Company: SION
Filing Date: 2025-02-07
Form Type: 424B4
Source: 0001193125-25-022709
Chunk: 256

Company: Sionna Therapeutics, Inc.
Filing Date: 2025-02-07
Form: 424B4
Chunk 256
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 75% of the shares vest in 36 equal monthly installments thereafter, in each case, subject to the NEO’s continuous “service relationship” (as defined in the 2020   
 Plan) with us through each applicable vesting date. Notwithstanding the foregoing, this award is subject to acceleration of vesting benefits as set forth in the NEO’s Severance and CIC Agreement and/or the New Severance and CIC Plan, as 
 applicable.                                                                                                                                                                                                                                  |

| (4) | The shares underlying this stock option award vest in 48 equal monthly installments over a four-year period following the                                                                                                                           
 vesting commencement date, in each case, subject to the NEO’s continuous “service relationship” (as defined in the 2020 Plan) with us through each applicable vesting date. Under the applicable award agreement, the shares underlying             
 this option will become fully vested upon a sale event (as defined in the 2020 Plan), which does not include this offering. Notwithstanding the foregoing, this award is also subject to acceleration of vesting benefits as set forth in the NEO’s 
 Severance and CIC Agreement and/or the New Severance and CIC Plan, as applicable.                                                                                                                                                                   |

| (5) | The shares underlying this award vest over a four-year period as follows: 25% of such shares vested on the first                                                                                                                       
 anniversary of the vesting commencement date, and the remaining 75% of the shares vest in 36 equal monthly installments thereafter, in each case, subject to the NEO’s continuous “service relationship” (as defined in the 2020 Plan) 
 with us through each applicable vesting date. Under the applicable award agreement, the shares underlying this award will become fully vested                                                                                          |

187

| upon a sale event (as defined in the 2020 Plan) of our company, which does not include this offering. Notwithstanding the foregoing, this award is also subject to acceleration of vesting benefits                              
 as set forth in the NEO’s offer letter, the NEO’s Severance and CIC Agreement and/or the New Severance and CIC Plan, as applicable. For Dr. McKee’s restricted stock award only, such award is also subject to certain tag along 
 rights upon a sale event.                                                                                                                                                                                                        |

Employee Benefit and Equity Compensation Plans 2020 Stock Option and Grant Plan Our 2020 Plan was initially adopted by our board of directors, and approved by our stockholders, on August 20, 2020 and