Oguzhan Atay - 05 Nov 2025 Form 3 Insider Report for BillionToOne, Inc.

Role: Chairman and Chief Executive Officer Exhibit 24 - Power of Attorney, Director
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, 21:32:08 UTC
Next filing: 12 Nov 2025
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
Atay Oguzhan	Chairman and Chief Executive Officer Exhibit 24 - Power of Attorney, Director	C/O BILLIONTOONE, INC., 1035 O'BRIEN DRIVE, MENLO PARK	/s/ Thomas P. Lynch, Attorney-in-Fact	05 Nov 2025	0002088549

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
holding	BLLN	Common Stock						1,965,108	05 Nov 2025	Direct	F1
holding	BLLN	Common Stock						200,000	05 Nov 2025	By spouse	F2, F3

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	Series A-1 Convertible Preferred Stock							05 Nov 2025	Common Stock	262,434		Direct	F4
holding	BLLN	Stock Option (right to buy)							05 Nov 2025	Common Stock	640,000	$2.80	Direct	F2, F5
holding	BLLN	Stock Option (right to buy)							05 Nov 2025	Common Stock	1,003,102	$20.04	Direct	F2, F6

* 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 (the "Offering"), each share of Common Stock shall be reclassified into one share of Class A common stock and such shares of Class A common stock shall be exchanged at a 1:1 ratio for shares of Class B common stock.
F2	Immediately prior to the completion of the Offering, each share of Common Stock shall be reclassified into one share of Class A common stock.
F3	Represents shares held directly by the Reporting Person's spouse.
F4	The reported security is convertible into the Issuer's Common Stock on a one-for-one basis at any time at the holder's election and shall automatically convert into Class A common stock immediately prior to the completion of the Offering without payment of further consideration. The shares have no expiration date. Immediately prior to the completion of the Offering, such shares of Class A common stock shall be exchanged at a 1:1 ratio for shares of Class B common stock.
F5	The options are fully vested and exercisable.
F6	The options are subject to a service-based vesting requirement, which shall be satisfied over a six-year period. The options vest and become exercisable in equal monthly installments commencing on June 11, 2025, subject to the Reporting Person's continuous service with the Issuer through each such vesting date.

Remarks:

Chairman and Chief Executive Officer Exhibit 24 - Power of Attorney