Company: SION
Filing Date: 2025-01-17
Form Type: S-1
Source: 0001193125-25-008474
Chunk: 122

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 122
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 to retain all available funds and future earnings, if any, to fund the development and expansion of our business, and we do not anticipate paying any cash dividends in the foreseeable future. Any future
determination regarding the declaration and payment of dividends, if any, will be at the discretion of our board of directors, subject to applicable laws, and will depend on then-existing conditions, including our financial condition, operating
results, contractual restrictions, capital requirements, business prospects and other factors our board of directors may deem relevant.

In
addition, our ability to pay cash dividends on our capital stock in the future may be limited by the terms of any future debt or preferred securities we issue or any credit facilities we enter into.

87

CAPITALIZATION The following table sets forth our cash, cash equivalents and investments in marketable securities and total capitalization as of September 30, 2024:

| • |     | on an actual basis; |

| • |     | on a pro forma basis, giving effect to (i) the automatic conversion of all outstanding shares of preferred stock into                                                                                                                              
 an aggregate of 39,667,715 shares of common stock immediately prior to the completion of this offering and (ii) the filing and effectiveness of our fifth amended and restated certificate of incorporation, which will occur immediately prior to 
 the completion of this offering; and                                                                                                                                                                                                               |

| • |     | on a pro forma as adjusted basis, giving effect to (i) the pro forma adjustments set forth above and (ii) the                                                                                                     
 issuance and sale of    shares of common stock in this offering at the assumed initial public offering price of $  per share, the midpoint of the estimated offering price range listed on the cover page of this 
 prospectus, after deducting estimated underwriting discounts and commissions and estimated offering expenses payable by us.                                                                                       |

The pro forma as adjusted information below is illustrative only, and our capitalization following the completion of this offering will be adjusted based on the actual initial public offering price and other terms of this offering determined at pricing. You should read this information in conjunction with our audited consolidated financial statements and the related notes included elsewhere in this prospectus and in “ Management’s Discussion and Analysis of Financial Condition and Results of Operations.”

|                                                                                                                                                                         |     | As of September 30, 2024 |          |   |     |           |          |   |     |                |   |
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