Does the Form 4 show Thomas P. Lynch’s BLLN share balance after these trades?

No. The reported entries describe the option exercises and sales, but the post-transaction share balances are not provided in the transaction details summarized here.

BillionToOne counsel sells 20K shares at ~$96–101

Q: What did BLLN insider Thomas P. Lynch report in this Form 4?

He reported exercising options for 20,000 shares of BillionToOne Class A Common Stock and selling 20,000 shares in multiple open-market transactions on September 8, 2026, all under a Rule 10b5-1 trading plan.

Q: What prices did Thomas P. Lynch receive for the BLLN shares sold?

He sold 20,000 shares of Class A Common Stock in multiple trades, with reported per-share prices including $96.4739, $98.9662 and up to $101.4077. Several prices are disclosed as weighted averages over specified intraday ranges.

Q: How many BLLN option shares did Thomas P. Lynch exercise in total?

He exercised options covering a total of 20,000 shares of BillionToOne Class A Common Stock on September 8, 2026, across four option series with different exercise prices and expiration dates.

BillionToOne’s general counsel exercised options for 20,000 shares and sold an equal number in Rule 10b5-1 plan trades around $96–$101 on September 8, 2026.

Filing Impact

(Neutral)

Filing Sentiment

(Neutral)

Form Type

Rhea-AI Filing Summary

BillionToOne, Inc. insider Thomas P. Lynch, the General Counsel, Chief Compliance Officer and Secretary, reported option exercises and related share sales on September 8, 2026. He exercised options covering 20,000 shares of Class A Common Stock at exercise prices of $8.65, $11.55, $17.12 and $30.78 per share, all from previously disclosed, fully vested grants.

On the same date, he sold a total of 20,000 shares of Class A Common Stock in a series of open-market transactions at prices generally around $96–$101 per share, with several reported as weighted-average prices over stated intraday ranges. All transactions were made under a Rule 10b5-1 trading plan adopted on June 8, 2026.

Insider Trade Summary 10b5-1

Exercise and Sale: 20,000 shares ($1.73M approx. pre-tax spread)

Exercise and Sale 21 txns

Insider Lynch Thomas P.

Role See Remarks

Sold 20,000 shs ($2.00M)

Approx. gross sale proceeds $2.00M

Approx. exercise cost $272K

Approx. pre-tax spread $1.73M

Type	Security	Shares	Price	Value
Exercise	Stock Option (right to buy) ^F12	11,042	$8.65	$96K
Exercise	Stock Option (right to buy) ^F12	3,969	$11.55	$46K
Exercise	Stock Option (right to buy) ^F12	1,663	$17.12	$28K
Exercise	Stock Option (right to buy) ^F12	3,326	$30.78	$102K
Exercise	Class A Common Stock ^F1	11,042	$8.65	$96K
Exercise	Class A Common Stock ^F1	3,969	$11.55	$46K
Exercise	Class A Common Stock ^F1	1,663	$17.12	$28K
Exercise	Class A Common Stock ^F1	3,326	$30.78	$102K
Sale	Class A Common Stock ^F1	38	$96.4739	$4K
Sale	Class A Common Stock ^{F1, F2}	1,944	$98.9662	$192K
Sale	Class A Common Stock ^{F1, F3}	8,285	$100.1228	$830K
Sale	Class A Common Stock ^{F1, F4}	775	$100.8289	$78K
Sale	Class A Common Stock ^{F1, F5}	614	$98.9986	$61K
Sale	Class A Common Stock ^{F1, F3}	2,997	$100.1135	$300K
Sale	Class A Common Stock ^{F1, F6}	358	$100.8234	$36K
Sale	Class A Common Stock ^{F1, F7}	385	$99.223	$38K
Sale	Class A Common Stock ^{F1, F8}	1,131	$100.3261	$113K
Sale	Class A Common Stock ^{F1, F9}	147	$101.4077	$15K
Sale	Class A Common Stock ^{F1, F2}	576	$98.8882	$57K
Sale	Class A Common Stock ^{F1, F10}	2,518	$100.1959	$252K
Sale	Class A Common Stock ^{F1, F11}	232	$100.9242	$23K

Holdings After Transaction: Stock Option (right to buy) — 124,400 contracts (Direct); Class A Common Stock — 700 shares (Direct)

Footnotes (12)

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 8, 2026.
F2. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $98.340 to $99.230 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 $99.585 to $100.565 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 $100.620 to $100.9125 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 $98.340 to $99.195 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 $100.720 to $100.9025 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 $98.830 to $99.825 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 $99.830 to $100.790 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 $100.890 to $101.870 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 $99.670 to $100.550 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 reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $100.725 to $101.650 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.
F12. 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 sold: 20,000 shares Shares acquired via option exercise: 20,000 shares Option exercise price 1: $8.65 per share +5 more

8 metrics

Shares sold 20,000 shares Total Class A Common Stock sold on September 8, 2026

Shares acquired via option exercise 20,000 shares Class A Common Stock received from option exercises on September 8, 2026

Option exercise price 1 $8.65 per share One option series exercised into Class A Common Stock

Option exercise price 2 $11.55 per share Second option series exercised into Class A Common Stock

Option exercise price 3 $17.12 per share Third option series exercised into Class A Common Stock

Option exercise price 4 $30.78 per share Fourth option series exercised into Class A Common Stock

Lowest reported sale price $96.4739 per share One Class A Common Stock sale on September 8, 2026

Highest reported sale price $101.4077 per share One Class A Common Stock sale on September 8, 2026

Key Terms

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

4 terms

Rule 10b5-1 trading plan regulatory

"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.

weighted average price financial

"The 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.

