Company: SION
Filing Date: 2025-01-17
Form Type: S-1
Source: 0001193125-25-008474
Chunk: 264

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 264
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share consideration payable to stockholders in the sale event multiplied by the number of vested shares under such award.

Our board of directors
may amend or discontinue the 2025 Plan and our administrator may amend or cancel outstanding awards for purposes of satisfying changes in law or any other lawful purpose, but no such action may materially and adversely affect rights under an award
without the holder’s consent. Certain amendments to the 2025 Plan require the approval of our stockholders. The administrator of the 2025 Plan is specifically authorized to exercise its discretion to reduce the exercise price of outstanding
stock options and stock appreciation rights or effect the repricing of such awards through cancellation and re-grants or cancellation in exchange for cash or other awards, in each case, without stockholder
approval. No awards may be granted under the 2025 Plan after the date that is 10 years from the effective date of the 2025 Plan. No awards under the 2025 Plan have been made prior to the date of this prospectus.

2025 Employee Stock Purchase Plan

Our 2025 Employee
Stock Purchase Plan (the “ESPP”) was approved by our board of directors on , adopted by our stockholders on , and will become effective on the date immediately preceding the date on which the
registration statement of which this prospectus forms a part is declared effective by the SEC. The ESPP has two components: a component intended to qualify as an “employee stock purchase plan” within the meaning of Section 423 of the
Code (the “423 Component”), and a component that is not intended to qualify (the “Non-423 Component”). Except as otherwise provided, the Non-423
Component will be operated and administered in the same manner as the 423 Component, except where prohibited by law or as provided by the administrator. The following summary describes the material terms of the ESPP. This summary is not a complete
description of all provisions of the ESPP and is qualified in its entirety by reference to the ESPP, which will be filed as an exhibit to the registration statement of which this prospectus forms a part.

The ESPP initially reserves and authorizes the issuance of up to a total of shares of our common stock to participating employees. The
ESPP provides that the number of shares reserved and available for issuance will automatically be cumulatively increased on January 1, 2026 and each January 1 thereafter through January 1, 2034, by the least of
(i) shares of common stock,