BillionToOne counsel sells 35K shares near $110

BillionToOne’s General Counsel exercised options into 35,112 BLLN shares and sold the same amount under a pre-arranged Rule 10b5-1 trading plan.

Rhea-AI Filing Summary

BillionToOne, Inc. (BLLN) insider Thomas P. Lynch, the company’s General Counsel, Chief Compliance Officer and Secretary, reported option exercises and related share sales in Class A Common Stock on September 17, 2026. He exercised stock options covering 35,112 shares at exercise prices from $8.65 to $30.78 per share, receiving the same number of Class A shares. He then sold 35,112 shares of Class A Common Stock in multiple open-market or private transactions at weighted average prices around $110 per share, with sale-price ranges detailed in the footnotes. All transactions were effected pursuant to a Rule 10b5-1 trading plan adopted on June 8, 2026, and the options exercised were fully vested and exercisable.

Insider Trade Summary 10b5-1

Exercise and Sale: 35,112 shares ($3.40M approx. pre-tax spread)

Exercise and Sale 12 txns

Insider Lynch Thomas P.

Role See Remarks

Sold 35,112 shs ($3.87M)

Approx. gross sale proceeds $3.87M

Approx. exercise cost $478K

Approx. pre-tax spread $3.40M

Type	Security	Shares	Price	Value
Exercise	Stock Option (right to buy) F4	19,384	$8.65	$168K
Exercise	Stock Option (right to buy) F4	6,968	$11.55	$80K
Exercise	Stock Option (right to buy) F4	2,920	$17.12	$50K
Exercise	Stock Option (right to buy) F4	5,840	$30.78	$180K
Exercise	Class A Common Stock F1	19,384	$8.65	$168K
Exercise	Class A Common Stock F1	6,968	$11.55	$80K
Exercise	Class A Common Stock F1	2,920	$17.12	$50K
Exercise	Class A Common Stock F1	5,840	$30.78	$180K
Sale	Class A Common Stock F1, F2	19,384	$110.3587	$2.14M
Sale	Class A Common Stock F1, F3	6,968	$110.2986	$769K
Sale	Class A Common Stock F1, F3	2,920	$110.3083	$322K
Sale	Class A Common Stock F1, F2	5,840	$110.2931	$644K

Holdings After Transaction: Stock Option (right to buy) — 89,288 contracts (Direct); Class A Common Stock — 700 shares (Direct)

Footnotes (4)

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 8, 2026.
2. F2. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $110.000 to $110.970 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.
3. F3. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $110.000 to $110.890 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. F4. 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: 35,112 shares Options exercised: 35,112 shares Exercise price range: $8.65–$30.78 per share +3 more

6 metrics

Shares sold 35,112 shares Class A Common Stock sold on September 17, 2026

Options exercised 35,112 shares Stock options converted into Class A Common Stock on September 17, 2026

Exercise price range $8.65–$30.78 per share Exercise prices of stock options exercised by the insider

Sale price range (block F2) $110.00–$110.97 per share Price range for certain weighted-average sale transactions

Sale price range (block F3) $110.00–$110.89 per share Price range for additional weighted-average sale transactions

Rule 10b5-1 plan adoption date June 8, 2026 Date the trading plan governing these transactions was adopted

Key Terms

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

4 terms

Rule 10b5-1 trading plan regulatory

"transactions 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.

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.

Stock Option (right to buy) financial

"security title is Stock Option (right to buy)"

Class A Common Stock financial

"underlying security title is 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 did BillionToOne (BLLN) insider Thomas P. Lynch report on this Form 4?

He reported exercising stock options for 35,112 shares of Class A Common Stock and selling 35,112 shares on September 17, 2026, in multiple open-market or private transactions under a Rule 10b5-1 trading plan.

How many BLLN shares did Thomas P. Lynch sell on September 17, 2026?

He sold a total of 35,112 shares of BillionToOne Class A Common Stock, reported across four sale transactions of 19,384; 6,968; 2,920; and 5,840 shares, respectively.

At what prices were the BLLN shares sold in this Form 4?

The reported prices are weighted averages. The sales occurred in ranges of $110.00–$110.97 per share and $110.00–$110.89 per share, with specific weighted average prices per block around $110.30 per share, as described in the footnotes.

Were Thomas P. Lynch’s BLLN trades made under a Rule 10b5-1 plan?

Yes. The filing states the transactions were effected under a Rule 10b5-1 trading plan adopted by the reporting person on June 8, 2026, indicating the trades were pre-arranged.

What options did Thomas P. Lynch exercise for BLLN stock?

He exercised fully vested stock options for 35,112 shares at exercise prices of $8.65, $11.55, $17.12, and $30.78 per share, with expiration dates from January 18, 2033 through September 30, 2035.

What role does Thomas P. Lynch hold at BillionToOne (BLLN)?

According to the filing remarks, Thomas P. Lynch serves as General Counsel, Chief Compliance Officer and Secretary of BillionToOne, Inc.

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

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Available on EDGAR 09/21/2026 - 07:00 PM Accepted by SEC EDGAR 09/21/2026 - 07:00 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^*

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)
09/17/2026

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	09/17/2026		M(1)		19,384	A	$8.65	20,084	D
Class A Common Stock	09/17/2026		M(1)		6,968	A	$11.55	27,052	D
Class A Common Stock	09/17/2026		M(1)		2,920	A	$17.12	29,972	D
Class A Common Stock	09/17/2026		M(1)		5,840	A	$30.78	35,812	D
Class A Common Stock	09/17/2026		S(1)		19,384	D	$110.3587(2)	16,428	D
Class A Common Stock	09/17/2026		S(1)		6,968	D	$110.2986(3)	9,460	D
Class A Common Stock	09/17/2026		S(1)		2,920	D	$110.3083(3)	6,540	D
Class A Common Stock	09/17/2026		S(1)		5,840	D	$110.2931(2)	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)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares
Stock Option (right to buy)	$8.65	09/17/2026		M			19,384	(4)	01/18/2033	Class A Common Stock	19,384	$8.65	48,974	D
Stock Option (right to buy)	$11.55	09/17/2026		M			6,968	(4)	10/17/2033	Class A Common Stock	6,968	$11.55	4,063	D
Stock Option (right to buy)	$17.12	09/17/2026		M			2,920	(4)	10/16/2034	Class A Common Stock	2,920	$17.12	5,417	D
Stock Option (right to buy)	$30.78	09/17/2026		M			5,840	(4)	09/30/2035	Class A Common Stock	5,840	$30.78	30,834	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 $110.000 to $110.970 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.

3. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $110.000 to $110.890 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 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	09/21/2026
	** 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)