Sell4

BillionToOne, Inc.

BLLN

Total Value

$2.3M

Net $2.2M sold

Filing Date

Oct 7, 2026

11 transactions

Sales

$2.2M

11 transactions

Trade Summary

On Oct 5, 2026, Tsao David, Chief Technology Officer, Director, sold $2.3M of BillionToOne, Inc. (BLLN) across 11 transactions. The filing covers Class A Common Stock and reflects net selling of $2.2M. Reported prices ranged from $2.80 to $110.09. Insider transactions are sourced from SEC Form 4 disclosures and should be reviewed alongside company fundamentals and the insider's broader trading history.

Price at the Time of the Trade

BLLN daily price with the insider's sale marked at $108.15.

Sold in the lower half of the 6-month range · the stock trades 12% lower today.

Price data is delayed and provided for context only — not investment advice.

Insider Information

Name: Tsao David
Role: Chief Technology Officer, Director
Location: MENLO PARK, CA

Filing Details

Filing Date: Oct 7, 2026
Transaction Date: Oct 5, 2026
Accession Number: 0002087127-26-000015
Form Type: 4
Net Trading Amount: -$2.2M

Non-Derivative Transactions

Date	Security	Shares	Price	Type	Value
Oct 5, 2026	Class A Common Stock	10,000	$2.80	Exercise	$28.0K
Oct 5, 2026	Class A Common Stock	10,000	$2.80	Exercise	$28.0K
Oct 5, 2026	Class A Common Stock	866	$105.90	Sale	$91.7K
Oct 5, 2026	Class A Common Stock	1,909	$107.20	Sale	$204.6K
Oct 5, 2026	Class A Common Stock	4,284	$108.39	Sale	$464.4K
Oct 5, 2026	Class A Common Stock	2,921	$109.00	Sale	$318.4K
Oct 5, 2026	Class A Common Stock	20	$110.08	Sale	$2.2K
Oct 5, 2026	Class A Common Stock	555	$105.56	Sale	$58.6K
Oct 5, 2026	Class A Common Stock	400	$106.10	Sale	$42.4K
Oct 5, 2026	Class A Common Stock	2,200	$107.47	Sale	$236.4K
Oct 5, 2026	Class A Common Stock	4,916	$108.53	Sale	$533.6K
Oct 5, 2026	Class A Common Stock	1,829	$109.14	Sale	$199.6K
Oct 5, 2026	Class A Common Stock	100	$110.09	Sale	$11.0K

Derivative Transactions

Date	Security	Shares	Exercise Price	Type	Value
Oct 5, 2026	BLLN derivative	10,000	$2.80	Exercise	$28.0K
Oct 5, 2026	BLLN derivative	10,000	$2.80	Exercise	$28.0K

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Footnotes

(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.

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

94025

(City)

(State)

(Zip)

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

3. Date of Earliest Transaction (Month/Day/Year)
10/05/2026

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

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

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

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 as rendered by the SEC from accession 0002087127-26-000015.

BillionToOne, Inc.

Trade Summary

Price at the Time of the Trade

Company Information

Insider Information

Filing Details

Non-Derivative Transactions

Derivative Transactions

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Footnotes

SEC Form 4

SEC Filing

SEC Form 4

Price at the Time of the Trade