Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 247

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 247
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 as other
full-time employees. The 401(k) plan provides eligible employees with an opportunity to save for retirement on a tax advantaged basis. Eligible employees are able to defer eligible compensation subject to applicable annual limits of the Internal
Revenue Code of 1986, as amended (the “Code”). Our 401(k) plan is intended to be qualified under Section 401(a) of the Code with our 401(k) plan’s related trust intended to be tax exempt under Section 501(a) of the Code. As
a tax-qualified retirement plan, contributions to our 401(k) plan and earnings and matching amounts on those contributions are not taxable to the employees until distributed from our 401(k) plan. We did not
provide matching or discretionary contributions under the 401(k) plan during the fiscal year ended December 31, 2024. We believe that providing a vehicle for tax-deferred retirement savings though our
401(k) plan adds to the overall desirability of our executive compensation package and further incentivizes our employees, including our NEOs, in accordance with our compensation policies. Other than the 401(k) plan, we do not provide any qualified
or non-qualified retirement or deferred compensation benefits to our employees, including our NEOs.

Executive Employment Arrangements

We have entered into an offer letter with each of our NEOs in connection with their employment with us, which sets forth the terms
and conditions of each NEO’s employment. Each of Mr. Cloonan, Ms. Ridloff and Dr. McKee has entered into a standard employee confidentiality, assignment and nonsolicitation agreement, pursuant to which each NEO has agreed to
covenants relating to confidentiality and assignment of inventions, as well as covenants not to solicit certain of our service providers and customers during the NEO’s employment and for one year after termination of employment. Dr. McKee has
also agreed to a covenant not to compete during her employment and for one year after termination of employment.

182

Offer Letters in Place for Our NEOs

Michael Cloonan, M.B.A.

In March 2021, we entered into an
offer letter with Mr. Cloonan (the “Cloonan Offer Letter”). Under the Cloonan Offer Letter, Mr. Cloonan is entitled to receive an annual base salary (which has subsequently been increased as described above), an annual bonus
opportunity, and an initial equity grant consisting of 547,343 shares of restricted stock