Bruce Booth - 21 Oct 2025 Form 4 Insider Report for Sionna Therapeutics, Inc. (SION)

Role
Director
Signature
/s/ Ommer Chohan, Attorney-in-Fact
Issuer symbol
SION
Transactions as of
21 Oct 2025
Net transactions value
-$3,041,683
Form type
4
Filing time
21 Oct 2025, 17:12:03 UTC
Previous filing
20 Oct 2025
Next filing
12 Dec 2025
SEC
View on sec.gov

Reporting Owners (1)

Name Relationship Address Signature Signature date CIK
Booth Bruce Director C/O SIONNA THERAPEUTICS, INC., 21 HICKORY DRIVE, SUITE 500, WALTHAM /s/ Ommer Chohan, Attorney-in-Fact 21 Oct 2025 0001451612

Transactions Table

Type Sym Class Transaction Value $ Shares Change % * Price $ Shares After Date Ownership Footnotes
transaction SION Common Stock Sale $730,262 -22,339 -0.94% $32.69 2,360,156 21 Oct 2025 By Atlas Venture Fund XI, L.P. F1, F2, F3
transaction SION Common Stock Sale $153,251 -4,688 -0.67% $32.69 697,297 21 Oct 2025 By Atlas Venture Opportunity Fund II, L.P. F2, F4, F5
transaction SION Common Stock Sale $675,639 -19,948 -0.85% $33.87 2,340,208 21 Oct 2025 By Atlas Venture Fund XI, L.P. F1, F3, F6
transaction SION Common Stock Sale $141,814 -4,187 -0.6% $33.87 693,110 21 Oct 2025 By Atlas Venture Opportunity Fund II, L.P. F4, F5, F6
transaction SION Common Stock Sale $201,186 -5,763 -0.25% $34.91 2,334,445 21 Oct 2025 By Atlas Venture Fund XI, L.P. F1, F3, F7
transaction SION Common Stock Sale $42,241 -1,210 -0.17% $34.91 691,900 21 Oct 2025 By Atlas Venture Opportunity Fund II, L.P. F4, F5, F7
transaction SION Common Stock Sale $903,921 -25,327 -1.1% $35.69 2,309,118 21 Oct 2025 By Atlas Venture Fund XI, L.P. F1, F3, F8
transaction SION Common Stock Sale $189,728 -5,316 -0.77% $35.69 686,584 21 Oct 2025 By Atlas Venture Opportunity Fund II, L.P. F4, F5, F8
transaction SION Common Stock Sale $3,023 -83 -0% $36.42 2,309,035 21 Oct 2025 By Atlas Venture Fund XI, L.P. F1, F3
transaction SION Common Stock Sale $619 -17 -0% $36.42 686,567 21 Oct 2025 By Atlas Venture Opportunity Fund II, L.P. F4, F5
* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Buy Plan / Sale Plan: These are also open market purchases/sales of shares, but in this case the transaction is part of a trading plan. Rule 10b5-1 allows insiders to setup a trading plan to buy/sell stocks over a certain period of time. Since the purchases/sales are predetermined, this protects the insiders from violating insider trading law.

Transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c).

Explanation of Responses:

Id Content
F1 This transaction was made pursuant to a Rule 10b5-1 trading plan adopted by Atlas Venture Fund XI, L.P. on February 25, 2025.
F2 The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $32.19 to $33.057 inclusive. The Reporting Persons undertake to provide to the Issuer, any security holder of the Issuer, or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares sold at each separate price within the ranges set forth in footnotes (2), (6), (7) and (8).
F3 These shares are held directly by Atlas Venture Fund XI, L.P. ("AVF XI "). The general partner of AVF XI is Atlas Venture Associates XI, L.P. ("AVA XI LP"). Atlas Venture Associates XI, LLC ("AVA XI LLC") is the general partner of AVA XI LP. The Reporting Person is a member of AVA XI LLC and disclaims beneficial ownership of such securities held by AVF XI, except to the extent of his pecuniary interest therein, if any.
F4 This transaction was made pursuant to a Rule 10b5-1 trading plan adopted by Atlas Venture Opportunity Fund II, L.P. on February 25, 2025.
F5 These shares are held directly by Atlas Venture Opportunity Fund II, L.P. ("AVOF II"). The general partner of AVOF II is Atlas Venture Associates Opportunity II, L.P. ("AVAO II LP"). Atlas Venture Associates Opportunity II, LLC ("AVAO II LLC") is the general partner of AVAO II LP. The Reporting Person is a member of AVAO II LLC and disclaims beneficial ownership of such securities held by AVOF II, except to the extent of his pecuniary interest therein, if any.
F6 The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $33.305 to $34.28 inclusive.
F7 The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $34.30 to $35.29 inclusive.
F8 The price reported in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $35.30 to $36.14 inclusive.