On, October 22, 2026, Seres Therapeutics' CFO Marella Thorell Resigned Effective November 15, 2026

On October 22, 2026, Marella Thorell, Executive Vice President and Chief Financial Officer of Seres Therapeutics, Inc. (the "Company"), resigned from her positions as Executive Vice President and Chief Financial Officer of the Company, effective November 15, 2026 (the "Effective Date"). Following the Effective Date, Ms. Thorell is expected to provide advisory services to the Company to support an orderly transition, on terms to be agreed between Ms. Thorell and the Company.