144 0002088549 XXXXXXXX LIVE 0002070849 BillionToOne, Inc. 001-42934 1035 O'BRIEN DRIVE MENLO PARK CA 94025 650-460-2551 Atay Oguzhan Member of immediate family of any of the foregoing Class A Fidelity Brokerage Services LLC

900 Salem Street Smithfield RI 02917

12500 1227812.50 41442834 06/08/2026 NASDAQ Class A 05/01/2024 Pre-IPO Shares Issuer N 12500 05/01/2024 Cash Y Today's sale occurred in the account of Ezgi N. Akcinar Atay, who is the spouse of Oguzhan Atay, an Officer and Director of the company. 06/08/2026 03/07/2026 /s/ Gerardo Ibarra-Munoz, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Oguzhan Atay