DesRosier Thomas 4

What Happened
Thomas DesRosier, EVP and Chief Legal Officer of Seres Therapeutics (MCRB), had restricted stock units convert to 244 shares on 2026-05-15 and immediately had those shares surrendered to cover tax obligations. He then sold 79 additional shares in an open-market sale on 2026-05-18 at $7.53 per share for proceeds of $595. The 5/15 conversions and surrender entries are recorded as derivative exercises/conversions (code M); the 5/18 sale is recorded as an open-market sale (code S).

Key Details

• Transaction dates and amounts:
  • 2026-05-15: 244 shares acquired via exercise/conversion of RSUs (recorded as M).
  • 2026-05-15: 133 shares and 111 shares disposed at $0.00 (two derivative disposition entries totaling 244 shares) — these represent share withholding for taxes.
  • 2026-05-18: 79 shares sold in the open market at $7.53 each for $595 (proceeds).
• Footnotes:
  • F1: Each restricted stock unit (RSU) converts to one share of common stock.
  • F2: The reported sales were effected under a Rule 10b5-1 plan (adopted Mar 2, 2023) and were made solely to cover taxes arising from RSU vesting.
  • F3/F4: RSUs vest on a schedule (25% vested Feb 15, 2024 and Feb 15, 2025, with the remainder vesting in 12 equal quarterly installments); RSUs have no expiration.
• Shares owned after transaction: Not specified in the filing.
• Timeliness: Form 4 filed 2026-05-19 reporting transactions on 2026-05-15 and 2026-05-18. The 5/15 entries were reported four days later than the transaction date, which exceeds the typical two-business-day Form 4 reporting window.

Context

• These filings reflect RSU vesting and routine tax-related actions (conversion of RSUs and share withholding/sales to cover taxes). The derivative entries indicate conversion/settlement of RSUs rather than a cash purchase.
• The 10b5-1 plan note clarifies the sale was prearranged to handle tax obligations; such planned sales are common and do not necessarily signal a change in an insider’s view of the company.