BillionToOne CTO exercises options, sells 20K shares

Q: How many BLLN shares did David Tsao sell?

David Tsao sold 20,000 shares of Class A common stock in 11 transactions on October 5, 2026. One reported transaction was 4,284 shares at a weighted average price of $108.3930 per share. The common-stock sales were under a Rule 10b5-1 trading plan adopted June 5, 2026.

Q: How many BLLN shares did David Tsao acquire through option exercises?

David Tsao exercised options to acquire 20,000 Class A common shares at $2.80 per share on October 5, 2026. The options were fully vested and exercisable and expire June 7, 2031.

The reported Class A share acquisitions and sales were under a Rule 10b5-1 plan adopted June 5, 2026.

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Rhea-AI Filing Summary

BillionToOne, Inc. (BLLN) Chief Technology Officer David Tsao exercised options to acquire 20,000 shares of Class A common stock at $2.80 per share on October 5, 2026. He sold 20,000 shares that day in 11 transactions. The common-stock acquisitions and sales were reported under a Rule 10b5-1 trading plan adopted June 5, 2026. The options were fully vested and exercisable and expire June 7, 2031.

Insider Trade Summary 10b5-1

Exercise and Sale: 20,000 shares ($2.11M approx. pre-tax spread)

Exercise and Sale 15 txns

Insider Tsao David

Role Chief Technology Officer

Sold 20,000 shs ($2.16M)

Approx. gross sale proceeds $2.16M

Approx. exercise cost $56K

Approx. pre-tax spread $2.11M

Type	Security	Shares	Price	Value
Exercise	Stock Option (right to buy) ^F11	10,000	$2.80	$28K
Exercise	Stock Option (right to buy) ^F11	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, F2}	866	$105.9004	$92K
Sale	Class A Common Stock ^{F1, F3}	1,909	$107.195	$205K
Sale	Class A Common Stock ^{F1, F4}	4,284	$108.393	$464K
Sale	Class A Common Stock ^{F1, F5}	2,921	$109.0031	$318K
Sale	Class A Common Stock ^F1	20	$110.08	$2K
Sale	Class A Common Stock ^{F1, F6}	555	$105.5587	$59K
Sale	Class A Common Stock ^{F1, F7}	400	$106.1038	$42K
Sale	Class A Common Stock ^{F1, F8}	2,200	$107.4705	$236K
Sale	Class A Common Stock ^{F1, F9}	4,916	$108.5342	$534K
Sale	Class A Common Stock ^{F1, F10}	1,829	$109.1445	$200K
Sale	Class A Common Stock ^F1	100	$110.09	$11K

Holdings After Transaction: Stock Option (right to buy) — 536,667 contracts (Direct); Class A Common Stock — 1,000 shares (Direct)

Footnotes (11)

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.
F2. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $105.505 to $106.350 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
F3. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $106.730 to $107.700 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
F4. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $107.7354 to $108.710 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
F5. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $108.740 to $109.480 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
F6. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $104.880 to $105.720 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
F7. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $105.890 to $106.180 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
F8. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $107.010 to $107.970 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
F9. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $108.040 to $109.030 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
F10. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $109.040 to $109.500 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.
F11. The options are fully vested and exercisable.

Key Figures

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

6 metrics

Shares acquired through option exercise 20,000 shares October 5, 2026

Exercise price $2.80 per share Options exercised on October 5, 2026

Shares sold 20,000 shares 11 transactions on October 5, 2026

Weighted average sale price $108.3930 per share 4,284 shares sold

Rule 10b5-1 plan adoption date June 5, 2026 Plan covering the reported common-stock acquisitions and sales

Option expiration date June 7, 2031 Reported options

Key Terms

Rule 10b5-1 trading plan, weighted average price, Stock Option (right to buy)

3 terms

Rule 10b5-1 trading plan regulatory

"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.

weighted average price financial

"reported price in Column 4 is a weighted average price"

Weighted average price is the average price of a security where each trade or component is counted according to its size, so bigger trades pull the average more than smaller ones. Think of it like calculating the average cost of a grocery haul where items you bought more of have greater influence on the final per-item cost. Investors use it to understand the true average price paid or received, judge execution quality, and compare trading performance against market movement.

