Company: SION
Filing Date: 2025-01-24
Form Type: CORRESP
Source: 0001193125-25-012256
Chunk: 12

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-24
Form: CORRESP
Chunk 12
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 Preliminary Price Range for the IPO is reasonable. The Company also refers you to the discussion of its general approach of determining fair value of equity awards set forth in the Registration Statement under the heading “ Management’s Discussion and Analysis of Financial Condition and Results of Operations—Critical Accounting Estimates—Stock-Based Compensation Expense—Determination of Fair Value of Common Stock Valuations” for additional background regarding its equity grant valuation methodologies to date. Because of the financially sensitive nature of the estimated price range, the Company requests confidential treatment under 17 C.F.R. § 200.83 of the contents of this letter and has submitted a separate request for confidential treatment in accordance therewith to the Commission’s Office of Freedom and Information Privacy Act Operations. Pursuant to Rule 418 under the Securities Act of 1933, as amended (the “ Securities Act”), the information contained in this letter is being provided to the Commission on a confidential supplemental basis only and is not to be filed with or deemed part of the Registration Statement. The Company respectfully requests that the Staff return the unredacted version of this letter to it pursuant to Rule 418 of the Securities Act once the Staff has completed its review. We have provided a self-addressed stamped envelope for this purpose. Kindly acknowledge receipt of this letter by stamping the enclosed copy of this letter and returning it in the envelope provided. * * * * If you have any questions or comments regarding the foregoing, or if there is any additional information that we may provide to assist the Staff’s review, please contact the undersigned at (617) 570-1329. 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 9

| Sincerely,          |     |                                              |
| GOODWIN PROCTER LLP |     |                                              |
| By:                 |     | /s/ Gabriela Morales-Rivera                  |
|                     |     | Gabriela Morales-Rivera, Goodwin Procter LLP |

| cc: |     | Michael Cloonan, Sionna Therapeutics, Inc.      |
|     |     | Elena Ridloff, Sionna Therapeutics, Inc.        |
|     |     | Jennifer Fitzpatrick, Sionna Therapeutics, Inc. |
|     |     | William D. Collins, Goodwin Procter LLP         |
|     |     | Janet Hsueh