Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 263

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 263
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 in recognition of past services or for other valid consideration and may be issued in lieu
of cash compensation due to such participant.

Our administrator may grant dividend equivalent rights to participants that entitle the recipient to
receive credits for dividends that would be paid if the recipient had held a specified number of shares of common stock.

Our administrator may
grant cash-based awards under the 2025 Plan to participants, subject to the achievement of certain performance goals, including continued employment (or other Service Relationship (as defined in the 2025 Plan)).

The 2025 Plan provides that in the case of and subject to the consummation of a “sale event,” as defined in the 2025 Plan, an acquirer or
successor entity may assume, continue or substitute outstanding awards under the 2025 Plan. To the extent that awards granted under the 2025 Plan are not assumed or continued or substituted by the successor entity, upon the effective time of the
sale event, such awards shall terminate. In such case, except as may be otherwise provided in the relevant award agreement, all awards with time-based vesting conditions or restrictions shall become fully vested and nonforfeitable as of the
effective time of the sale event and all awards with conditions and restrictions relating to the attainment of performance goals may become vested and nonforfeitable in connection with a sale event in the administrator’s discretion or to the
extent specified in the relevant award agreement. In the event of such termination, (i) individuals holding options and stock appreciation rights will be permitted to exercise such options and stock appreciation rights (to the extent then
exercisable (after taking into account any acceleration thereunder)) within a specified period of time prior to the sale event or (ii) we may make or provide for a payment, in cash or in kind, to participants holding vested and exercisable
options and stock appreciation rights equal to the difference between the per share consideration payable to stockholders in the sale event and the

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exercise price of the options or stock appreciation rights and we may make or provide for a payment, in cash or in kind, to participants holding other vested awards in an amount equal to the per
share consideration payable to stockholders in the sale event multiplied by the number of vested shares under such award.

Our board of directors
may amend or discontinue the 2025 Plan and our administrator may amend or cancel outstanding awards for purposes of satisfying changes in law or any other lawful purpose, but no such action may materially and adversely affect rights