Seres Therapeutics, Inc.

a)

Disclosure in lieu of reporting on a Current Report on Form 8-K.

Item 5.02. Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

On August 1, 2025, Paul R. Biondi submitted his resignation as a Class III director of the Company, effective August 5, 2025 (the “Effective Date”).

On August 5, 2025, the Board appointed Robert L. Rosiello to the Board as a Class III director to fill the vacancy created by Mr. Biondi’s resignation, effective as of the Effective Date. Mr. Rosiello has also been appointed to serve as a member of the Compensation and Talent Committee of the Board (the “Compensation and Talent Committee”) as of the Effective Date.

Mr. Rosiello has served as an Executive Partner at Flagship Pioneering since 2018. Prior to this, Mr. Rosiello held various positions at McKinsey & Company, a privately held management consulting firm, from 1984 to 2015, most recently serving as a Senior Partner. From July 2015 to August 2016, Mr. Rosiello served as Executive Vice President and Chief Financial Officer at Valeant Pharmaceuticals International, Inc. Mr. Rosiello currently serves on the board of directors and the audit and compensation and talent committees of Sana Biotechnology Inc. Mr. Rosiello previously served on the boards of directors of Axcella Health Inc., Evelo Biosciences, Inc., and Omega Therapeutics, Inc., each of which was a public biotechnology company during his service as a director, the Pew Research Center, a non-profit, privately held fact tank, and Inari Agriculture, Inc, a privately held agricultural biotechnology company. Mr. Rosiello received his B.A. in Economics from the University of North Carolina, where he was a Morehead Scholar and graduated Phi Beta Kappa, his M.Sc. in Economics from the London School of Economics, and his M.B.A. from Harvard Business School.

Mr. Rosiello will participate in the Company’s Non-Employee Director Compensation Program (as amended from time to time, the “Program”), which provides for, among other things, an annual retainer of $45,000 for his Board service and an additional annual retainer of $7,500 for his service as a member of the Compensation and Talent Committee. Mr. Rosiello will also receive, as an initial equity award under the terms of the Program, an option to purchase 10,000 shares of the Company’s common stock (the “Initial Award”). The Initial Award has an exercise price equal to the closing price per share of the Company’s common stock on the date of grant, and will vest and become exercisable in four substantially equal annual installments following the date of grant or in full immediately prior to the occurrence of a change in control, subject to continued service on the Board through each such vesting date.

Mr. Rosiello will also enter into the Company’s standard indemnification agreement for directors and officers.

b)

Material changes to the procedures by which security holders may recommend nominees to the board of directors.

None.

c)

Insider trading arrangements and policies.

During the three months ended June 30, 2025, no director or officer of the Company adopted orterminated a “Rule 10b5-1 trading arrangement” or “non-Rule 10b5-1 trading arrangement,” as each term is defined in Item 408(a) of Regulation S-K.