Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 296

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 296
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 or exchangeable for common stock for a period of not less than 180 days from the date of this prospectus without the prior written consent of Goldman Sachs & Co. LLC
and TD Securities (USA) LLC, subject to certain exceptions. See the section titled “Underwriting” appearing elsewhere in this prospectus for more information.

Registration Rights

Upon completion of this offering,
certain holders of our securities will be entitled to various rights with respect to registration of their shares under the Securities Act. Registration of these shares under the Securities Act would result in these shares becoming fully tradable
without restriction under the Securities Act immediately upon the effectiveness of the registration. See the section titled “Description of Capital Stock—Registration Rights” appearing elsewhere in this prospectus for more
information.

214

MATERIAL U.S. FEDERAL INCOME AND ESTATE TAX CONSEQUENCES FOR NON-U.S.HOLDERS The following is a summary of material U.S. federal income and estate tax consequences to non-U.S.holders (as defined below) of the purchase, ownership and disposition of our common stock issued pursuant to this offering. This discussion is based on the Internal Revenue Code of 1986, as amended (referred to as the “Code”), Treasury Regulations promulgated thereunder, judicial decisions, and published rulings and administrative pronouncements of the IRS all as in effect on the date hereof. These authorities are subject to differing interpretations and may change, possibly retroactively, resulting in U.S. federal income or estate tax consequences different from those discussed below. We have not requested a ruling from the IRS with respect to the statements made and the conclusions reached in the following summary, and there can be no assurance that the IRS or a court will agree with such statements and conclusions. This discussion is limited to non-U.S.holders who purchase our common stock pursuant to this offering and who hold our common stock as a “capital asset” within the meaning of Section 1221 of the Code (generally, property held for investment). This discussion is not a complete analysis of all potential U.S. federal income or estate tax consequences relating thereto, does not address the potential application of the Medicare contribution tax on net investment income, the alternative minimum tax, or the special tax accounting rules under Section 451(b) of the Code, and also does not address any U.S. federal non-incometax consequences, such as estate or gift tax consequences, or any tax consequences arising under any state, local or foreign tax laws. This discussion does