Seres (MCRB) EVP & Chief Legal Officer DesRosier Sells 82 Shares

What Happened

• Thomas DesRosier, EVP and Chief Legal Officer of Seres Therapeutics (MCRB), had 245 restricted stock units convert to 245 shares on Aug 15, 2026 (reported as exercise/conversion of a derivative). Of those, 133 and 112 shares were withheld/settled (reported as derivative dispositions at $0) to satisfy tax obligations. On Aug 17, 2026 she sold 82 shares in an open-market transaction at $4.55 per share, generating $373. This was a sale (routine/tax-related), not a purchase.

Key Details

• Transaction dates and prices:
  • 2026-08-15: 245 RSUs converted to 245 shares (exercise/conversion, reported as derivative).
  • 2026-08-15: 133 shares and 112 shares reported as disposed at $0 (derivative withholding/settlement for taxes).
  • 2026-08-17: Open-market sale of 82 shares at $4.55 each for $373.
• Shares owned after transaction: Not stated in the filing.
• Footnotes of note:
  • F1: Each RSU equals a contingent right to one share.
  • F2: The Aug 17 sale was effected under a Rule 10b5-1 plan adopted Mar 2, 2023, and was made solely to cover taxes from RSU vesting.
  • F3/F4: RSU vesting schedule: 25% vested Feb 15, 2024 and Feb 15, 2025, with the remainder vesting/settling in 12 equal quarterly installments; RSUs have no expiration.
• Filing/timeliness: Form 4 filed Aug 18, 2026 (Report period Aug 15, 2026). The filing appears timely (no late-filing flag).

Context

• These transactions reflect RSU vesting with shares withheld/settled to cover taxes and a small supplemental open-market sale under a pre-existing 10b5-1 plan. The cash amount ($373) is small and consistent with tax-covering activity rather than a directional bet on the stock. The derivative entries (code M) indicate conversion/settlement of equity awards rather than option exercises for cash.