Form 4: Seres Co-CEO sells 76 shares under 10b5-1 plan

Thomas J. DesRosier acquired 244 shares via RSU vesting and sold 76 shares at $17.3 to cover taxes, ending with 7,623 directly owned shares and 1,665 RSUs outstanding.

Summary

• Thomas J. DesRosier (Chief Legal Officer, EVP, Co-CEO, and Co-President of Seres Therapeutics, Inc.; ticker MCRB) reported RSU vesting and a small, tax-related share sale on 11/15/2025.
• RSUs converted into 244 common shares in total on 11/15/2025 (132 shares from one RSU award and 112 shares from another).
• A sale of 76 common shares at $17.3 per share occurred on 11/15/2025 under a pre-established Rule 10b5-1 plan, solely to cover taxes related to RSU vesting.
• Direct common share ownership following the transactions is 7,623 shares.
• Remaining RSUs after the transactions: 664 units (award with initial 25% vesting on 02/15/2024) and 1,001 units (award with initial 25% vesting on 02/15/2025).
• Vesting schedules: each RSU award vests 25% on the noted start date, with the balance vesting in 12 equal quarterly installments thereafter; RSUs have no expiration date.
• The Rule 10b5-1 plan used for the sale was adopted on 03/02/2023.

Sentiment

Score: 6

Explanation: Neutral-to-slightly positive: the transaction is small, executed under a 10b5-1 plan, and explicitly for tax withholding associated with RSU vesting.

Positives

• Use of a pre-established Rule 10b5-1 plan for the sale increases transparency and reduces discretion risk.
• The share sale is small (76 shares at $17.3) and explicitly to cover taxes from RSU vesting.
• Ongoing RSU vesting aligns executive incentives with shareholders, with 1,665 RSUs outstanding post-transaction.

Negatives

• Any insider sale can be perceived negatively by the market, even when tax-related.
• RSU settlement adds incremental share issuance, creating minimal dilution.

Future Outlook

RSUs continue to vest in equal quarterly installments per the schedules beginning 02/15/2024 and 02/15/2025; no expiration dates are associated with these RSUs.

Management Comments

• Sales were effected under a Rule 10b5-1 instruction adopted on 03/02/2023 solely to cover taxes in connection with RSU vesting.
• Each RSU represents a right to receive one share of common stock; the awards vest 25% on the initial date with the remainder vesting in 12 equal quarterly installments and have no expiration date.

Industry Context

Routine insider tax-withholding sales under Rule 10b5-1 plans are common among U.S.-listed biotech companies and typically do not indicate a change in business outlook.

Comparison to Industry Standards

• Use of Rule 10b5-1 plans for tax-related sales is consistent with governance best practices seen across biotech peers.
• The very small sale size (76 shares) aligns with typical administrative transactions at companies such as Moderna, Regeneron, and CRISPR Therapeutics where executives regularly sell limited shares to satisfy withholding obligations tied to RSU vesting.

Stakeholder Impact

• Minimal market impact anticipated given the very small, tax-related sale size.
• Ongoing RSU vesting maintains executive-shareholder alignment through continued equity ownership.

Next Steps

• Continue RSU vesting per schedules (quarterly installments following 02/15/2024 and 02/15/2025).

Key Dates

Keywords

Insider transaction, Form 4, Seres Therapeutics, MCRB, Rule 10b5-1, restricted stock units, RSU vesting, tax withholding, executive compensation, insider sale, biotech