Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 359

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 359
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 |   (78,400 | ) |     |                  | 6.11 |     |                  |     |     |                 |       |
| Outstanding as of September 30, 2024 |     |           | 3,652,051 |   |     | $                | 5.77 |     |                  | 8.5 |     | $               | 8,439 |
| Exercisable as of September 30, 2024 |     |           | 1,289,683 |   |     | $                | 5.26 |     |                  | 7.6 |     | $               | 3,643 |

Stock-Based Compensation Expense The Company recorded stock-based compensation in the accompanying condensed consolidated statements of operations and comprehensive loss as follows (in thousands):

|                                    |     | Nine Months Ended September 30, |  2024 |     |   |  2023 |
|:-----------------------------------|:----|:--------------------------------|------:|:----|:--|------:|
| Research and development expense   |     | $                               | 1,082 |     | $ |   849 |
| General and administrative expense |     |                                 | 1,562 |     |   |   838 |
| Total                              |     | $                               | 2,644 |     | $ | 1,687 |

As of September 30, 2024, there was $10.4 million of unrecognized stock-based compensation expense for common stock option awards that are expected to be recognized over a weighted average period of 2.9 years. As of September 30, 2024, there was $0.1 million of unrecognized stock-based compensation expense for restricted common stock awards that are expected to be recognized over a weighted average period of 0.6 years. F-43

12. Net Loss Per Share Basic and diluted net loss per share attributable to common stockholders was calculated as follows for the periods presented (in thousands, except share and per share amounts):

| Numerator:                                                                             |     | Nine Months Ended September 30, 
 2024                            |           |   |     | 2023 |           |   |
|:---------------------------------------------------------------------------------------|:----|:--------------------------------|----------:|:--|:----|:-----|----------:|:--|
| Net loss                                                                               |     | $                               |   (45,840 | ) |     | $    |   (35,