Thompson Peter A. 4

What Happened
Peter A. Thompson, a director of Sionna Therapeutics (SION), disposed of a total of 292,952 shares in three open-market sales on May 7, May 8 and May 11, 2026. The sales were: 48,546 shares at $44.61 ($2,165,637), 59,767 shares at $44.58 ($2,664,413), and 184,639 shares at $46.22 ($8,534,015), for aggregate proceeds of approximately $13.36 million. These sales were made pursuant to a pre-established 10b5-1 trading plan (footnote F1), which typically indicates pre-planned, routine dispositions rather than discretionary trades.

Key Details

• Transaction dates and prices:
  • 2026-05-07: 48,546 shares @ $44.61 — $2,165,637
  • 2026-05-08: 59,767 shares @ $44.58 — $2,664,413
  • 2026-05-11: 184,639 shares @ $46.22 — $8,534,015
• Total shares sold: 292,952; total proceeds: ~$13.36 million.
• Shares owned after transaction: Not specified in the provided filing excerpt.
• Footnotes of note:
  • F1: Sales were executed under a 10b5-1 plan (pre-arranged trading plan).
  • F2/F3: The shares are held of record by OrbiMed Private Investments VIII, LP; OrbiMed Advisors and its GP may be deemed to have voting/investment power. The reporting person is a member of OrbiMed Advisors; the entities disclaim beneficial ownership except to the extent of any pecuniary interest.
• Filing: Form 4 was filed on 2026-05-11; the reported transactions fall within the usual two-business-day reporting window and appear to be timely.

Context

• 10b5-1 plan trades are generally considered pre-arranged and reduce the extent to which the sale signals current insider sentiment. For retail investors, outright purchases are usually a stronger signal than routine sales.
• The filing indicates institutional record-holders (OrbiMed entities) and contains standard disclaimers about beneficial ownership; this suggests these transactions relate to managed/institutional holdings rather than a direct personal stock grant or option exercise by an individual executive.