0.343x based on the P/2025E Adjusted EPS selected comparable company analyses, (ii) 0.228x–0.346x based on the TEV/2025E Adjusted EBITDA (post-SBC) selected comparable company analyses, and (iii) 0.206x–0.351x based on the Standalone IPG DCF Analysis and the Standalone Omnicom DCF Analysis.

PJT Partners also calculated range of implied exchange ratios for Omnicom common stock per share of IPG common stock based on the Post-Synergies IPG DCF Analysis and the Omnicom Standalone DCF Analysis. The result of this analysis was an implied exchange ratio range of 0.314x–0.544x.

“Has/Gets” Analysis

PJT Partners performed a DCF-based “Has/Gets” analysis in order to compare the DCF-based equity value per share of Omnicom on a standalone basis to the DCF-based equity value per share of the combined company, giving effect to the Net Synergies and the completion of the merger, in each case, from the perspective of the Omnicom stockholders. For purposes of the DCF-based “Has/Gets” analysis, PJT Partners calculated the equity value of the combined company, giving effect to the Net Synergies and the completion of the merger (the “DCF-Based Midpoint Combined Company Equity Value”), by adding (i) the standalone equity value of Omnicom based on PJT Partners’ Standalone Omnicom DCF Analysis at the mid-point of the discount rates and perpetuity growth rates used in such DCF analysis (the “DCF-Based Midpoint Omnicom Equity Value”), (ii) the standalone equity value of IPG based on the Standalone IPG DCF Analysis (as described above) at the mid-point of the discount rates and perpetuity growth rates used in such DCF analysis and (iii) the DCF-Based Midpoint Net Synergies Value. PJT Partners then calculated the implied price per share of Omnicom common stock on a standalone basis and the implied price per share of the combined company, giving effect to the Net Synergies and the completion of the merger, by, respectively, (i) dividing the DCF-Based Midpoint Omnicom Equity Value by the number of fully diluted shares of Omnicom common stock outstanding, calculated using the treasury stock method, as of December 4, 2024, and (ii) dividing the DCF-Based Midpoint Combined Company Equity Value by the pro forma number of outstanding shares of Omnicom common stock on a fully diluted basis, giving effect to the completion of the merger, at the exchange ratio pursuant to the merger agreement and calculated using the treasury stock method. This DCF-based “Has/Gets” analysis resulted in (i) an implied price per share of Omnicom on a standalone basis of $117.07 and (ii) an implied price per share of the combined company, giving effect to the Net Synergies and the completion of the merger, of $126.37, representing an increase in DCF-based value of approximately 7.9% in respect of a share of Omnicom common stock.

PJT Partners performed a market-based “Has/Gets” analysis in order to compare the $103.42 closing price of Omnicom common stock on December 6, 2024 to equity value per share of the combined company, giving effect to the Net Synergies and the completion of the merger, implied by the December 6, 2024 closing prices of Omnicom common stock ($103.42) and IPG common stock ($29.26), in each case, from the perspective of the Omnicom stockholders. For purposes of the market-based “Has/Gets” analysis, PJT Partners calculated the equity value of the combined company, giving effect to the Net Synergies and the completion of the merger (the “Market-Based Combined Company Value”), by adding (i) the standalone equity value of Omnicom (determined by multiplying the December 6, 2024 closing price of Omnicom common stock by the number of fully diluted shares of Omnicom common stock outstanding, calculated using the treasury stock method, as of December 4, 2024), (ii) the standalone equity value of IPG (determined by multiplying the December 6, 2024 closing price of IPG common stock by the number of fully diluted shares of IPG common stock outstanding, calculated using the

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treasury stock method, as of December 4, 2024) and (iii) the DCF-Based Midpoint Net Synergies Value. PJT Partners then calculated the implied price per share of the combined company, giving effect to the Net Synergies and the completion of the merger, by dividing the Market-Based Combined Company Value by the pro forma number of outstanding shares of Omnicom common stock on a fully diluted basis, giving effect to the completion of the merger, at the exchange ratio pursuant to the merger agreement and calculated using the treasury stock method. This marked-based “Has/Gets” analysis resulted in an implied price per share of the combined company, giving effect to the Net Synergies and the completion of the merger, of $115.58, representing an increase of approximately 11.8% relative to the December 6, 2024 closing price of Omnicom common stock.

