BillionToOne CTO sells 20,000 shares

BillionToOne’s chief technology officer exercised options and sold 20,000 shares under a Rule 10b5-1 plan.

Rhea-AI Filing Summary

BillionToOne, Inc. (BLLN) reported that Chief Technology Officer David Tsao exercised options to acquire 20,000 shares of Class A Common Stock at an exercise price of $2.80 per share on September 9, 2026, and sold 20,000 shares the same day in two transactions at $97.54 and $100.00 per share. These transactions were carried out under a Rule 10b5-1 trading plan adopted on June 5, 2026, and the options exercised were fully vested and exercisable.

Insider Trade Summary 10b5-1

Exercise and Sale: 20,000 shares ($1.92M approx. pre-tax spread)

Exercise and Sale 6 txns

Insider Tsao David

Role Chief Technology Officer

Sold 20,000 shs ($1.98M)

Approx. gross sale proceeds $1.98M

Approx. exercise cost $56K

Approx. pre-tax spread $1.92M

Type	Security	Shares	Price	Value
Exercise	Stock Option (right to buy) F2	10,000	$2.80	$28K
Exercise	Stock Option (right to buy) F2	10,000	$2.80	$28K
Exercise	Class A Common Stock F1	10,000	$2.80	$28K
Exercise	Class A Common Stock F1	10,000	$2.80	$28K
Sale	Class A Common Stock F1	10,000	$97.54	$975K
Sale	Class A Common Stock F1	10,000	$100.00	$1.00M

Holdings After Transaction: Stock Option (right to buy) — 560,000 contracts (Direct); Class A Common Stock — 1,000 shares (Direct)

Footnotes (2)

1. F1. The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on June 5, 2026.
2. F2. The options are fully vested and exercisable.

Key Figures

Shares acquired via option exercise: 20,000 shares Option exercise price: $2.80 per share Shares sold: 20,000 shares +3 more

6 metrics

Shares acquired via option exercise 20,000 shares Class A Common Stock acquired by exercising stock options on September 9, 2026

Option exercise price $2.80 per share Exercise price for 20,000 options exercised on September 9, 2026

Shares sold 20,000 shares Class A Common Stock sold on September 9, 2026

Sale prices $97.54 and $100.00 per share Prices for two 10,000-share sales of Class A Common Stock

Rule 10b5-1 plan adoption date June 5, 2026 Date David Tsao adopted the trading plan governing these transactions

Option expiration date June 7, 2031 Expiration date of the options that were exercised

Key Terms

Rule 10b5-1 trading plan, fully vested and exercisable, Class A Common Stock

3 terms

Rule 10b5-1 trading plan regulatory

"The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted"

A Rule 10b5-1 trading plan is a pre-arranged schedule that allows company insiders to buy or sell stock at specific times, even if they have inside information. It helps prevent accusations of unfair trading by making these transactions look planned and transparent, rather than sneaky or illegal.

fully vested and exercisable financial

"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.

What insider transactions did BLLN’s CTO report on September 9, 2026?

David Tsao exercised options for 20,000 shares of Class A Common Stock at $2.80 per share and sold 20,000 shares the same day in two trades at $97.54 and $100.00 per share.

Were the BLLN insider trades by the CTO made under a Rule 10b5-1 plan?

Yes. The filing states the transactions were effected pursuant to a Rule 10b5-1 trading plan adopted by David Tsao on June 5, 2026.

What stock option terms applied to the BLLN options exercised by the CTO?

David Tsao exercised stock options covering 20,000 shares of Class A Common Stock at an exercise price of $2.80 per share, with the options described as fully vested and exercisable and expiring on June 7, 2031.

How many BLLN shares did the CTO sell and at what prices?

He sold a total of 20,000 shares of Class A Common Stock on September 9, 2026, in two transactions: 10,000 shares at $97.54 per share and 10,000 shares at $100.00 per share.

Does the Form 4 disclose remaining BLLN holdings for the CTO after these transactions?

No specific post-transaction share holdings are stated in the reported data; only the option exercises and the 20,000 shares sold on September 9, 2026 are described.

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

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Available on EDGAR 09/11/2026 - 06:01 PM Accepted by SEC EDGAR 09/11/2026 - 06:01 PM 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).

X

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^*

Tsao David

(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)

X	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	Chief Technology Officer

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
09/09/2026

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	09/09/2026		M(1)		10,000	A	$2.8	11,000	D
Class A Common Stock	09/09/2026		M(1)		10,000	A	$2.8	21,000	D
Class A Common Stock	09/09/2026		S(1)		10,000	D	$97.54	11,000	D
Class A Common Stock	09/09/2026		S(1)		10,000	D	$100	1,000	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)	$2.8	09/09/2026		M			10,000	(2)	06/07/2031	Class A Common Stock	10,000	$2.8	570,000	D
Stock Option (right to buy)	$2.8	09/09/2026		M			10,000	(2)	06/07/2031	Class A Common Stock	10,000	$2.8	560,000	D

Explanation of Responses:

1. The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person on June 5, 2026.

2. The options are fully vested and exercisable.

Remarks:

	/s/ Thomas P. Lynch, Attorney-in-Fact	09/11/2026
	** 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)