7. Common Stock and Stock-Based Awards

On April 10, 2025, at the Company's 2025 annual meeting of stockholders (the “2025 Annual Meeting”), stockholders approved an amendment to the Company’s Restated Certificate of Incorporation in order to effect a reverse stock split of all outstanding shares of the Company's common stock. On April 21, 2025, the Company effected a 1-for-20 reverse stock split of its common stock. The reverse stock split had no impact on the number of authorized shares or the par value of preferred and common stock. As of the effective time of the reverse stock split, the number of shares of common stock issuable upon exercise, vesting or settlement of outstanding awards, the exercise price of all outstanding options and any stock price vesting goals with respect to any outstanding awards under the Company’s equity plans (including the 2025 Plan, as defined below) was proportionately adjusted (and rounded down to the nearest whole share in the case of shares and up to the nearest whole cent in the case of exercise prices, as applicable) based on the 1-for-20 ratio. In addition, the number of shares available for future issuance and any share‑based award limits under the Company’s equity plans were proportionately reduced based on the 1-for-20 ratio. Trading of the Company's common stock on The Nasdaq Global Select Market commenced on a split-adjusted basis on April 22, 2025.

Additionally, at the 2025 Annual Meeting, stockholders approved the Seres Therapeutics, Inc. 2025 Incentive Award Plan (the “2025 Plan”) as an amendment and restatement of the Seres Therapeutics, Inc. 2015 Incentive Award Plan (the “2015 Plan”). The amendment, among other things, authorized the issuance of 2,230,243 shares of the Company’s common stock for awards under the 2025 Plan, which includes 1,750,493 shares previously authorized for issuance under the 2015 Plan plus an increase of 479,750 shares (in each case, which amounts reflect the 1-for-20 reverse stock split), and extended the term of the 2025 Plan to March 3, 2035, the tenth anniversary of the approval of the 2025 Plan by the Company’s board of directors.

On May 21, 2021, the Company entered into a Sales Agreement (the “Sales Agreement”) with Cowen and Company, LLC (“Cowen”) to sell shares of the Company’s common stock, with aggregate gross sales proceeds of up to $150,000, from time to time, through an “at the market” equity offering program (“ATM”) under which Cowen acts as sales agent. During the three months ended March 31, 2026, the Company sold 25,796 shares of common stock under the Sales Agreement, at an average price of approximately $15.90 per share, raising aggregate net proceeds of approximately $400 after deducting an aggregate commission of approximately 3% and other issuance costs. During the three months ended March 31, 2025, the Company sold 54,806 shares of common stock under

the Sales Agreement, at an average price of approximately $18.60 per share, raising aggregate net proceeds of approximately $996 after deducting an aggregate commission of approximately 3% and other issuance costs.

Stock Options

The weighted average grant date fair value of stock options granted during the three months ended March 31, 2026 and 2025 was $7.79 and $13.74 per share, respectively.

During 2024, the Company granted stock options to certain executives for the purchase of an aggregate of 127,500 shares of common stock. These awards will vest only to the extent that the 30-day trailing simple average public market closing price of the Company's common stock reaches certain price thresholds. These awards have an exercise price of $22.00 and vest and become exercisable when the market conditions are satisfied or, if later, on the first anniversary of the grant date. These awards expire 10 years from the date of grant. The fair value of these market-based stock options was estimated using a Monte Carlo valuation method. During the three months ended March 31, 2026 and 2025, the Company recognized $166 and $73, respectively, of compensation expense related to these awards.

Restricted Stock Units

The Company has granted restricted stock units with service-based vesting conditions (“RSUs”) and restricted stock units with performance-based vesting conditions (“PSUs”). RSUs and PSUs represent the right to receive shares of common stock upon meeting specified vesting requirements. Restricted stock units may not be sold or transferred by the holder and vest according to the vesting conditions of each award. RSUs generally vest over four years, with 25% vesting after one year, and the remaining 75% vesting quarterly over the next 3 years, subject to continued service to the Company through the applicable vesting date. PSUs vest according to the performance requirements of the awards, generally when the Company has determined that the specified performance targets have been achieved.

During the three months ended March 31, 2026 and 2025, the Company granted 173,385 and 11,250 RSUs, respectively. During the three months ended March 31, 2026 and 2025, the Company did not grant any PSUs.

In February 2026, the Company issued retention awards to non-executive employees of the Company in the form of RSUs covering 173,385 shares of common stock with a grant date fair value of $8.74 per share. The retention RSUs will become fully vested on September 30, 2026 subject to the employee's continued employment with the Company through such date. The compensation

expense associated with these awards will be recognized ratably over the vesting period. For the three months ended March 31, 2026, the Company recognized $218 in compensation expense with respect to the retention RSUs.

Stock-based Compensation Expense