X0306 4 2016-05-06 0 0001609809 Seres Therapeutics, Inc. MCRB 0001614936 Pomerantz Roger C/O SERES THERAPEUTICS, INC. 215 FIRST STREET CAMBRIDGE MA 02142 1 1 0 0 President and CEO Common Stock 2016-05-06 4 M 0 8507 0.71 A 31234 D Common Stock 2016-05-06 4 S 0 8199 24.28 D 23035 D Common Stock 2016-05-06 4 S 0 308 25.10 D 22727 D Stock Option (right to buy) 0.71 2016-05-06 4 M 0 8507 0.00 D 2024-08-07 Common Stock 8507 1533052 D The sale reported in the Form 4 was effected pursuant to a Rule 10b5 1 trading plan adopted by the Reporting Person on February 26, 2016. The price reported is a weighted average price. These shares were sold in multiple transactions at per share prices ranging from $23.91 to $24.79. The Reporting Person undertakes to provide upon request to the SEC staff, the Issuer, or any stockholder of the Issuer, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The price reported is a weighted average price. These shares were sold in multiple transactions at per share prices ranging from $25.09 to $25.24. The Reporting Person undertakes to provide upon request to the SEC staff, the Issuer, or any stockholder of the Issuer, full information regarding the number of shares sold at each separate price within the range set forth in this footnote. The option vested as to 25% of the shares subject to the option on June 1, 2015. The remainder of the shares have vested or will vest in 12 equal quarterly installments thereafter. /s/ Eric Shaff, Attorney-in-fact 2016-05-09