Company: BLLN
Filing Date: 2025-10-07
Form Type: S-1
Source: 0001193125-25-233697
Chunk: 272

Company: BillionToOne, Inc.
Filing Date: 2025-10-07
Form: S-1
Chunk 272
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 equal monthly installments beginning with October 1, 2023, subject to the named executive officer’s continued service to the Company through the applicable vesting 
 date.                                                                                                                                                                                                          |

| (4) |     | Option vests and becomes exercisable in 48 equal monthly installments beginning with September 1, 2021, subject to the named executive officer’s continued service to the Company through the applicable vesting 
 date.                                                                                                                                                                                                            |

Severance and change in control benefits Our Board of Directors has approved the BillionToOne, Inc. Executive Severance Plan (the Severance Plan) prior to this offering to offer severance benefits to our named executive officers and to certain other key executives and employees (each, a Participant). The compensation committee of the Board has the authority to designate the executives and key employees who will be offered an opportunity to participate in the Severance Plan and will administer the Severance Plan. To participate in the Severance Plan, the Participant must enter into a Participation Agreement (each a, Participation Agreement), which provides that the terms and conditions of the Severance Plan shall supersede and replace any existing employment or severance agreement between us and the Participant. Each of Dr. Atay, Mr. Taylor and Ms. Johnson will be eligible to participate in our Severance Plan pursuant to which Dr. Atay will be a Tier 1 Participant, and each of Mr. Taylor and Ms. Johnson will be Tier 2 Participants. Tier 1, Tier 2, and Tier 3 Participants are entitled to the following severance benefits, as applicable: Termination that Does Not Qualify as a Change in Control Termination.In the event of an Involuntary Termination (or, in the case of a Tier 3 Participant, a Termination Without Cause) that is not a Change in Control 205

Termination, a Participant will be eligible to receive the following benefits, provided the Participant signs a release of claims:

| • |     | Continuation of the Participant’s base salary for a period of (i) in the case of Tier 1 Participants, 12 months, (ii) 
 in the case of Tier 2 Participants, 9 months, or, (iii) in the case of a Tier 3 Participant, 6 months.                |

| • |     | Continuation of the Participant’s health and welfare benefits for the shorter of (i) in the case of Tier 1                                                                                                                                         
 Participants, 12 months, in the case of Tier 2 Participants,