Sionna Therapeutics SEC Filings

Caroline Stark Beer, Chief Business Officer of Sionna Therapeutics, Inc. (SION), was granted a non‑qualified stock option to purchase 255,000 shares of common stock with an exercise price of $28.47. The grant was reported with a transaction date of 10/01/2025 and the filing was signed on 10/03/2025. The option becomes exercisable under a vesting schedule where 25% of the shares vest on September 8, 2026, with the remaining shares vesting in 36 equal monthly installments thereafter, contingent on continued service. The option expires on 09/30/2035.

Sionna Therapeutics, Inc. (SION) filed an Initial Statement of Beneficial Ownership (Form 3) for Caroline Stark Beer, who is identified as the company's Chief Business Officer and an officer/director. The form shows the reportable event date of 10/01/2025 and is signed on 10/03/2025. The filing explicitly states: No securities are beneficially owned by the reporting person, and no non‑derivative or derivative holdings are reported.

Director Bruce Booth reported sales of 78,693 shares of Sionna Therapeutics, Inc. (SION) under Rule 10b5-1 plans. The sales occurred on 09/29/2025, 09/30/2025 and 10/01/2025 at weighted-average prices between $29.95 and $30.41, generating dispositions across two Atlas Venture funds. After the reported transactions, Atlas Venture Fund XI, L.P. is shown as beneficially owning 2,821,252 shares and Atlas Venture Opportunity Fund II, L.P. is shown as beneficially owning 794,075 shares. The filing clarifies that the reporting person is a member of the general partner entities and disclaims beneficial ownership except to the extent of any pecuniary interest.

Sionna Therapeutics filed a Form 144 reporting a proposed sale of 165 common shares acquired in a private placement on 03/04/2024. The sale is to be executed through Merrill Lynch (San Francisco) for an approximate aggregate market value of $4,852.65 with an approximate sale date of 10/01/2025. The company notes 44,139,823 shares outstanding. Related recent dispositions by affiliated funds include four sales on 09/29/2025–09/30/2025 totaling 78,493 shares for aggregate gross proceeds of $2,389,102.99.

Sionna Therapeutics (SION) filed a Form 144 reporting a proposed sale of 35 common shares through Merrill Lynch with an approximate sale date of 10/01/2025. The shares were acquired in a private placement on 03/04/2024 for cash. The filing lists 44,139,823 shares outstanding and an aggregate market value for the proposed sale of 1,029.35. The filing also discloses recent sales by affiliated funds: Atlas Venture Opportunity Fund II and Atlas Venture Fund XI executed multiple common-stock sales on 09/29/2025 and 09/30/2025, including transactions of 11,468, 2,149, 54,637, and 10,239 shares with gross proceeds reported for each sale. The notice includes the required representation that the seller is unaware of undisclosed material adverse information.

Sionna Therapeutics, Inc. (SION) Form 144 notice reports a proposed sale of 10,239 common shares through Merrill Lynch on NASDAQ with an aggregate market value of $302,255.28 and an approximate sale date of 09/30/2025. The shares were acquired in a private placement from the issuer on 03/04/2024 for cash. The filing also discloses related secondary sales on 09/29/2025: Atlas Venture Fund XI, LP sold 54,637 shares for $1,644,065.58 and Atlas Venture Opportunity Fund II, L.P. sold 11,468 shares for $345,080.15. The filer certifies no undisclosed material adverse information.

Sionna Therapeutics notice reports a proposed sale under Rule 144 of 2,149 common shares through Merrill Lynch (San Francisco) with an approximate aggregate market value of $63,438.48 and an intended sale date of 09/30/2025 on NASDAQ. The filing shows the shares were acquired on 03/04/2024 in a private placement from the issuer, paid in cash. The filing also discloses related sales in the prior three months: 11,468 shares (gross proceeds $345,080.15) by Atlas Venture Opportunity Fund II, L.P. and 54,637 shares (gross proceeds $1,644,065.58) by Atlas Venture Fund XI, LP on 09/29/2025.

Michael Cloonan, President & CEO and Director of Sionna Therapeutics, Inc. (SION), reported option exercises and concurrent sales executed under a Rule 10b5-1 trading plan adopted May 21, 2025. On 09/26/2025 he exercised 17,207 non-qualified stock options at an exercise price of $6.11 and sold 17,207 shares at a weighted average price of $28.8456, bringing beneficial ownership to 564,550 then 547,343 after the sale. On 09/29/2025 he exercised 7,793 options at $6.11 and sold 7,793 shares at a weighted average price of $29.6999, leaving total beneficial ownership at 547,343. The options vest monthly in 48 equal installments following February 2, 2022, and carry an expiration/other date listed as 03/01/2032. The Form 4 was signed by an attorney-in-fact on 09/30/2025.

Sionna Therapeutics filed a Form 144 reporting a proposed sale of common stock. The notice shows 54,637 shares to be sold through Merrill Lynch on NASDAQ, with an aggregate market value of $1,581,194.78 and approximately 44,139,823 shares outstanding. The shares were acquired in a private placement from the issuer on 03/04/2024 and paid in cash on that date. The filing states there were no securities sold by the reporting person in the past three months. The notice includes the standard representation that the seller is not aware of any undisclosed material adverse information.