Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 273

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 273
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,000 |
| Chair                                          |     | $ | 12,000 |
| Nominating and Corporate Governance Committee: |     |   |        |
| Members (other than chair)                     |     | $ |  4,500 |
| Chair                                          |     | $ |  9,000 |

In addition, the non-employeedirector compensation policy provides that, upon initial election or appointment to our board of directors after the effective date of the registration statement of which this prospectus forms a part, each non-employeedirector will be granted an initial, one-timeequity award consisting of a stock option grant to purchase 39,919 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. Mses. Ruddy and Viney each became a member of our board of directors on January 6, 2025 and each received an Initial Grant upon the 197

effective date of this registration statement, with terms in accordance with the non-employee director compensation policy described above. Furthermore, on the date of each annual meeting of
stockholders following the completion of this offering, each non-employee director who continues as a non-employee director following such meeting (other than a director
receiving an Initial Grant on the date of such meeting) will be granted an annual stock option award to purchase 19,959 shares of our common stock (the “Annual Grant”). The Annual Grant will vest in full upon the earlier of (i) the
first anniversary of the date of grant or (ii) the date of the next annual meeting of stockholders, subject to continued service through the applicable vesting date. Following the effective date of the
non-employee director compensation policy, if a non-employee director joins our board of directors on a date other than the date of the annual meeting of stockholders,
then in lieu of a full Annual Grant, such non-employee director will be granted a pro-rated portion of the Annual Grant based on the number of full months between the
director’s initial election or appointment and such annual meeting of stockholders, which will vest in accordance with the same terms as the Annual Grants. The Initial Grants and Annual Grants (including any pro rata portions thereof) will each
expire ten years from the applicable date of grant and have an exercise price per share equal to the fair market value of our common stock on the date of