BillionToOne (BLLN) CPO sells 8,000 shares under Rule 10b5-1 plan

Rhea-AI Filing Summary

BillionToOne, Inc. Chief Product Officer Sakakibara Shan Riku reported open-market sales of 8,000 shares of Class A Common Stock on June 8, 2026. The transactions were executed in two tranches at prices of $100.00 and $96.45 per share under a pre-arranged Rule 10b5-1 trading plan.

The filing indicates these were routine, pre-planned dispositions, and the executive continues to hold a substantially larger direct equity position after the sales.

Insider Trade Summary 10b5-1

Net Seller: 8,000 shares ($785,800)

Net Sell 2 txns

Insider Sakakibara Shan Riku

Role Chief Product Officer

Sold 8,000 shs ($786K)

Type	Security	Shares	Price	Value
Sale	Class A Common Stock	4,000	$96.45	$386K
Sale	Class A Common Stock	4,000	$100.00	$400K

Holdings After Transaction: Class A Common Stock — 216,000 shares (Direct, null)

Footnotes (1)

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Key Figures

Shares sold: 8,000 shares First sale block: 4,000 shares at $100.00/share Second sale block: 4,000 shares at $96.45/share +3 more

6 metrics

Shares sold 8,000 shares Total Class A shares sold on June 8, 2026

First sale block 4,000 shares at $100.00/share Open-market sale of Class A Common Stock

Second sale block 4,000 shares at $96.45/share Open-market sale of Class A Common Stock

Net share change -8,000 shares Net-sell direction from transaction summary

Transaction count 2 sales Non-derivative open-market transactions on June 8, 2026

Rule 10b5-1 plan adoption date March 6, 2026 Date CPO adopted trading plan used for these sales

Key Terms

Rule 10b5-1 trading plan, open-market sale, Class A Common Stock, Form 4

4 terms

Rule 10b5-1 trading plan regulatory

"The transactions reported on this Form 4 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.

open-market sale financial

"transaction_action: open-market sale, transaction_code_description: Sale in open market"

An open-market sale is when a shareholder sells existing shares directly on a public exchange to any willing buyer, rather than through a private deal. Think of it like putting goods on a busy market stall where price is set by supply and demand; for investors it matters because such sales increase available supply, can put short-term downward pressure on the stock price, and signal changes in liquidity or investor confidence.

Class A Common Stock financial

"security_title: Class A Common Stock for each reported transaction"

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.

Form 4 regulatory

"The transactions reported on this Form 4 were effected pursuant to a Rule 10b5-1 trading plan"

Form 4 is a official document that company insiders, such as executives or major shareholders, file with regulators whenever they buy or sell company shares. It provides transparency about how those with inside knowledge are trading, helping investors see if insiders are confident in the company's prospects or may be selling for personal reasons. This information can influence investor decisions by revealing insiders' perspectives on the company's value.

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Form 4 Insider Transactions: What Each Field Means →

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^*

Sakakibara Shan Riku

(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)
	Chief Product Officer

2a. Foreign Trading Symbol

3. Date of Earliest Transaction (Month/Day/Year)
06/08/2026

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)
			Code	V	Amount	(A) or (D)	Price
Class A Common Stock	06/08/2026		S(1)		4,000	D	$96.45	216,000	D
Class A Common Stock	06/08/2026		S(1)		4,000	D	$100	212,000	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)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

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 March 6, 2026.

Remarks:

	/s/ Thomas P. Lynch, Attorney-in-Fact	06/10/2026
	** 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)

FAQ

What insider transaction did BillionToOne (BLLN) report in this Form 4?

BillionToOne reported that Chief Product Officer Sakakibara Shan Riku sold 8,000 shares of Class A Common Stock. The sales occurred in two open-market transactions on June 8, 2026, and were executed pursuant to a pre-arranged Rule 10b5-1 trading plan.

How many BillionToOne (BLLN) shares did the CPO sell and at what prices?

The CPO sold a total of 8,000 Class A shares. One 4,000-share block was sold at $100.00 per share and another 4,000-share block at $96.45 per share, reflecting two separate open-market sales on June 8, 2026.

Was the BillionToOne (BLLN) insider sale 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 March 6, 2026. Such pre-arranged plans automate trading and can reduce the significance of timing for interpreting insider sentiment.

What role does the reporting person hold at BillionToOne (BLLN)?

The reporting person, Sakakibara Shan Riku, serves as Chief Product Officer at BillionToOne, Inc. This executive role focuses on leading product strategy and development, and the Form 4 reflects their personal equity transactions in the company’s Class A Common Stock.

Did the BillionToOne (BLLN) CPO retain a stake after selling shares?

Yes. The Form 4 shows that after completing the 8,000-share sale, the CPO continued to hold a significantly larger number of Class A shares directly. This indicates the reported trades represent only a portion of the executive’s overall equity position.