Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 318

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 318
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 available for review at the website of the SEC referred to above.

We also maintain a website at www.sionnatx.com. Information contained in, or accessible through, our website is not a part of this prospectus,
and the inclusion of our website address in this prospectus is only as an inactive textual reference. Upon completion of this offering, you may access, free of charge, our annual reports on Form 10-K,
quarterly reports on Form 10-Q, current reports on Form 8-K and amendment to those reported filed or furnished pursuant to Section 13(a) or 15(d) of the Exchange
Act as soon as reasonably practicable after such material is electronically filed with, or furnished to, the SEC.

229

INDEX TO CONSOLIDATED FINANCIAL STATEMENTS Consolidated Financial Statements for the Years Ended December 31, 2023 and 2022:

| Report of Independent Registered Public Accounting Firm                  |     | F-2 |
| Consolidated Balance Sheets                                              |     | F-3 |
| Consolidated Statements of Operations and Comprehensive Loss             |     | F-4 |
| Consolidated Statements of Convertible Preferred Stock and Stockholders’ 
 Deficit                                                                  |     | F-5 |
| Consolidated Statements of Cash Flows                                    |     | F-6 |
| Notes to Consolidated Financial Statements                               |     | F-7 |

Unaudited Interim Condensed Consolidated Financial Statements for the Nine Months Ended September 30, 2024 and 2023:

| Condensed Consolidated Balance Sheets                                              |     | F-30 |
| Condensed Consolidated Statements of Operations and Comprehensive Loss             |     | F-31 |
| Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders’ 
 Deficit                                                                            |     | F-32 |
| Condensed Consolidated Statements of Cash Flows                                    |     | F-34 |
| Notes to Condensed Consolidated Financial Statements                               |     | F-35 |

F-1

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

To the stockholders and the Board of Directors of Sionna Therapeutics, Inc.

Opinion on the Financial Statements

We have audited the accompanying
consolidated balance sheets of Sionna Therapeutics, Inc., and subsidiary (the “Company”) as of December 31, 2023 and 2022, the related consolidated statements of operations and comprehensive loss, convertible preferred stock and
stockholders’ deficit, and cash flows