Company: SION
Filing Date: 2025-01-24
Form Type: CORRESP
Source: 0001193125-25-012256
Chunk: 10

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-24
Form: CORRESP
Chunk 10
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 2025 Stock Option and Incentive Plan and the applicable stock option agreements thereunder, which will become effective upon the date immediately preceding the date on which the Registration Statement is declared effective by the Commission. Comparison of Most Recent Valuation and the Preliminary Price Range As is typical in IPOs, the Preliminary Price Range was not derived using a formal quantitative determination of fair value but was determined based on discussions among the Company and the underwriters. Prior to January 21, 2025, the Company and the underwriters have not had any specific discussions regarding the Preliminary Price Range. Among the factors that were considered in setting the Preliminary Price Range were the following:

| • |     | the general conditions of the securities market and the recent market prices of, and the demand for, publicly 
 traded common stock of comparable companies;                                                                  |

| • |     | the Company’s financial condition and prospects; |

| • |     | estimates of business potential and earnings prospects for the Company and the industry in which it operates; |

| • |     | valuation metrics for and recent performance of initial public offerings of companies in the biotechnology 
 sector; and                                                                                                |

| • |     | progress and stage of development of the Company’s development programs. |

In addition, the Company believes that the difference between the October 29, 2024 fair value determination of $7.07 per share and the Preliminary Price Range of $[ ***] to $[ ***] per share, each of which do not reflect the anticipated Stock Split, is the result of the factors above and the following factors and continued positive developments with respect to the Company’s business that occurred subsequent to October 29, 2024, the date of the Company’s most recent determination of the fair value of its Common Stock:

| • |     | The Preliminary Price Range is based only upon a scenario in which the Company completes the IPO and is not                                                                                                                                  
 probability weighted, in contrast to the Company’s third-party valuation of the Common Stock as of October 29, 2024, which considered the probability weighting for the IPO scenarios of 25% for the near-term scenario and 25% for the base 
 case scenario with the remaining 50% allocated to a trade sale scenario. If the Company had applied a weighting of 50% to each of the IPO scenarios, the fair value of the Company’s Common Stock in the third-party valuation as of         
 October 29, 2024 would have been $10.11 per share.