BillionToOne CEO and spouse sell 19,334 shares

The reported sales were made under separate Rule 10b5-1 plans adopted by Atay and his spouse on June 5 and June 7, 2026.

Rhea-AI Filing Summary

BillionToOne, Inc. (BLLN) Chairman and CEO Oguzhan Atay exercised 16,667 options at $2.80 per share on October 12, 2026, acquiring 16,667 Class A shares. The options were fully vested and exercisable.

The transactions reported sales of 19,334 Class A shares, including five direct sale transactions and 2,667 shares sold by Atay’s spouse. The direct sale rows reported weighted-average prices from $91.5712 to $96.3924 per share; the spouse’s sale had a $97.6100 weighted-average price. Atay’s transactions were under a Rule 10b5-1 plan adopted June 5, 2026; his spouse’s sale was under a separate plan adopted June 7, 2026. The spouse-held position following the sale was reported as 151,835 shares.

Insider Trade Summary 10b5-1

Exercise and sale activity reported; no spread calculated

Exercise and Sale 8 txns

Insider Atay Oguzhan

Role Chairman and CEO

Sold 19,334 shs ($1.82M)

Approx. gross sale proceeds $1.82M

Approx. exercise cost $47K

Type	Security	Shares	Price	Value
Exercise	Stock Option (right to buy) F9	16,667	$2.80	$47K
Exercise	Class A Common Stock F1	16,667	$2.80	$47K
Sale	Class A Common Stock F1, F2	1,961	$91.5712	$180K
Sale	Class A Common Stock F1, F3	2,553	$93.046	$238K
Sale	Class A Common Stock F1, F4	6,763	$93.647	$633K
Sale	Class A Common Stock F1, F5	3,869	$94.6133	$366K
Sale	Class A Common Stock F1, F6	1,521	$96.3924	$147K
Sale	Class A Common Stock F7, F8	2,667	$97.61	$260K

Holdings After Transaction: Stock Option (right to buy) — 476,962 contracts (Direct); Class A Common Stock — 0 shares (Direct); Class A Common Stock — 151,835 shares (Indirect, By spouse)

Footnotes (9)

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 5, 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 $91.250 to $92.170 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 $92.2596 to $93.255 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 reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $93.260 to $94.225 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. F5. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $94.265 to $95.205 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. F6. The reported price in Column 4 is a weighted average price. These shares were sold in multiple transactions at prices ranging from $95.945 to $96.765 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. F7. The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person's spouse on June 7, 2026.
8. F8. Represents shares held by the Reporting Person's spouse.
9. F9. The options are fully vested and exercisable.

Key Figures

Options exercised: 16,667 options Exercise price: $2.80 per share Reported shares sold: 19,334 Class A shares +4 more

7 metrics

Options exercised 16,667 options October 12, 2026

Exercise price $2.80 per share Options exercised October 12, 2026

Reported shares sold 19,334 Class A shares October 12, 2026 transactions

Weighted-average prices, direct sales $91.5712–$96.3924 per share Five reported direct sale transactions on October 12, 2026

Weighted-average price, spouse’s sale $97.6100 per share October 12, 2026

Shares following option transaction 476,962 shares Reported following the October 12, 2026 option transaction

Spouse-held shares following sale 151,835 shares Reported following the October 12, 2026 sale

Key Terms

Rule 10b5-1 trading plan, weighted average price, fully vested and exercisable

3 terms

Rule 10b5-1 trading plan regulatory

"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.

fully vested and exercisable financial

"The options are fully vested and exercisable"

FAQ

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

How many BLLN shares were sold in the reported transactions?

The transactions reported sales of 19,334 Class A shares on October 12, 2026: five direct sale transactions and 2,667 shares sold by Oguzhan Atay’s spouse. The spouse-held position following the sale was reported as 151,835 shares.

How many BLLN options did Oguzhan Atay exercise, and at what price?

Oguzhan Atay exercised 16,667 options at $2.80 per share on October 12, 2026, acquiring 16,667 Class A shares. The options were fully vested and exercisable.

What prices were reported for the BLLN sales?

The five direct sale rows reported weighted-average prices of $91.5712, $93.0460, $93.6470, $94.6133 and $96.3924 per share. The spouse’s sale reported a $97.6100 weighted-average price. Footnotes state that each reported price was a weighted average of multiple transactions.

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

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Available on EDGAR 10/14/2026 - 06:10 PM EDT Accepted by SEC EDGAR 10/14/2026 - 06:10 PM EDT 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^*

Atay Oguzhan

(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)
	Chairman and CEO

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
10/12/2026

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	10/12/2026		M(1)		16,667	A	$2.8	16,667	D
Class A Common Stock	10/12/2026		S(1)		1,961	D	$91.5712(2)	14,706	D
Class A Common Stock	10/12/2026		S(1)		2,553	D	$93.046(3)	12,153	D
Class A Common Stock	10/12/2026		S(1)		6,763	D	$93.647(4)	5,390	D
Class A Common Stock	10/12/2026		S(1)		3,869	D	$94.6133(5)	1,521	D
Class A Common Stock	10/12/2026		S(1)		1,521	D	$96.3924(6)	0	D
Class A Common Stock	10/12/2026		S(7)		2,667	D	$97.61	151,835	I	By spouse(8)

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	10/12/2026		M			16,667	(9)	06/07/2031	Class A Common Stock	16,667	$2.8	476,962	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 $91.250 to $92.170 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 $92.2596 to $93.255 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 $93.260 to $94.225 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 $94.265 to $95.205 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 $95.945 to $96.765 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 transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan adopted by the reporting person's spouse on June 7, 2026.

8. Represents shares held by the Reporting Person's spouse.

9. The options are fully vested and exercisable.

Remarks:

	/s/ Thomas P. Lynch, Attorney-in-Fact	10/14/2026
	** 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)