Nancy JoAnn Johnson - 07 Nov 2025 Form 4 Insider Report for BillionToOne, Inc.

Role: Senior Vice President of Sales and Commercial Operations
Signature: /s/ Thomas P. Lynch, Attorney-in-Fact
Issuer symbol: BLLN on Nasdaq
Transactions as of: 07 Nov 2025
Net transactions value: +$414,000
Form type: 4
Filing time: 12 Nov 2025, 18:07:34 UTC
Previous filing: 05 Nov 2025
SEC: View on sec.gov

Reporting Owners (1)

Name	Relationship	Address	Signature	Signature date	CIK
Johnson Nancy JoAnn	Senior Vice President of Sales and Commercial Operations	C/O BILLIONTOONE, INC., 1035 O'BRIEN DRIVE, MENLO PARK	/s/ Thomas P. Lynch, Attorney-in-Fact	12 Nov 2025	0002087387

Transactions Table

Type	Sym	Class	Transaction	Value $	Shares	Change %	* Price $	Shares After	Date	Ownership	Footnotes
transaction	BLLN	Common Stock	Other		-29,000	-100%		0	07 Nov 2025	Direct	F1
transaction	BLLN	Class A Common Stock	Other		+29,000			29,000	07 Nov 2025	Direct	F1
transaction	BLLN	Class A Common Stock	Purchase	$414,000	+6,900	+24%	$60.00^*	35,900	07 Nov 2025	Direct	F2

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
transaction	BLLN	Stock Option (right to buy)	Other		-125,000	-100%		0	07 Nov 2025	Common Stock	125,000	$0.4500	Direct	F1, F3
transaction	BLLN	Stock Option (right to buy)	Other		+125,000			125,000	07 Nov 2025	Class A Common Stock	125,000	$0.4500	Direct	F1, F3
transaction	BLLN	Stock Option (right to buy)	Other		-25,000	-100%		0	07 Nov 2025	Common Stock	25,000	$2.80	Direct	F1, F3
transaction	BLLN	Stock Option (right to buy)	Other		+25,000			25,000	07 Nov 2025	Class A Common Stock	25,000	$2.80	Direct	F1, F3
transaction	BLLN	Stock Option (right to buy)	Other		-25,000	-100%		0	07 Nov 2025	Common Stock	25,000	$2.80	Direct	F1, F3
transaction	BLLN	Stock Option (right to buy)	Other		+25,000			25,000	07 Nov 2025	Class A Common Stock	25,000	$2.80	Direct	F1, F3
transaction	BLLN	Stock Option (right to buy)	Other		-40,000	-100%		0	07 Nov 2025	Common Stock	40,000	$11.55	Direct	F1, F4
transaction	BLLN	Stock Option (right to buy)	Other		+40,000			40,000	07 Nov 2025	Class A Common Stock	40,000	$11.55	Direct	F1, F4
transaction	BLLN	Stock Option (right to buy)	Other		-20,000	-100%		0	07 Nov 2025	Common Stock	20,000	$17.12	Direct	F1, F5
transaction	BLLN	Stock Option (right to buy)	Other		+20,000			20,000	07 Nov 2025	Class A Common Stock	20,000	$17.12	Direct	F1, F5
transaction	BLLN	Stock Option (right to buy)	Other		-40,000	-100%		0	07 Nov 2025	Common Stock	40,000	$30.78	Direct	F1, F6
transaction	BLLN	Stock Option (right to buy)	Other		+40,000			40,000	07 Nov 2025	Class A Common Stock	40,000	$30.78	Direct	F1, F6

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

Explanation of Responses:

Id	Content
F1	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 Issuer's initial public offering of Class A common stock (the "Offering").
F2	These shares of Class A common stock were purchased by the Reporting Person through a directed share program in connection with the Offering.
F3	The options are fully vested and exercisable.
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 October 1, 2023, subject to the Reporting Person's continuous service with the Issuer through each such vesting date.
F5	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 October 6, 2024, subject to the Reporting Person's continuous service with the Issuer through each such vesting date.
F6	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:

Senior Vice President of Sales and Commercial Operations