BillionToOne counsel exercises options on 2,000 shares

After the exercise, the officer directly held 10,700 Class A common shares, with a reported stock-option position of 38,974 shares.

Rhea-AI Filing Summary

BillionToOne, Inc. (BLLN) General Counsel, Chief Compliance Officer and Secretary Thomas P. Lynch exercised options covering 2,000 shares of Class A common stock on October 13, 2026, at an exercise price of $8.65 per share. Afterward, he directly held 10,700 shares of Class A common stock; his reported stock-option position was 38,974 shares. The options were fully vested and exercisable.

Insider Trade Summary

2,000 shares exercised/converted

Exercise 2 txns

Insider Lynch Thomas P.

Role See Remarks

Type	Security	Shares	Price	Value
Exercise	Stock Option (right to buy) F1	2,000	$8.65	$17K
Exercise	Class A Common Stock	2,000	$8.65	$17K

Holdings After Transaction: Stock Option (right to buy) — 38,974 contracts (Direct); Class A Common Stock — 10,700 shares (Direct)

Footnotes (1)

1. F1. The options are fully vested and exercisable. The terms of the underlying option grant are as previously reported on the Reporting Person's Form 3 filed on November 5, 2025.

Key Figures

Shares covered by options exercised: 2,000 shares Exercise price: $8.65 per share Class A common shares held after exercise: 10,700 shares +1 more

4 metrics

Shares covered by options exercised 2,000 shares October 13, 2026

Exercise price $8.65 per share Options exercised October 13, 2026

Class A common shares held after exercise 10,700 shares Direct holdings following the October 13, 2026 transaction

Shares in reported stock-option position 38,974 shares Following the October 13, 2026 transaction

Key Terms

Stock Option (right to buy), fully vested and exercisable, Class A Common Stock

3 terms

Stock Option (right to buy) financial

"Stock Option (right to buy)"

fully vested and exercisable technical

"The options are fully vested and exercisable."

Class A Common Stock financial

"underlying_security_title: Class A Common Stock"

Class A common stock is a category of a company’s shares that carries a specific set of ownership rights—most commonly defined voting power and claims on dividends—set out in the company’s charter. For investors it matters because the class determines how much influence you have over corporate decisions, the share’s likely dividend and trading behavior, and how it compares in value to other share classes, like choosing a particular seat with different privileges at the company’s decision-making table.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many BLLN shares did Thomas P. Lynch acquire through options, and at what price?

Thomas P. Lynch exercised options covering 2,000 shares of Class A common stock at an exercise price of $8.65 per share on October 13, 2026.

Were Thomas P. Lynch’s BLLN options vested when he exercised them?

The options were fully vested and exercisable. The underlying option grant’s terms had previously been reported on Thomas P. Lynch’s Form 3 filed November 5, 2025.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Available on EDGAR 10/19/2026 - 07:35 PM EDT Accepted by SEC EDGAR 10/19/2026 - 07:35 PM EDT Learn about SEC filing dates

SEC Form 4

FORM 4

UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Lynch Thomas P.

(Last) (First) (Middle)

C/O BILLIONTOONE, INC.

1035 O'BRIEN DRIVE

(Street)

MENLO PARK CALIFORNIA 94025

(City) (State) (Zip)

UNITED STATES

(Country)

2. Issuer Name and Ticker or Trading Symbol
BillionToOne, Inc. [ BLLN ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	See Remarks

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
10/13/2026

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

4. If Amendment, Date of Original Filed (Month/Day/Year)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Class A Common Stock	10/13/2026		M		2,000	A	$8.65	10,700	D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Option (right to buy)	$8.65	10/13/2026		M			2,000	(1)	01/18/2033	Class A Common Stock	2,000	$8.65	38,974	D

Explanation of Responses:

1. The options are fully vested and exercisable. The terms of the underlying option grant are as previously reported on the Reporting Person's Form 3 filed on November 5, 2025.

Remarks:

General Counsel, Chief Compliance Officer and Secretary

	Thomas P. Lynch	10/19/2026
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.
* Form 4: SEC 1474 (03-26)