Shan Riku Sakakibara - 05 Nov 2025 Form 3 Insider Report for BillionToOne, Inc.

Role: Chief Product Officer
Signature: /s/ Thomas P. Lynch, Attorney-in-Fact
Issuer symbol: BLLN on Nasdaq
Transactions as of: 05 Nov 2025
Net transactions value: $0
Form type: 3
Filing time: 05 Nov 2025, 21:38:57 UTC
Next filing: 12 Nov 2025
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
Sakakibara Shan Riku	Chief Product Officer	C/O BILLIONTOONE, INC., 1035 O'BRIEN DRIVE, MENLO PARK	/s/ Thomas P. Lynch, Attorney-in-Fact	05 Nov 2025	0002088547

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
holding	BLLN	Common Stock						220,000	05 Nov 2025	Direct	F1

Derivative Securities (e.g., puts, calls, warrants, options, convertible securities)

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Underlying Class	Amount	Exercise Price	Ownership	Footnotes
holding	BLLN	Stock Option (right to buy)							05 Nov 2025	Common Stock	50,000	$2.80	Direct	F1, F2
holding	BLLN	Stock Option (right to buy)							05 Nov 2025	Common Stock	40,000	$8.65	Direct	F1, F3
holding	BLLN	Stock Option (right to buy)							05 Nov 2025	Common Stock	65,000	$30.78	Direct	F1, F4

* An asterisk sign (*) next to the price indicates that the price is likely invalid.

Explanation of Responses:

Id	Content
F1	Immediately prior to the completion of the Issuer's initial public offering of Class A common stock, each share of Common Stock shall be reclassified into one share of Class A common stock.
F2	The options are fully vested and exercisable.
F3	The options are subject to a service-based vesting requirement, which shall be satisfied over a four-year period. The options vest and become exercisable in equal monthly installments commencing on January 1, 2023, subject to the Reporting Person's continuous service with the Issuer through each such vesting date.
F4	The options are subject to a service-based vesting requirement, which shall be satisfied over a four-year period. The options vest and become exercisable in equal monthly installments commencing on September 15, 2025, subject to the Reporting Person's continuous service with the Issuer through each such vesting date.

Remarks:

Exhibit 24 - Power of Attorney