X0508 4 2025-11-06 0002070849 BillionToOne, Inc. BLLN 0002087877 Rai Akshay 2180 SAND HILL ROAD, STE. 100 MENLO PARK CA 94025 true false false false false Common Stock 2025-11-06 4 A false 8333 0 A 8333 D Common Stock 2025-11-07 4 C false 2676 A 11009 D Common Stock 2025-11-07 4 C false 1784414 A 1784414 I See Footnote Common Stock 2025-11-07 4 J false 11009 D 0 D Common Stock 2025-11-07 4 J false 1784414 D 0 I See Footnote Class A Common Stock 2025-11-07 4 J false 11009 A 11009 D Class A Common Stock 2025-11-07 4 J false 1784414 A 1784414 I See Footnote Series D Convertible Preferred Stock 2025-11-07 4 C false 2676 D Common Stock 2676 0 D Series D Convertible Preferred Stock 2025-11-07 4 C false 1784414 D Common Stock 1784414 0 I See Footnotes Each restricted stock unit (RSU) represents a contingent right to receive one share of the Issuer's Common Stock. The RSUs shall vest over three years in equal annual installments on the anniversary of November 6, 2025, subject to the Reporting Person's continuous service to the Issuer through each such vesting date. The total represents shares received upon conversion of shares of Series D Convertible Preferred Stock. The reported security converted into the Issuer's Common Stock on a one-for-one basis automatically immediately prior to the closing of the Issuer's initial public offering of Class A common stock (the "Offering") without payment of further consideration. The shares have no expiration date. The reported securities are directly held by Wipro Enterprises Private Limited (Wipro), of which Mr. Rai is the nominee/investor director appointed by Wipro Enterprises Limited. Mr. Rai will not have voting or dispositive control of these securities while such securities are held by Wipro and thus disclaims beneficial ownership of such securities. Pursuant to a reclassification exempt under Rule 16b-7, each share of Common Stock was automatically reclassified into one share of Class A common stock immediately prior to the completion of the Offering. /s/ Thomas P. Lynch, Attorney-in-Fact 2025-11-10