Other Information

PJT Partners also observed the additional factors described below, which were not considered part of its financial analyses in connection with rendering its opinion, but were referenced solely for informational purposes:

PJT Partners also reviewed certain other industry transactions and advised the Omnicom board that, based on PJT Partners’ professional judgment, such transactions were of limited relevance for comparative purposes. Accordingly, PJT Partners did not perform a comparable transactions analysis.

General

The preparation of a fairness opinion is a complex process and is not necessarily susceptible to partial analysis or summary description. Selecting portions of the analyses or of the summary set forth above, without considering the analyses as a whole, could create an incomplete view of the processes underlying PJT Partners’ opinion. In arriving at its fairness determination, PJT Partners considered the results of all of its analyses and did not attribute any particular weight to any factor or analysis considered by it. Rather, PJT Partners made its determination as to fairness on the basis of its experience and professional judgment after considering the results of all of its analyses. No company used in the above-described analyses as a comparison is directly comparable to Omnicom or IPG. The terms of the merger agreement, including the exchange ratio, were determined through arm’s-length negotiations among Omnicom, IPG and Merger Sub, rather than PJT Partners, and the decision to enter into the merger agreement was solely that of Omnicom, IPG and Merger Sub.

PJT Partners prepared these analyses for purposes of providing its opinion to the Omnicom board as to the fairness, from a financial point of view, as of the date of the written opinion of PJT Partners, of the exchange

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ratio in the merger to Omnicom. These analyses do not purport to be appraisals nor do they necessarily reflect the prices at which businesses or securities actually may be sold. Analyses based upon forecasts of future results are not necessarily indicative of actual future results, which may be significantly more or less favorable than suggested by these analyses. Because these analyses are inherently subject to uncertainty, being based upon numerous factors or events beyond the control of the parties or their respective advisors, none of Omnicom, IPG, PJT Partners or any other person assumes responsibility if future results are materially different from those forecasts.

PJT Partners is an internationally recognized investment banking firm and, as part of its investment banking activities, is regularly engaged in the valuation of businesses and their securities in connection with mergers and acquisitions, investments for passive and control purposes, negotiated underwritings, competitive bids, secondary distributions of listed and unlisted securities, private placements and valuations for estate, corporate and other purposes. As a leading global M&A, capital raising, restructuring and liability management, and governance and shareholder practices advisor, PJT Partners undertakes significant client coverage efforts and has advised and/or discussed potential strategic transactions with a number of participants in Omnicom’s sector. Omnicom selected PJT Partners to act as its financial advisor because of its qualifications, reputation and experience in the valuation of businesses and securities in connection with mergers and acquisitions generally and in the advertising and marketing industry specifically.

PJT Partners is acting as financial advisor to Omnicom in connection with the merger. As compensation for its services in connection with the merger, PJT Partners is entitled to receive from Omnicom an aggregate fee of $75 million, $5 million of which became payable upon the delivery of PJT Partners’ opinion to the Omnicom board and the remainder of which is contingent and payable upon the consummation of the merger. Omnicom has also agreed to reimburse PJT Partners for out-of-pocket expenses and to indemnify PJT Partners for certain liabilities arising out of the performance of such services (including the rendering of PJT Partners’ opinion).

In the ordinary course of PJT Partners’ and its affiliates’ businesses, PJT Partners and its affiliates may provide investment banking and other financial services to Omnicom, IPG or their respective affiliates and may receive compensation for the rendering of these services. During the two years preceding the date of PJT Partners’ opinion, certain of PJT Partners’ affiliates provided corporate governance services to Omnicom unrelated to the merger, for which PJT Partners received aggregate fees of less than $1 million and may receive additional fees in the future. PJT Partners did not advise, and did not receive fees from, IPG during this period.

Recommendation of the IPG Board of Directors and Reasons for the Merger

By a unanimous vote at a meeting held on December 8, 2024, the IPG board determined that the terms of the merger agreement and the transactions contemplated by the merger agreement, including the merger, were advisable, fair to, and in the best interests of, IPG and its stockholders, and unanimously approved, authorized and adopted the merger agreement and the transactions contemplated by the merger agreement, including the merger, and resolved to recommend that the IPG stockholders adopt the merger agreement.

