Company: SION
Filing Date: 2025-01-17
Form Type: S-1
Source: 0001193125-25-008474
Chunk: 351

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-01-17
Form: S-1
Chunk 351
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losures.

In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740: Improvements to Income Tax Disclosures)(“ASU 2023-09”). ASU 2023-09 provides more transparency about income tax information through improvements to income tax disclosures
primarily related to the rate reconciliation

F-36

and incomes taxes paid information. For public companies, the amendments are effective for annual periods beginning after December 15, 2024 and should be applied prospectively. The Company has determined that the effects of adopting the amendments in ASU 2023-09will not have a material impact on its condensed consolidated financial position, the results of its operations, or related disclosures when such amendment is adopted. In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40): Disaggregation of Income Statement Expenses (“ASU 2024-03”),which requires entities to disclose additional information about specific expense categories in the notes to the financial statements. ASU 2024-03 is effective for annual periods beginning after December 15, 2026 and for interim periods within fiscal years beginning after December 15, 2027. Early adoption is permitted. ASU 2024-03 may be applied retrospectively or prospectively. The Company is currently evaluating the effect of this update on its consolidated financial statements and related disclosures. 3. Marketable Securities The following table summarizes the amortized cost and estimated fair value of the Company’s current and noncurrent marketable securities, which are considered to be available-for-saleinvestments and were included in marketable securities (in thousands):

|                                         |     | September 30, 2024 |         |     |            |     |     |            |   |     |            |         |
|:----------------------------------------|:----|:-------------------|--------:|:----|:-----------|----:|:----|:-----------|:--|:----|:-----------|--------:|
|                                         |     | Amortized          
 Cost               |         |     | Unrealized 
 Gains      |     |     | Unrealized 
 Losses     |   |     | Fair Value |         |
| Marketable securities, current:         |     |                    |         |     |            |     |     |            |   |     |            |         |
|