X0306 4 2022-06-15 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 Common stock 2022-06-15 4 M 0 5000 0.00 A 70492 D Common stock 2022-10-27 4 A 0 42500 0.00 A 112992 D Restricted Stock Units 2022-06-15 4 M 0 5000 0.00 D Common Stock 5000 0 D On November 23, 2021, the reporting person was granted an award of 85,000 restricted stock units, which vest in the form of shares of the Issuer's common stock in two equal installments upon the satisfaction of certain performance criteria. On October 27, 2022, the Issuer's Board of Directors determined that the performance criteria for the first installment were met, resulting in the vesting and settlement of the award as to 42,500 shares. Each restricted stock unit represents a contingent right to receive one share of Issuer common stock. On June 1, 2021, the reporting person was granted an award of restricted stock units, 100% of which vested and settled on June 15, 2022. /s/ Thomas J. DesRosier, attorney-in-fact for David Arkowitz 2022-10-31