Company: SION
Filing Date: 2025-01-24
Form Type: CORRESP
Source: 0001193125-25-012256
Chunk: 6

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-24
Form: CORRESP
Chunk 6
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 date.

February 13, 2024 Valuation

The fair value of the Common Stock of $4.18 per share at February 13, 2024 was determined with the assistance of an independent third-party valuation firm
and approved by the Board on March 13, 2024. This valuation was used to support the fair market value of the Common Stock in accordance with Section 409A of the IRC with respect to options granted on March 13, 2024 and July 15,
2024, along with other factors determined by the Board to be relevant at the time of each such grant of options.

FOIA CONFIDENTIAL TREATMENT REQUESTED BY SIONNA THERAPEUTICS, INC.

Division of Corporation Finance Office of Life Sciences U.S. Securities and Exchange Commission January 24, 2025 Page 5 The February 13, 2024 valuation applied the OPM to allocate the fair value of the Company’s equity to various securities within the Company’s capital structure. Under this method, the OPM was built based on the Company’s capital structure and reasonable option model inputs. The equity value of the Company was determined using a market approach such that the implied value per share of Series C redeemable convertible preferred stock (the “ Series C Preferred Stock”) was equal to its original issue price paid by investors at the closing of the Series C Preferred Stock financing on March 4, 2024. The 30.0% DLOM applied to the fair value of Common Stock was estimated using a put option analysis. The principal factors that contributed to no change in the fair value of the Common Stock from January 25, 2022 to February 13, 2024 include the following:

| • |     | The Company closed its Series C Preferred Stock financing at $9.762 per share. The issuance price of the Series C                              
 Preferred Stock equated to the same price per share as the Series B Preferred Stock with new investors participating in both financing rounds. |

| • |     | The DLOM was reduced from 35.0% to 30.0% during the measurement period. |

Between February 13, 2024 and July 15, 2024, the Company continued to operate its business in the ordinary course and there were no significant developments in its business. On July 11, 2024, the Company entered into a license agreement with AbbVie Global Enterprises Ltd. (“ AbbVie”), in which the Company issued