Stock Option (right to buy) financial

"Stock Option (right to buy)"

FAQ

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

How many BLLN shares did David Tsao sell?

David Tsao sold 20,000 shares of Class A common stock in 11 transactions on October 5, 2026. One reported transaction was 4,284 shares at a weighted average price of $108.3930 per share. The common-stock sales were under a Rule 10b5-1 trading plan adopted June 5, 2026.

How many BLLN shares did David Tsao acquire through option exercises?

David Tsao exercised options to acquire 20,000 Class A common shares at $2.80 per share on October 5, 2026. The options were fully vested and exercisable and expire June 7, 2031.

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

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Available on EDGAR 10/07/2026 - 07:57 PM Accepted by SEC EDGAR 10/07/2026 - 07:56 PM

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^*

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)
10/05/2026

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)
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	Code	V	Amount	(A) or (D)	Price		6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
Class A Common Stock	10/05/2026		M⁽¹⁾		10,000	A	$2.8	11,000	D
Class A Common Stock	10/05/2026		M⁽¹⁾		10,000	A	$2.8	21,000	D
Class A Common Stock	10/05/2026		S⁽¹⁾		866	D	$105.9004⁽²⁾	20,134	D
Class A Common Stock	10/05/2026		S⁽¹⁾		1,909	D	$107.195⁽³⁾	18,225	D
Class A Common Stock	10/05/2026		S⁽¹⁾		4,284	D	$108.393⁽⁴⁾	13,941	D
Class A Common Stock	10/05/2026		S⁽¹⁾		2,921	D	$109.0031⁽⁵⁾	11,020	D
Class A Common Stock	10/05/2026		S⁽¹⁾		20	D	$110.08	11,000	D
Class A Common Stock	10/05/2026		S⁽¹⁾		555	D	$105.5587⁽⁶⁾	10,445	D
Class A Common Stock	10/05/2026		S⁽¹⁾		400	D	$106.1038⁽⁷⁾	10,045	D
Class A Common Stock	10/05/2026		S⁽¹⁾		2,200	D	$107.4705⁽⁸⁾	7,845	D
Class A Common Stock	10/05/2026		S⁽¹⁾		4,916	D	$108.5342⁽⁹⁾	2,929	D
Class A Common Stock	10/05/2026		S⁽¹⁾		1,829	D	$109.1445⁽¹⁰⁾	1,100	D
Class A Common Stock	10/05/2026		S⁽¹⁾		100	D	$110.09	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)
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)	Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares	8. Price of Derivative Security (Instr. 5)		10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
Stock Option (right to buy)	$2.8	10/05/2026		M			10,000	⁽¹¹⁾	06/07/2031	Class A Common Stock	10,000	$2.8	546,667	D
Stock Option (right to buy)	$2.8	10/05/2026		M			10,000	⁽¹¹⁾	06/07/2031	Class A Common Stock	10,000	$2.8	536,667	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 reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $105.505 to $106.350 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

3. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $106.730 to $107.700 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

4. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $107.7354 to $108.710 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

5. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $108.740 to $109.480 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

6. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $104.880 to $105.720 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

7. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $105.890 to $106.180 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

8. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $107.010 to $107.970 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

9. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $108.040 to $109.030 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

10. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $109.040 to $109.500 per share, inclusive. The holder undertakes to provide, upon written request, full information regarding the number of shares sold at each separate price within the range set forth in this footnote.

11. The options are fully vested and exercisable.

Remarks:

	/s/ Thomas P. Lynch, Attorney-in-Fact	10/07/2026
	** 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)

Source: View Original Filing on SEC EDGAR