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

Reporting relationship: Director
Issuer ticker: SION
Reported as of: 21 Oct 2025
Net transaction value: -$3,041,683
SEC form: 4
Accepted by SEC: 21 Oct 2025, 17:12:03 UTC
Prior SEC filing: 20 Oct 2025
Next SEC filing: 12 Dec 2025
Source filing: View source filing
Reporting owner signature: /s/ Ommer Chohan, Attorney-in-Fact

Key filing fact

Bruce Booth filed Form 4 for Sionna Therapeutics, Inc. (SION) on 21 Oct 2025.

Key facts

This page summarizes Bruce Booth's Form 4 filing for Sionna Therapeutics, Inc. (SION).
10 reported transactions and 0 derivative rows are listed below.
Accepted by SEC: 21 Oct 2025, 17:12.

Change

Previous filing in this sequence was filed on 20 Oct 2025.
Current net transaction value: -$3,041,683.

Research use

This tells you what this filing adds before you inspect full transaction and derivative tables.
You can trace every row back to the original SEC filing document.

Evidence

Filed on Form 4

Ownership activity is grounded in SEC Form 4 disclosures.

View source filing

Reporting Owners (1)

CIK 0001451612 Primary reporting owner

Booth Bruce

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

Reported non-derivative transactions

Shares, units, or other non-derivative securities reported in this filing.

SION transaction

Common Stock

Sale

Transaction value: $730,262
Shares: -22,339
Change %: -0.94%
Price: $32.69
Shares after: 2,360,156
Date: 21 Oct 2025
Ownership: By Atlas Venture Fund XI, L.P.
Footnotes: F1, F2, F3

SION transaction

Common Stock

Sale

Transaction value: $153,251
Shares: -4,688
Change %: -0.67%
Price: $32.69
Shares after: 697,297
Date: 21 Oct 2025
Ownership: By Atlas Venture Opportunity Fund II, L.P.
Footnotes: F2, F4, F5

SION transaction

Common Stock

Sale

Transaction value: $675,639
Shares: -19,948
Change %: -0.85%
Price: $33.87
Shares after: 2,340,208
Date: 21 Oct 2025
Ownership: By Atlas Venture Fund XI, L.P.
Footnotes: F1, F3, F6

SION transaction

Common Stock

Sale

Transaction value: $141,814
Shares: -4,187
Change %: -0.6%
Price: $33.87
Shares after: 693,110
Date: 21 Oct 2025
Ownership: By Atlas Venture Opportunity Fund II, L.P.
Footnotes: F4, F5, F6

SION transaction

Common Stock

Sale

Transaction value: $201,186
Shares: -5,763
Change %: -0.25%
Price: $34.91
Shares after: 2,334,445
Date: 21 Oct 2025
Ownership: By Atlas Venture Fund XI, L.P.
Footnotes: F1, F3, F7

SION transaction

Common Stock

Sale

Transaction value: $42,241
Shares: -1,210
Change %: -0.17%
Price: $34.91
Shares after: 691,900
Date: 21 Oct 2025
Ownership: By Atlas Venture Opportunity Fund II, L.P.
Footnotes: F4, F5, F7

SION transaction

Common Stock

Sale

Transaction value: $903,921
Shares: -25,327
Change %: -1.1%
Price: $35.69
Shares after: 2,309,118
Date: 21 Oct 2025
Ownership: By Atlas Venture Fund XI, L.P.
Footnotes: F1, F3, F8

SION transaction

Common Stock

Sale

Transaction value: $189,728
Shares: -5,316
Change %: -0.77%
Price: $35.69
Shares after: 686,584
Date: 21 Oct 2025
Ownership: By Atlas Venture Opportunity Fund II, L.P.
Footnotes: F4, F5, F8

SION transaction

Common Stock

Sale

Transaction value: $3,023
Shares: -83
Change %: -0%
Price: $36.42
Shares after: 2,309,035
Date: 21 Oct 2025
Ownership: By Atlas Venture Fund XI, L.P.
Footnotes: F1, F3

SION transaction

Common Stock

Sale

Transaction value: $619
Shares: -17
Change %: -0%
Price: $36.42
Shares after: 686,567
Date: 21 Oct 2025
Ownership: By Atlas Venture Opportunity Fund II, L.P.
Footnotes: F4, F5

^* marks a reported price that did not pass the local price check.

Additional SEC filing notes

Filing notes and footnotes

Rule 10b5-1 trading plan

These transactions were reported as open-market trades under a Rule 10b5-1 plan. The plan lets an insider set trading instructions in advance, which can reduce the risk of trading while in possession of material nonpublic information.

Original filing language: transaction made pursuant to a contract, instruction, or written plan intended to satisfy Rule 10b5-1(c).

Explanation of responses 8 footnotes

Footnote 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.

Footnote 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).

Footnote 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.

Footnote 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.

Footnote 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.

Footnote 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.

Footnote 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.

Footnote 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.