X0407 4 2023-04-27 0 0001609809 Seres Therapeutics, Inc. MCRB 0001296999 Arkowitz David C/O SERES THERAPEUTICS, INC. 200 SIDNEY STREET CAMBRIDGE MA 02139 0 1 0 0 Chief Financial Officer 0 Common stock 2023-04-27 4 A 0 42500 0.00 A 166613 D On November 23, 2021, the reporting person was granted an award of 85,000 restricted stock units, which vested in the form of shares of the Issuer's common stock in two equal installments upon the satisfaction of certain performance criteria. On April 27, 2023, the Issuer's Board of Directors determined that the performance criteria for the second installment were met, resulting in the vesting and settlement of the award as to 42,500 shares. Includes 11,121 shares of common stock acquired under the Issuer's employee stock purchase plan. /s/ Thomas J. DesRosier, attorney-in-fact for David Arkowitz 2023-05-01