144 0002088549 XXXXXXXX LIVE 0002070849 BillionToOne, Inc. 001-42934 1035 O'BRIEN DRIVE MENLO PARK CA 8593860965 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 1525645.67 41442834 07/06/2026 NASDAQ Class A 05/01/2024 Pre-IPO Shares Issuer N 12500 05/01/2024 Cash N Ezgi N. Akcinar Atay

1035 O'Brien Drive Menlo Park CA 94025

Class A 06/08/2026 12500 1227812.50 Oguzhan Atay

1035 O'Brien Drive Menlo Park CA 94025

Class A 06/08/2026 26250 2563632.00 Atay 2021 Dynasty Trust

1035 O'Brien Drive Menlo Park CA 94025

Class A 06/08/2026 2500 245562.50 Today's sale and sales within the past 3 months occurred in the account of Ezgi N. Akcinar Atay, who is the spouse of Oguzhan Atay, an Officer and Director of the company. There are also sales within the past 3 months which occurred in the Atay 2021 Dynasty Trust which were made by Icontrust Llc, trustee on the account. Oguzhan Atay is an account stakeholder in the Atay 2021 Dynasty Trust. 07/06/2026 03/07/2026 /s/ Joshua Schmitt, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for Oguzhan Atay.