Class A Common Stock

Stagwell Inc

ONE WORLD TRADE CENTER, FLOOR 65, NEW YORK, NY, 10007

Subparts (a) and (b) of Item 5 of the Schedule 13D are hereby amended and restated as follows: Calculations of the percentage of shares of Class A Common Stock beneficially owned assume a total of 252,118,245 issued and outstanding shares of Class A Common Stock as of December 15, 2025. The aggregate number and percentage of shares of Class A Common Stock beneficially owned by each Reporting Person and, for each Reporting Person, the number of shares of Class A Common Stock as to which there is sole power to vote or to direct the vote, shared power to vote or to direct the vote, sole power to dispose or to direct the disposition, or shared power to dispose or to direct the disposition are set forth on rows 7 through 11 and row 13 of the cover pages of this Amendment No. 18 and are incorporated herein by reference. As of the date hereof, Mark J. Penn directly holds 27,368,697 shares of Class A Common Stock, of which 640,988 are unvested shares of restricted stock that are not scheduled to vest until March 1, 2026, subject to achievement of financial performance targets and continued employment. 1,750,000 shares previously held by Mark J. Penn were transferred as a gift, as described on Mr. Penn's Form 4, dated August 5, 2025. In addition, as of the date hereof, Mr. Penn directly holds (i) 191,733 restricted stock units that are not scheduled to vest until March 7, 2026, subject to continued employment (ii) 1,500,000 SARs granted on December 14, 2021 with a base price of $8.27 per share, all of which are vested and exercisable as of the date hereof and (iii) 225,000 SARs granted on March 1, 2023 with a base price of $6.79 per share, of which 150,000 are vested and exercisable as of the date hereof and 75,000 vest on March 1, 2026. Stagwell Group is the general partner and manager of Stagwell Media and is the manager of Stagwell Agency Holdings LLC, which is a subsidiary of Stagwell Media. Mark J. Penn is the controlling person of Stagwell Group. Mark J. Penn is the controlling person of Stagwell Media. To the best knowledge of the Reporting Persons, none of the individuals named in Item 2 beneficially owns any shares of Class A Common Stock except as described herein.

Subparts (a) and (b) of Item 5 of the Schedule 13D are hereby amended and restated as follows: Calculations of the percentage of shares of Class A Common Stock beneficially owned assume a total of 252,118,245 issued and outstanding shares of Class A Common Stock as of December 15, 2025. The aggregate number and percentage of shares of Class A Common Stock beneficially owned by each Reporting Person and, for each Reporting Person, the number of shares of Class A Common Stock as to which there is sole power to vote or to direct the vote, shared power to vote or to direct the vote, sole power to dispose or to direct the disposition, or shared power to dispose or to direct the disposition are set forth on rows 7 through 11 and row 13 of the cover pages of this Amendment No. 18 and are incorporated herein by reference. As of the date hereof, Mark J. Penn directly holds 27,368,697 shares of Class A Common Stock, of which 640,988 are unvested shares of restricted stock that are not scheduled to vest until March 1, 2026, subject to achievement of financial performance targets and continued employment. 1,750,000 shares previously held by Mark J. Penn were transferred as a gift, as described on Mr. Penn's Form 4, dated August 5, 2025. In addition, as of the date hereof, Mr. Penn directly holds (i) 191,733 restricted stock units that are not scheduled to vest until March 7, 2026, subject to continued employment (ii) 1,500,000 SARs granted on December 14, 2021 with a base price of $8.27 per share, all of which are vested and exercisable as of the date hereof and (iii) 225,000 SARs granted on March 1, 2023 with a base price of $6.79 per share, of which 150,000 are vested and exercisable as of the date hereof and 75,000 vest on March 1, 2026. Stagwell Group is the general partner and manager of Stagwell Media and is the manager of Stagwell Agency Holdings LLC, which is a subsidiary of Stagwell Media. Mark J. Penn is the controlling person of Stagwell Group. Mark J. Penn is the controlling person of Stagwell Media. To the best knowledge of the Reporting Persons, none of the individuals named in Item 2 beneficially owns any shares of Class A Common Stock except as described herein.

Subpart (c) of Item 5 of the Schedule 13D is hereby amended and restated as follows: No transactions in shares of Class A Common Stock were effected by any Reporting Person during the sixty days before the date hereof, except as set forth in this Amendment No. 18. Neither the filing of this Amendment No. 18 nor any of its contents shall be deemed to constitute an admission that any of the Reporting Persons is the beneficial owner of any securities covered by this statement for purposes of Section 13(d) of the Exchange Act, or for any other purpose, except to the extent of its or his pecuniary interest therein, if any, and such beneficial ownership is expressly disclaimed. The filing of this statement should not be construed to be an admission that any Reporting Person is a member of a "group" for the purposes of Sections 13(d) or 13(g) of the Exchange Act.