The IPG board unanimously recommends that IPG stockholders vote “FOR” the IPG merger proposal, “FOR” the IPG compensation proposal and “FOR” the IPG adjournment proposal.

In the course of reaching its determination and recommendation, the IPG board met many times to consider a potential transaction with Omnicom and consulted with IPG’s executive management, outside legal counsel and financial advisor. In addition, the IPG board considered a number of factors, including the following factors (which list is not exhaustive and is not necessarily presented in order of relative importance), which the IPG board viewed as being positive or favorable in coming to its determination and recommendation:

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The IPG board also considered a number of uncertainties, risks and factors it deemed generally negative or unfavorable in making its determination, approval and related recommendation, including the following (which list is not exhaustive and is not necessarily presented in order of relative importance):

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In considering the recommendation of the IPG board with respect to the IPG merger proposal, you should be aware that IPG directors and executive officers may have interests in the merger that are different from, or in addition to, yours. The IPG board was aware of and considered these interests, among other matters, in evaluating and negotiating the merger agreement, and in recommending that the merger agreement be adopted by IPG stockholders. See section entitled “—Interests of IPG Directors and Executive Officers in the Merger.”

The IPG board believed that, overall, the potential benefits of the merger to IPG stockholders outweighed the risks and uncertainties of the merger.

The foregoing discussion of factors considered by the IPG board in reaching its conclusions and recommendation includes the principal factors considered by the IPG board, but is not intended to be exhaustive and may not include all of the factors considered by the IPG board. In light of the variety of factors considered in connection with its evaluation of the merger, the IPG board did not find it practicable to, and did not, quantify or otherwise assign relative or specific weights to the specific factors considered in reaching its determinations and recommendation. Moreover, each member of the IPG board applied his or her own personal business judgment to the process and may have given different weight to different factors. The IPG board based its recommendation on the totality of the information available to it, including discussions with IPG management and outside legal and financial advisors.

It should be noted that this explanation of the reasoning of the IPG board and certain information presented in this section is forward-looking in nature and should be read in light of the factors set forth in “Cautionary Statement Regarding Forward-Looking Statements.”

Opinion of Morgan Stanley & Co. LLC, IPG’s Financial Advisor

IPG retained Morgan Stanley to act as financial advisor in connection with the review of strategic and financial alternatives by IPG and the IPG board. The IPG board selected Morgan Stanley to act as IPG’s financial advisor based on, among other things, Morgan Stanley’s qualifications, reputation, experience, expertise and its knowledge of IPG and its business and the industries in which IPG conducts its business. On December 8, 2024, Morgan Stanley rendered to the IPG board its oral opinion, which was subsequently confirmed by delivery of a written opinion dated December 8, 2024 that, as of such date and based upon and subject to the assumptions made, procedures followed, matters considered and qualifications and limitations on the scope of the review undertaken by Morgan Stanley in preparing its opinion, the exchange ratio pursuant to the merger agreement was fair from a financial point of view to IPG stockholders (other than Omnicom or Merger Sub (or any direct or indirect wholly owned subsidiaries of IPG, Omnicom or Merger Sub)).

The full text of the written opinion of Morgan Stanley, dated December 8, 2024, which sets forth, among other things, the assumptions made, procedures followed, matters considered and qualifications and limitations on the scope of review undertaken by Morgan Stanley in rendering its opinion, is included as Annex C to this document and is incorporated herein by reference in its entirety. The summary of the opinion of Morgan Stanley in this joint proxy statement/prospectus is qualified in its entirety by reference to the full text of the opinion. You are encouraged to read the opinion carefully and in its entirety. The Morgan Stanley opinion was directed to the IPG board in its capacity as such, and addressed only the fairness from a financial point of view, as of the date of such opinion, the exchange ratio pursuant to the merger agreement to IPG stockholders (other than Omnicom or Merger Sub (or any direct or indirect wholly owned subsidiaries of IPG, Omnicom or Merger Sub)). Morgan Stanley’s opinion did not in any manner address the prices at which Omnicom common stock would trade following the consummation of the merger or at any time, and Morgan Stanley expressed no opinion or recommendation as to how Omnicom stockholders or IPG stockholders should vote at the Omnicom special meeting or the IPG special meeting, respectively.

