X0508 4 2025-11-15 0001609809 Seres Therapeutics, Inc. MCRB 0001643734 Shaff Eric D. C/O SERES THERAPEUTICS, INC. 101 CAMBRIDGE PARK DRIVE CAMBRIDGE MA 02140 true false false false true Common Stock 2025-11-15 4 M false 390 A 10999 D Common Stock 2025-11-15 4 M false 331 A 11330 D Common Stock 2025-11-15 4 S false 217 17.30 D 11113 D Restricted Stock Units 2025-11-15 4 M false 390 0 D Common Stock 390 1954 D Restricted Stock Units 2025-11-15 4 M false 331 0 D Common Stock 331 2989 D Each restricted stock unit represents a contingent right to receive one share of Issuer common stock. The sales reported in this Form 4 were effected pursuant to a Rule 10b5-1 instruction adopted by the reporting person on March 2, 2023, solely with the intent to cover taxes in connection with the vesting of the restricted stock units. The restricted stock units vested and settled as to 25% of the restricted stock units on February 15, 2024. The remainder of the restricted stock units have vested and settled or will vest and settle in 12 equal quarterly installments thereafter. The restricted stock units have no expiration date. The restricted stock units vested and settled as to 25% of the restricted stock units on February 15, 2025. The remainder of the restricted stock units have vested and settled or will vest and settle in 12 equal quarterly installments thereafter. The restricted stock units have no expiration date. /s/ Thomas J. DesRosier, attorney-in-fact for Eric D. Shaff 2025-11-18