Company: SION
Filing Date: 2025-02-03
Form Type: S-1/A
Source: 0001193125-25-018825
Chunk: 303

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-03
Form: S-1/A
Chunk 303
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 NOT TAX ADVICE. PROSPECTIVE INVESTORS SHOULD CONSULT THEIR TAX ADVISORS REGARDING THE PARTICULAR U.S. FEDERAL INCOME TAX CONSEQUENCES TO THEM OF ACQUIRING, OWNING AND DISPOSING OF OUR COMMON STOCK, AS WELL AS ANY TAX CONSEQUENCES ARISING UNDER ANY STATE, LOCAL OR FOREIGN TAX LAWS AND ANY OTHER U.S. FEDERAL TAX LAWS OR UNDER ANY APPLICABLE INCOME TAX TREATY. Definition of Non-U.S.Holder For purposes of this discussion, a non-U.S.holder is any beneficial owner of our common stock that is for U.S. federal income tax purposes:

| • |     | a non-resident alien individual; |

| • |     | a corporation or other organization taxable as a corporation for U.S. federal income taxes that is not created or organized 
 under the laws of the U.S., any state thereof, or the District of Columbia; or                                              |

| • |     | a foreign trust or estate, the income of which is not subject to U.S. federal income tax on a net income basis. |

Distributions on Our Common Stock As described under “ Dividend Policy,” we do not currently anticipate declaring or paying, for the foreseeable future, any cash distributions on our capital stock. However, if we were to distribute cash or other property on our common stock, such distributions will constitute dividends for U.S. federal income tax purposes to the extent paid from our current or accumulated earnings and profits, as determined under U.S. federal income tax principles. Subject to the discussion below regarding effectively connected income, backup withholding and FATCA (as defined below), dividends paid to a non-U.S.holder of our common stock generally will be subject to U.S. federal withholding tax at a rate of 30% of the gross amount of the dividends or such lower rate specified by an applicable income tax treaty. Even if our current or accumulated earnings and profits are less than the amount of the distribution, the applicable withholding agent may elect to treat the entire distribution as a dividend for U.S. federal withholding tax purposes. To receive the benefit of a reduced treaty rate, a non-U.S.holder must furnish us or our withholding agent with a valid IRS Form W-8BEN(in the case of individuals) or IRS Form W-8BEN-E(in the case of entities), or other appropriate form, certifying such holder’s qualification for the reduced rate. This certification must be provided to us or our withholding agent before