Company: SION
Filing Date: 2025-01-17
Form Type: S-1
Source: 0001193125-25-008474
Chunk: 272

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 272
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 compensation policy, to be effective as of the date on which the registration statement of which this prospectus forms a part is declared effective by the SEC, and which will supersede all existing board of directors agreements. The policy will be designed to enable us to attract and retain, on a long-term basis, highly qualified non-employeedirectors. Under the policy, our non-employeedirectors will be eligible to receive cash retainers (which will be payable quarterly in arrears and prorated for partial years of service) and equity awards as set forth below:

| Annual Retainer for Board Membership           |     |   |
|:-----------------------------------------------|:----|:--|
| Members                                        |     | $ |
| Additional Retainer for Non-executive Chair    |     | $ |
| Additional Retainer for Committee Membership   |     |   |
| Audit Committee:                               |     |   |
| Members (other than chair)                     |     | $ |
| Chair                                          |     | $ |
| Compensation Committee:                        |     |   |
| Members (other than chair)                     |     | $ |
| Chair                                          |     | $ |
| Nominating and Corporate Governance Committee: |     |   |
| Members (other than chair)                     |     | $ |
| Chair                                          |     | $ |

In addition, the non-employeedirector compensation policy will provide that, upon initial election or appointment to our board of directors, each non-employeedirector will be granted an initial, one-timeequity award consisting of a stock option grant to purchase shares of our common stock (the “Initial Grant”). The Initial Grant will vest in equal annual installments over three years following the grant date, subject to continued service through the applicable vesting date; provided that, notwithstanding the foregoing, each non-employeedirector who was appointed as a member of our board of directors after January 1, 2025 and prior to the effective date of the registration statement of 196

which this prospectus forms a part, shall receive an Initial Grant upon such effective date, with an exercise price equal to the initial offering price per share and that will vest in equal
annual installments over three years following the grant date, subject to continued service through the applicable effective date and vesting dates. Mses. Ruddy and Viney each became a member of our board of directors on January 6, 2025 and will
each receive an Initial Grant upon the effective date of this