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

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 17
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.001 per share (the “Series C preferred stock” and, together with the Series Seed preferred stock, Series A preferred stock and Series B preferred stock, the “preferred stock”) into an aggregate of 39,667,715 shares of our common stock immediately prior to the completion of this offering, and excludes:

| • |     | 5,336,077 shares of common stock issuable upon exercise of outstanding stock options as of September 30, 2024 under        
 our 2020 Stock Option and Grant Plan, as amended (“2020 Plan”), with a weighted average exercise price of $3.95 per share; |

| • |     | 93,141 shares of common stock issuable upon exercise of outstanding stock options granted after September 30, 2024 
 pursuant to our 2020 Plan, with a weighted average exercise price of $7.07 per share;                              |

| • |     | 1,606,629 shares of common stock reserved for future issuance as of September 30, 2024 under the 2020 Plan, which will        
 cease to be available for issuance at the time that our 2025 Stock Option and Incentive Plan (“2025 Plan”) becomes effective; |

| • |     | shares of common stock reserved for future issuance under our 2025 Employee Stock Purchase                                                                                                                                                    
 Plan (“ESPP”), which will become effective on the date immediately prior to the effectiveness of the registration statement of which this prospectus forms a part, as well as any automatic increases in the number of shares of common stock 
 reserved for future issuance under the ESPP; and                                                                                                                                                                                              |

| • |     | shares of our common stock that will become available for future issuance under our 2025 Plan,                                                                                                                                                     
 which will become effective on the date immediately prior to the effectiveness of the registration statement of which this prospectus forms a part, as well as any automatic increases in the number of shares of common stock reserved for future 
 issuance under the 2025 Plan and any shares underlying outstanding stock awards granted under the 2020 Plan that expire or are repurchased, forfeited, cancelled or withheld.                                                                      |

Unless otherwise indicated, the information in this prospectus reflects or assumes the following:

| • |     | a 1-for-    reverse                                                                                    
 stock split of our common stock, which will become effective prior to the completion of this offering; |

| • |     | the automatic conversion of all outstanding shares of our preferred