BillionToOne CTO sells $1M in stock, exercises options

Rhea-AI Filing Summary

BillionToOne, Inc. (BLLN) director and Chief Technology Officer David Tsao reported an option exercise and related share sale. On 2026-08-25, he exercised 10,000 stock options for Class A Common Stock at $2.80 per share, receiving 10,000 shares, and on the same date sold 10,000 shares at $100.00 per share. Following the exercise, he held 580,000 stock options for Class A Common Stock. These transactions were effected pursuant to a Rule 10b5-1 trading plan adopted on March 6, 2026, and the options exercised were fully vested and exercisable.

Insider Trade Summary 10b5-1

Exercise and Sale: 10,000 shares ($972K approx. pre-tax spread)

Exercise and Sale 3 txns

Insider Tsao David

Role Chief Technology Officer

Sold 10,000 shs ($1.00M)

Approx. gross sale proceeds $1.00M

Approx. exercise cost $28K

Approx. pre-tax spread $972K

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

Holdings After Transaction: Stock Option (right to buy) — 580,000 shares (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 March 6, 2026.
2. F2. The options are fully vested and exercisable.

Key Figures

Options exercised: 10,000 shares of Class A Common Stock Exercise price: $2.80 per share Shares sold: 10,000 shares of Class A Common Stock +3 more

6 metrics

Options exercised 10,000 shares of Class A Common Stock Stock Option (right to buy) exercised on 2026-08-25

Exercise price $2.80 per share Exercise of 10,000 stock options on 2026-08-25

Shares sold 10,000 shares of Class A Common Stock Sale transaction on 2026-08-25

Sale price $100.00 per share Sale of 10,000 shares of Class A Common Stock on 2026-08-25

Options held after transaction 580,000 stock options Post-transaction derivative holdings for Class A Common Stock

Rule 10b5-1 plan adoption date March 6, 2026 Trading plan under which the reported transactions were effected

Key Terms

Rule 10b5-1 trading plan, Stock Option (right to buy), Class A Common Stock

3 terms

Rule 10b5-1 trading plan financial

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

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.

Stock Option (right to buy) financial

"security_title: Stock Option (right to buy)"

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

What insider transactions did BLLN CTO David Tsao report on this Form 4?

David Tsao exercised 10,000 stock options for Class A Common Stock at $2.80 per share and sold 10,000 shares of Class A Common Stock at $100.00 per share on 2026-08-25, in transactions reported for BillionToOne, Inc. (BLLN).

At what prices did David Tsao exercise and sell BLLN shares?

He exercised options to acquire 10,000 shares at an exercise price of $2.80 per share and sold 10,000 shares of Class A Common Stock at $100.00 per share, all dated 2026-08-25.

How many BillionToOne (BLLN) options does David Tsao hold after these transactions?

After the reported exercise, David Tsao held 580,000 stock options for Class A Common Stock, as shown by the post-transaction derivative holding on the Form 4.

Were David Tsao’s BLLN transactions under a Rule 10b5-1 trading plan?

Yes. The Form 4 states the transactions were effected pursuant to a Rule 10b5-1 trading plan adopted by David Tsao on March 6, 2026.

Were the options David Tsao exercised in BLLN fully vested?

Yes. A footnote explains that the options are fully vested and exercisable, meaning the 10,000 options exercised on 2026-08-25 were already fully vested.

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

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Available on EDGAR 08/28/2026 - 08:45 AM Accepted by SEC EDGAR 08/27/2026 - 08:19 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)
08/25/2026

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	08/25/2026		M(1)		10,000	A	$2.8	11,000	D
Class A Common Stock	08/25/2026		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	08/25/2026		M			10,000	(2)	06/07/2031	Class A Common Stock	10,000	$2.8	580,000	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 March 6, 2026.

2. The options are fully vested and exercisable.

Remarks:

	/s/ Thomas P. Lynch, Attorney-in-Fact	08/27/2026
	** 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)