Company: SION
Filing Date: 2025-02-04
Form Type: 8-A12B
Source: 0001193125-25-020023
Chunk: 0

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-04
Form: 8-A12B
Chunk 0
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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 FORM 8-A FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES PURSUANT TO SECTION 12(b) OR (g) OF THE SECURITIES EXCHANGE ACT OF 1934 Sionna Therapeutics, Inc. (Exact name of registrant as specified in its charter)

| Delaware                                 |     |                          84-2801521 |
| (State of incorporation or organization) |     | -I.R.S. Employer Identification No. |
| 21 Hickory Drive, Suite 500              
 Waltham, MA                              |     |                               02451 |
| (Address of principal executive offices) |     |                           -Zip Code |

Securities to be registered pursuant to Section 12(b) of the Act:

| Title of each class                      
 to be so registered                      |     | Name of each exchange on which 
 each class is to be registered |
| Common Stock, par value $0.001 per share |     | The Nasdaq Stock Market LLC    |

If this form relates to the registration of a class of securities pursuant to Section 12(b) of the Exchange Act and is effective pursuant to General Instruction A.(c) or (e), check the following box. ☒ If this form relates to the registration of a class of securities pursuant to Section 12(g) of the Exchange Act and is effective pursuant to General Instruction A.(d) or (e), check the following box. ☐ If this form relates to the registration of a class of securities concurrently with a Regulation A offering, check the following box. ☐ Securities Act registration statement file or Regulation A offering statement number to which this form relates (if applicable): 333-284352 Securities to be registered pursuant to Section 12(g) of the Act: None

INFORMATION REQUIRED IN REGISTRATION STATEMENT

| Item 1. | Description of Registrant’s Securities to be Registered. |

For a description of Sionna Therapeutics, Inc.’s (the “Registrant”) common stock, par value $0.001 per share (the “Common Stock”), to be registered hereunder, reference is made to the information set forth under the heading “Description of Capital Stock” in the Registrant’s prospectus that constitutes a part of the Registrant’s Registration Statement on Form S-1,as amended (File No. 333-284352)(the “Registration Statement”), filed with the Securities