Company: SION
Filing Date: 2025-02-03
Form Type: S-1/A
Source: 0001193125-25-018825
Chunk: 124

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-03
Form: S-1/A
Chunk 124
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 offering and investors will be relying on the judgment of our management
regarding the application of the net proceeds. Pending our use of the net proceeds from this offering, we intend to invest the net proceeds in a variety of capital preservation instruments, including short-term and long-term interest-bearing
instruments, investment-grade securities, and direct or guaranteed obligations of the U.S. government. We cannot predict whether the proceeds invested will yield a favorable return.

87

DIVIDEND POLICY

We have never declared or paid cash dividends on our capital stock. We do not anticipate declaring or paying, in the foreseeable future, any cash
dividends on our capital stock. We intend 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.

88

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 27,149,206 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 8,823,529 shares of common stock in this offering at the assumed initial public offering price of $17.00 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