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For purposes of its opinion, Morgan Stanley:

1. Reviewed certain publicly available financial statements and other business and financial information of IPG and Omnicom, respectively;

2. Reviewed certain internal financial statements and other financial and operating data concerning IPG and Omnicom, respectively;

3. Reviewed the IPG Projections (as defined below) (for more detail see the section of this joint proxy statement/prospectus captioned “—Certain Unaudited Prospective Financial Information Prepared by IPG”), and certain financial projections with respect to IPG that were derived from a consensus of selected Wall Street equity research financial forecasts (the “IPG Street Projections”);

4. Reviewed the Omnicom Projections for Omnicom (as defined below) (for more detail see the section of this joint proxy statement/prospectus captioned “—Certain Unaudited Prospective Financial Information Prepared by Omnicom”) and certain financial projections with respect to Omnicom that were derived from a consensus of selected Wall Street equity research financial forecasts (the “Omnicom Street Projections”);

5. Reviewed information relating to certain strategic, financial and operational benefits anticipated from the merger, prepared by the management of IPG;

6. Discussed the past and current operations and financial condition and the prospects of IPG, including information relating to certain strategic, financial and operational benefits anticipated from the merger, with senior executives of IPG;

7. Discussed the past and current operations and financial condition and the prospects of Omnicom with senior executives of Omnicom;

8. Reviewed the pro forma impact of the merger on Omnicom’s earnings per share, cash flow, consolidated capitalization and certain financial ratios;

9. Reviewed the reported prices and trading activity for the IPG common stock and Omnicom common stock;

10. Compared the financial performance of IPG and Omnicom and the prices and trading activity of the IPG common stock and Omnicom common stock with that of certain other publicly-traded companies comparable with IPG and Omnicom, respectively, and their securities;

11. Reviewed the financial terms, to the extent publicly available, of certain comparable acquisition transactions;

12. Participated in certain discussions and negotiations among representatives of IPG and their legal advisors and representatives of Omnicom and their financial and legal advisors;

13. Reviewed the merger agreement and certain related documents; and

14. Performed such other analyses, reviewed such other information and considered such other factors as Morgan Stanley has deemed appropriate.

Morgan Stanley assumed and relied upon, without independent verification, the accuracy and completeness of the information that was publicly available or supplied or otherwise made available to Morgan Stanley by IPG and Omnicom, and formed a substantial basis for its opinion. With respect to the IPG Projections, the Omnicom

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Projections for Omnicom and information relating to certain strategic, financial and operational benefits anticipated from the merger, Morgan Stanley assumed that they have been reasonably prepared on bases reflecting the best currently available estimates and judgments of the respective management of IPG and Omnicom of the future financial performance of IPG and Omnicom. In addition, Morgan Stanley assumed that the merger will be consummated in accordance with the terms set forth in the merger agreement without any waiver, amendment or delay of any terms or conditions, including, among other things, that the merger will be treated as a tax-free reorganization pursuant to the Code and that the definitive merger agreement would not differ in any material respect from the draft thereof furnished to Morgan Stanley. Morgan Stanley assumed that, in connection with the receipt of all the necessary governmental, regulatory or other approvals and consents required for the proposed merger, no delays, limitations, conditions or restrictions would be imposed that would have a material adverse effect on the contemplated benefits expected to be derived in the proposed merger. Morgan Stanley is not legal, tax or regulatory advisors. Morgan Stanley is a financial advisor only and relied upon, without independent verification, the assessment of Omnicom and IPG and their legal, tax or regulatory advisors with respect to legal, tax or regulatory matters. Morgan Stanley expressed no opinion with respect to the fairness of the amount or nature of the compensation to any of IPG’s officers, directors or employees, or any class of such persons, relative to the exchange ratio applicable to IPG stockholders in the merger. Morgan Stanley did not make any independent valuation or appraisal of the assets or liabilities of IPG or Omnicom, nor was Morgan Stanley furnished with any such valuations or appraisals. Morgan Stanley’s opinion was necessarily based on financial, economic, market and other conditions as in effect on, and the information made available to Morgan Stanley as of, the date of its opinion. Events occurring after the date of its opinion may affect Morgan Stanley’s opinion and the assumptions used in preparing it, and Morgan Stanley did not assume any obligation to update, revise or reaffirm its opinion.