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.

fully vested and exercisable financial

"The options are fully vested and exercisable."

FAQ

What did BLLN insider Thomas P. Lynch report in this Form 4?

He reported exercising options for 20,000 shares of BillionToOne Class A Common Stock and selling 20,000 shares in multiple open-market transactions on September 8, 2026, all under a Rule 10b5-1 trading plan.

At what prices were Thomas P. Lynch’s BLLN options exercised?

He exercised options into Class A Common Stock at exercise prices of $8.65, $11.55, $17.12 and $30.78 per share on September 8, 2026, from fully vested option grants previously reported.

What prices did Thomas P. Lynch receive for the BLLN shares sold?

He sold 20,000 shares of Class A Common Stock in multiple trades, with reported per-share prices including $96.4739, $98.9662 and up to $101.4077. Several prices are disclosed as weighted averages over specified intraday ranges.

Were the BLLN trades 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 Thomas P. Lynch on June 8, 2026.

How many BLLN option shares did Thomas P. Lynch exercise in total?

He exercised options covering a total of 20,000 shares of BillionToOne Class A Common Stock on September 8, 2026, across four option series with different exercise prices and expiration dates.

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Available on EDGAR 09/10/2026 - 07:45 PM Accepted by SEC EDGAR 09/10/2026 - 07:44 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^*

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)
09/08/2026

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	09/08/2026		M⁽¹⁾		11,042	A	$8.65	11,742	D
Class A Common Stock	09/08/2026		M⁽¹⁾		3,969	A	$11.55	15,711	D
Class A Common Stock	09/08/2026		M⁽¹⁾		1,663	A	$17.12	17,374	D
Class A Common Stock	09/08/2026		M⁽¹⁾		3,326	A	$30.78	20,700	D
Class A Common Stock	09/08/2026		S⁽¹⁾		38	D	$96.4739	20,662	D
Class A Common Stock	09/08/2026		S⁽¹⁾		1,944	D	$98.9662⁽²⁾	18,718	D
Class A Common Stock	09/08/2026		S⁽¹⁾		8,285	D	$100.1228⁽³⁾	10,433	D
Class A Common Stock	09/08/2026		S⁽¹⁾		775	D	$100.8289⁽⁴⁾	9,658	D
Class A Common Stock	09/08/2026		S⁽¹⁾		614	D	$98.9986⁽⁵⁾	9,044	D
Class A Common Stock	09/08/2026		S⁽¹⁾		2,997	D	$100.1135⁽³⁾	6,047	D
Class A Common Stock	09/08/2026		S⁽¹⁾		358	D	$100.8234⁽⁶⁾	5,689	D
Class A Common Stock	09/08/2026		S⁽¹⁾		385	D	$99.223⁽⁷⁾	5,304	D
Class A Common Stock	09/08/2026		S⁽¹⁾		1,131	D	$100.3261⁽⁸⁾	4,173	D
Class A Common Stock	09/08/2026		S⁽¹⁾		147	D	$101.4077⁽⁹⁾	4,026	D
Class A Common Stock	09/08/2026		S⁽¹⁾		576	D	$98.8882⁽²⁾	3,450	D
Class A Common Stock	09/08/2026		S⁽¹⁾		2,518	D	$100.1959⁽¹⁰⁾	932	D
Class A Common Stock	09/08/2026		S⁽¹⁾		232	D	$100.9242⁽¹¹⁾	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)
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)	$8.65	09/08/2026		M			11,042	⁽¹²⁾	01/18/2033	Class A Common Stock	11,042	$8.65	68,358	D
Stock Option (right to buy)	$11.55	09/08/2026		M			3,969	⁽¹²⁾	10/17/2033	Class A Common Stock	3,969	$11.55	11,031	D
Stock Option (right to buy)	$17.12	09/08/2026		M			1,663	⁽¹²⁾	10/16/2034	Class A Common Stock	1,663	$17.12	8,337	D
Stock Option (right to buy)	$30.78	09/08/2026		M			3,326	⁽¹²⁾	09/30/2035	Class A Common Stock	3,326	$30.78	36,674	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 8, 2026.

2. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $98.340 to $99.230 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 $99.585 to $100.565 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 $100.620 to $100.9125 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 $98.340 to $99.195 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 $100.720 to $100.9025 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 $98.830 to $99.825 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 $99.830 to $100.790 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 $100.890 to $101.870 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 $99.670 to $100.550 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 reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $100.725 to $101.650 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.

12. 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	09/10/2026
	** 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

BillionToOne counsel sells 20K shares at ~$96–101

Rhea-AI Filing Summary

Positive

Negative