Sionna Therapeutics SEC Filings

Sionna Therapeutics filed a Form 144 notifying a proposed sale of 16,727 shares of common stock through Merrill Lynch on 10/10/2025 with an aggregate market value of $474,210.45. The shares were acquired in a private placement on 03/04/2024 and were paid for in cash. The filing also lists multiple open-market sales by affiliated funds in the prior three months, including several trades between 09/29/2025 and 10/06/2025 totaling tens of thousands of shares and gross proceeds in the low millions.

The filer certifies they know of no material nonpublic information and notes the statutory warning about false statements. The notice identifies Merrill Lynch as the broker and NASDAQ as the exchange for the planned sale.

Insider sales by a director were disclosed for Sionna Therapeutics (SION). The Form 4 shows Director Bruce Booth reported multiple sales under Rule 10b5-1 trading plans on 10/03/2025 and 10/06/2025

On 10/03/2025 the filing reports sales of 31,198 and 6,548 shares at a weighted price around $30. On 10/06/2025 it reports sales of 9,753 and 2,047 shares at a weighted price around $29.95. The reported beneficial ownership after the transactions is 2,780,301 shares held by Atlas Venture Fund XI, L.P. and 785,480 shares held by Atlas Venture Opportunity Fund II, L.P.

The filing notes the shares sold were held indirectly by the two Atlas Venture funds and that the reporting person disclaims beneficial ownership except for any pecuniary interest. The transactions were executed pursuant to trading plans adopted on 02/25/2025 and the Form is signed by an attorney-in-fact on 10/07/2025.

Sionna Therapeutics, Inc. (SION) filed a Form 144 reporting a proposed sale of 2,047 common shares through Merrill Lynch with an aggregate market value of $61,430.47. The filing lists total outstanding shares as 44,139,823, and an approximate sale date of 10/06/2025. The shares were acquired in a private placement on 03/04/2024 for cash.

The notice also discloses recent related sales by affiliated funds: Atlas Venture Opportunity Fund II and Atlas Venture Fund XI sold multiple blocks between 09/29/2025 and 10/03/2025, including a 54,637-share sale generating $1,644,065.58. The filer certifies no undisclosed material adverse information and includes the standard Rule 10b5-1 and signature attestations.

Sionna Therapeutics, Inc. (SION) filed a Form 144 notice reporting a proposed sale of 9,753 common shares valued at $292,687.53 to be sold through Merrill Lynch on 10/06/2025 on NASDAQ. The shares were acquired in a private placement on 03/04/2024 and paid for in cash.

The filing also lists recent open-market sales by related funds between 09/29/2025 and 10/03/2025, totaling approximately $3,499,940.95 across several transactions. The filer affirms no undisclosed material adverse information and includes the standard certification language regarding Rule 10b5-1 trading plans.

Sionna Therapeutics filed a Form 144 notifying a proposed sale of 31,198 common shares acquired in a private placement on 03/04/2024. The filing reports an aggregate market value of $914,101.40 and lists the approximate sale date as 10/03/2025, with Merrill Lynch named as the broker and the securities listed on NASDAQ. The company shows 44,139,823 shares outstanding. The filing also discloses recent sales by related funds in late September–early October 2025 totaling multiple transactions (largest: 54,637 shares for $1,644,065.58 on 09/29/2025).

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.