Summary of Material Financial Analyses

The following is a summary of the material financial analyses performed by Morgan Stanley in connection with its oral opinion and the preparation of its written opinion to the IPG board, both provided as of December 8, 2024. The following summary is not a complete description of the financial analyses performed and factors considered by Morgan Stanley in connection with its opinion, nor does the order of analyses described represent the relative importance or weight given to those analyses. Unless stated otherwise, the following quantitative information, to the extent that it is based on market data, is based on market data as of December 4, 2024, and is not necessarily indicative of current market conditions. Some of these summaries of financial analyses include information presented in tabular format. In order to fully understand the financial analyses used by Morgan Stanley, the tables must be read together with the text of each summary. The tables alone do not constitute a complete description of the financial analyses. The analyses listed in the tables and described below must be considered as a whole. Assessing any portion of such analyses and of the factors reviewed, without considering all analyses and factors, could create a misleading or incomplete view of the process underlying Morgan Stanley’s opinion. Furthermore, mathematical analysis is not in itself a meaningful method of using the data referred to below.

In performing the financial analyses summarized below and in arriving at its opinion, Morgan Stanley utilized and was directed by the IPG board to rely upon, among other matters, (i) the IPG Projections and (ii) the Omnicom Projections for Omnicom. The IPG Projections and the Omnicom Projections for Omnicom are more fully described below in the section of this joint proxy statement/prospectus captioned “The Merger—Certain Unaudited Prospective Financial Information Prepared by IPG” beginning on page 116 and “The Merger—Certain Unaudited Prospective Financial Information Prepared by Omnicom” beginning on page 113. For reference only, and not as a component of its fairness analysis, Morgan Stanley also reviewed the IPG Street Projections and Omnicom Street Projections.

Public Trading Comparables

Morgan Stanley performed a public trading comparables analysis, which is designed to provide an implied value of a company by comparing it to similar companies that are publicly traded. Morgan Stanley reviewed and

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compared certain financial estimates for each of IPG and Omnicom with comparable publicly available consensus mean equity analyst research estimates for selected companies that, in Morgan Stanley’s professional judgment, share certain similar business characteristics and have certain comparable operating characteristics including, among other things, product characteristics, similarly sized revenue and/or revenue growth rates, market capitalization, profitability, scale and/or other similar operating characteristics (which companies are referred to as the comparable companies). These companies were Publicis, WPP, IPG and Omnicom.

For purposes of this analysis, Morgan Stanley analyzed the ratio of aggregate value (“AV”), defined as market capitalization plus net debt (calculated throughout as book value of total debt less cash and cash equivalents), plus non-controlling interests, liabilities held for sale or otherwise deemed non-core, contingent acquisition consideration or deferred purchase price consideration, cross currency swaps, and underfunded pension liabilities, less assets held for sale or otherwise deemed non-core and equity method investments and other financial assets, to Adjusted EBITDA, defined as net income available to common stockholders before provision for income taxes, total (expenses) and other income, equity in net loss of unconsolidated affiliates, net income attributable to non-controlling interests, amortization of acquired intangibles, impairment of goodwill, and depreciation, estimated for calendar year 2025 (“AV/2025E Adjusted EBITDA”). To normalize AV/2025E Adjusted EBITDA for Publicis and WPP in accordance with companies that report in US GAAP, AV excluded lease liabilities in the calculation of net debt, and adjusted EBITDA was burdened by depreciation of right-of-use assets and interest paid on lease liabilities.

For purposes of this analysis, Morgan Stanley also analyzed the ratio of price per share to adjusted earnings per share (“adjusted EPS”), defined as earnings per share adjusted for amortization of acquired intangibles, restructuring charges and other adjustments, estimated for calendar year 2025 (“2025E P/E”).

