X0306 4 2020-12-01 0 0001609809 Seres Therapeutics, Inc. MCRB 0001767321 Henn Matthew R. C/O SERES THERAPEUTICS, INC. 200 SIDNEY STREET CAMBRIDGE MA 02139 0 1 0 0 See Remarks Common Stock 2020-12-01 4 M 0 26000 0.71 A 38000 D Common Stock 2020-12-01 4 M 0 26250 9.89 A 64250 D Common Stock 2020-12-01 4 M 0 27562 6.01 A 91812 D Common Stock 2020-12-01 4 S 0 55706 26.56 D 36106 D Common Stock 2020-12-01 4 S 0 26265 27.56 D 9841 D Common Stock 2020-12-01 4 S 0 9841 28.34 D 0 D Stock Option (Right to Buy) 0.71 2020-12-01 4 M 0 26000 0.00 D 2016-09-19 2024-08-06 Common Stock 26000 0 D Stock Option (Right to Buy) 9.89 2020-12-01 4 M 0 26250 0.00 D 2024-08-06 Common Stock 26250 3750 D Stock Option (Right to Buy) 6.01 2020-12-01 4 M 0 27562 0.00 D 2029-01-24 Common Stock 27562 45938 D The sale reported in the Form 4 was effected pursuant to a Rule 10b5-1 trading plan adopted by the Reporting Person on September 15, 2020. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $26.07 to $27.03, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $27.10 to $28.08, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $28.145 to $28.53, inclusive. The Reporting Person undertakes to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The option has vested as to 25% of the shares on January 26, 2018. The remainder of the shares will vest or have vested in 12 equal quarterly installments thereafter. The option has vested as to 25% of the shares on January 25, 2020. The remainder of the shares will vest or have vested in 12 equal quarterly installments thereafter. Chief Scientific Officer and EVP /s/ Thomas J. DesRosier, attorney-in-fact for Matthew R. Henn 2020-12-03