ORBIMED ADVISORS LLC 4

What Happened
OrbiMed Advisors LLC (reported as a director-related reporting person) sold 85,918 shares of Sionna Therapeutics, Inc. (SION) on July 7, 2026. The shares were disposed at $44.86 each, generating proceeds of approximately $3,854,281. The filing classifies the transaction as an open-market or private sale and notes the sale occurred pursuant to a 10b5-1 trading plan.

Key Details

• Transaction date: 2026-07-07; Filing date: 2026-07-09 (appears to be filed within the typical two-business-day Form 4 window).
• Price and quantity: 85,918 shares sold at $44.86 per share; total proceeds ≈ $3,854,281.
• Method: Open market or private sale executed pursuant to a 10b5-1 plan (Footnote F1).
• Ownership structure: The shares are held of record by OrbiMed Private Investments VIII, LP (OPI VIII); OrbiMed Advisors and GP VIII are related entities that may be deemed to have voting/investment power (Footnote F2). The report is jointly filed; reporting persons disclaim beneficial ownership except for any pecuniary interest (Footnote F3).
• Shares owned after transaction: Not specified in the provided excerpt of the filing.

Context
This was a sale by an institutional reporting entity rather than a direct personal purchase by an individual executive. Sales under pre-established 10b5-1 plans are commonly scheduled in advance and are often considered routine disposition rather than a direct signal of management sentiment. Retail investors should view this as a supply-side transaction by an institutional holder; it does not, by itself, indicate company performance or insider confidence.