The results of the public trading comparables analysis are summarized below:

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IPG Public Trading Comparables Analysis

Based on its analysis of the relevant metrics for each of the comparable companies and its professional judgment, Morgan Stanley selected reference ranges for AV/2025E Adjusted EBITDA and 2025E P/E of 7.0x – 9.6x and 9.1x – 13.0x, respectively, for IPG. Morgan Stanley applied the selected reference ranges to the adjusted EBITDA and earnings per share, each as set forth in the IPG Projections and the IPG Street Projections (for reference purposes only). Morgan Stanley’s analysis resulted in the following implied price per share ranges for IPG common stock (rounded to the nearest $0.25):

Omnicom Public Trading Comparables Analysis

Based on its analysis of the relevant metrics for each of the comparable companies and its professional judgment, Morgan Stanley selected reference ranges for AV/2025E Adjusted EBITDA and 2025E P/E of 7.0x – 9.6x and 9.1x – 13.0x, respectively, for Omnicom. Morgan Stanley applied the selected reference ranges to the adjusted EBITDA and adjusted EPS, each as set forth in the Omnicom Projections for Omnicom and the Omnicom Street Projections (for reference purposes only). Morgan Stanley’s analysis resulted in the following implied price per share ranges for Omnicom common stock (rounded to the nearest $0.25):

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Exchange Ratio Implied by Public Trading Comparables Analysis

Morgan Stanley then calculated the estimated implied exchange ratio range as set forth in the table below. Morgan Stanley divided the highest per share price for IPG common stock resulting from the application of the relevant multiples described above by the lowest per share price for Omnicom common stock resulting from the application of the relevant multiples described above to derive the highest exchange ratio implied by the public trading comparables analysis. Morgan Stanley divided the lowest per share price for IPG common stock resulting from the application of the relevant multiples described above by the highest per share price for Omnicom common stock resulting from the application of the relevant multiples described above to derive the lowest exchange ratio implied by the public trading comparables analysis. The implied exchange ratio range (rounded to three decimal places) resulting from this analysis was as follows:

Ownership Implied by Public Trading Comparables Analysis

Morgan Stanley then calculated the range of IPG’s implied equity value ownership in the combined company by (i) multiplying the fully diluted number of shares of IPG common stock, as of December 4, 2024, as provided by IPG management and calculated using the treasury stock method, with the low end and the high end of each implied exchange ratio range set out above, and then (ii) calculating the contribution of the resulting number of shares of IPG common stock to the sum of (a) such resulting number of shares of IPG common stock and (b) the fully diluted number of shares of Omnicom common stock, as of December 4, 2024, as provided by Omnicom management and calculated using the treasury stock method.

The implied IPG equity value ownership range was:

No company utilized in the public trading comparables analyses is identical to IPG or Omnicom, respectively, or directly comparable in business mix, size or other metrics. Accordingly, an analysis of the results of the foregoing analysis necessarily involves complex considerations and judgments concerning differences between IPG and Omnicom and the companies being compared and other factors that would affect the value of

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the companies to which IPG and Omnicom are being compared. In selecting comparable companies, Morgan Stanley made numerous judgments and assumptions with respect to size, business mix, industry performance, general business, regulatory, economic, market and financial conditions and other matters, many of which are beyond the control of IPG or Omnicom. These include, among other things, the impact of competition on IPG’s or Omnicom’s businesses and the industry generally, industry growth, and the absence of any adverse material change in the financial condition and prospects of IPG or Omnicom, the industry, or in the financial markets in general, which could affect the public trading value of IPG and Omnicom or the companies to which they are being compared.

Discounted Equity Value Analysis

Morgan Stanley performed a discounted equity value analysis, which is designed to provide insight into the potential future equity value of a company as a function of the company’s estimated future earnings. The resulting equity value is subsequently discounted to arrive at an estimate of the implied present value for such company’s potential future equity value. In connection with this analysis, Morgan Stanley calculated a range of implied present equity values per share on a stand-alone basis for each of IPG and Omnicom.

IPG Discounted Equity Value Analysis

To calculate the discounted equity value for IPG, Morgan Stanley utilized expected adjusted EPS for 2027 based on (i) the IPG Projections and (ii) for reference purposes only, the IPG Street Projections. Based upon the application of its professional judgment and experience after reviewing and comparing certain financial estimates for IPG, Morgan Stanley applied a range of price per share of IPG common stock to next twelve months (“NTM”) adjusted EPS (which is referred to for the purposes of this section as “NTM P/E”) of 10.0x to 12.0x to these estimates and discounted the resulting values to December 4, 2024 at a discount rate of 9.8%, which rate was selected based on the midpoint estimated cost of equity for IPG, based on the Capital Asset Pricing Model.

Based on this analysis, Morgan Stanley derived the following ranges of implied price per share of IPG common stock (rounded to the nearest $0.25):