Company: SION
Filing Date: 2025-02-03
Form Type: S-1/A
Source: 0001193125-25-018825
Chunk: 365

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-03
Form: S-1/A
Chunk 365
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, the Board adopted and approved the 2025 Stock Incentive Plan (the “2025 Plan”), which will become effective upon the date immediately preceding the date on which the registration statement for the proposed IPO is declared effective by the SEC. The 2025 Plan provides for the grant of awards with respect to an additional 5,060,000 shares of common stock. Subject to the effectiveness of the 2025 Plan, the Company will cease the grant of additional awards under the 2020 Plan. F-44

In January 2025, the Board adopted and approved the 2025 Employee Stock Purchase Plan (the
“2025 ESPP”), which will become effective upon the date immediately preceding the date on which the registration statement for the proposed IPO is declared effective by the SEC. The 2025 ESPP initially provides participating employees with
the opportunity to purchase up to an aggregate of 390,127 shares of common stock.

Grant of stock options under the 2025 Plan

In January 2025, the Board approved the grant of options with service-based vesting criteria for the purchase of an aggregate of 1,946,388 shares of common stock, at an
exercise price per share equal to the per share “price to the public” or (equivalent), under the 2025 Plan.

F-45

8,823,529 Shares Common Stock Preliminary Prospectus

| Goldman Sachs & Co. LLC |     | TD Cowen |     | Stifel |     | Guggenheim Securities |

Until , 2025 (25 days after the date of this prospectus), all dealers that effect transactions in these securities, whether or not participating in this offering, may be required to deliver a prospectus. This delivery requirement is in addition to the dealers’ obligation to deliver a prospectus when acting as underwriters and with respect to their unsold allotments or subscriptions. , 2025

PART II INFORMATION NOT REQUIRED IN PROSPECTUS Unless otherwise indicated, all references to “Sionna,” the “company,” “we,” “our,” “us” or similar terms refer to Sionna Therapeutics, Inc. and its wholly owned subsidiary, or either or both of them as the context may require. Item 13. Other Expenses of Issuance and Distribution. The following table sets forth all expenses to be paid by us, other than underwriting discounts and commissions, in connection with this offering. All amounts shown are estimates except for the Securities and Exchange Commission