Company: SION
Filing Date: 2025-01-17
Form Type: S-1
Source: 0001193125-25-008474
Chunk: 356

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 356
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 the Company or a Deemed Liquidation Event, the conversion right shall terminate at the close of business on the last full day preceding the date fixed for the payment of any such amounts distributable on such event to the holders of Preferred Stock. All shares of Preferred Stock will automatically convert into shares of common stock upon a qualified initial public offering, which based on the conversion prices currently in effect, would result in a conversion on a one-to-onebasis. 10. Common Stock The voting, dividend and liquidation rights of the holders of the Company’s common stock are subject to and qualified by the rights, powers and preference of the holders of the Preferred Stock set forth in Note 10, “ Convertible Preferred Stock” in the audited consolidated annual financial statements for the years ended December 31, 2023 and 2022 included elsewhere in this prospectus. The number of shares of common stock that have been reserved for future issuances is as follows:

|                                               |     | September 30, |            |     | December 31, |            |
|                                               |     |          2024 |            |     |         2023 |            |
| Convertible Preferred Stock                   |     |               | 39,667,715 |     |              | 21,038,745 |
| Options to purchase common stock              |     |               |  5,336,077 |     |              |  2,797,110 |
| Remaining shares reserved for future issuance |     |               |  1,606,629 |     |              |  1,132,950 |
| Unvested restricted common stock              |     |               |    174,807 |     |              |    383,031 |
| Total                                         |     |               | 46,785,228 |     |              | 25,351,836 |

11. Stock-Based Compensation 2020 Stock Option and Grant Plan The Company’s 2020 Stock Option and Grant Plan was amended by the Board of Directors of the Company (the “Board”) during the nine months ended September 30, 2024 and provided for the issuance of 55,200,000 shares of common stock as of September 30, 2024. F-42

Restricted Common Stock A summary of the Company’s restricted common stock activity during the nine months ended September 30, 2024 is presented below:

|                                   |     | Number of  
 Restricted 
 Common     
 Stock      
 Awards     |          |