BillionToOne holder David Tsao plans sale of 20K shares

A shareholder associated with BillionToOne, Inc. filed a Rule 144 notice to sell 20,000 Class A shares following a stock option exercise, with additional recent sales disclosed.

Available on EDGAR 09/09/2026 - 11:58 AM EDT Accepted by SEC EDGAR 09/09/2026 - 11:57 AM EDT Learn about SEC filing dates

Rhea-AI Filing Summary

BillionToOne, Inc. (BLLN) has a notice of proposed sale under Rule 144 for 20,000 shares of Class A common stock for the account of David Tsao, to be sold through Fidelity Brokerage Services LLC, in connection with a stock option exercise dated September 9, 2026.

The notice also lists multiple prior Class A share sales over the preceding three months by David Tsao and the Dt 2021 Irrevocable Trust, with David Tsao identified as an account stakeholder in the trust.

Key Figures

Shares to be sold: 20,000 shares Recent sale June 15, 2026 (Tsao): 20,000 shares Recent sale June 15, 2026 value (Tsao): $2,045,326.00 +3 more

6 metrics

Shares to be sold 20,000 shares Class A common stock proposed for sale for the account of David Tsao on September 9, 2026

Recent sale June 15, 2026 (Tsao) 20,000 shares Class A shares listed as sold for David Tsao on June 15, 2026

Recent sale June 15, 2026 value (Tsao) $2,045,326.00 Dollar amount listed alongside 20,000 Class A shares for June 15, 2026 sale by David Tsao

Recent sale July 13, 2026 (Tsao) 20,000 shares Class A shares listed as sold for David Tsao on July 13, 2026

Recent sale August 10, 2026 (Tsao) 10,000 shares Class A shares listed as sold for David Tsao on August 10, 2026

Recent sales by Dt 2021 Irrevocable Trust 3,500 shares on each of three dates Class A sales on June 15, July 13, and August 10, 2026

Key Terms

Rule 144, stock option exercise, Irrevocable Trust, attorney-in-fact

4 terms

Rule 144 regulatory

"See the definition of "person" in paragraph (a) of Rule 144."

Rule 144 is a U.S. securities regulation that sets conditions under which restricted or insider-held shares can be legally resold to the public, such as required holding periods, availability of public information, limits on how much can be sold at once, and certain filing requirements. For investors it matters because it determines when previously locked-up shares can enter the market — like a release valve that can increase supply, affect share price, and signal insider intent.

stock option exercise financial

"Class A | 09/09/2026 | Stock Option Exercise | Issuer"

A stock option exercise is the act of using a previously granted right to buy shares of a company's stock at a specific, predetermined price by paying that price and receiving the shares. It matters to investors because exercising changes who owns the shares (which can dilute existing ownership), can trigger taxable events and shift potential gains or losses, and affects voting power and the company’s outstanding share count—like turning a voucher into an actual product that becomes part of circulating supply.

Irrevocable Trust financial

"Dt 2021 Irrevocable Trust 1035 OBrien Drive Menlo Park CA 94025"

An irrevocable trust is a legal arrangement where an owner transfers assets into a separate entity managed by a trustee and gives up the power to modify or reclaim those assets. For investors it matters because putting stock or other holdings into such a trust can change who controls and benefits from the assets, affect taxes and creditor protection, and influence how easy it is to sell or value those holdings—like placing valuables in a locked safe overseen by someone else.

attorney-in-fact regulatory

"as attorney-in-fact for David Tsao."

An attorney-in-fact is the person or entity given legal authority through a power of attorney to act on behalf of another for specific tasks, such as signing documents, voting shares, or handling transactions. For investors, this matters because it lets a trusted representative make timely decisions or complete paperwork when the owner cannot, much like handing keys to someone to run errands on your behalf—so checks on scope and limits of that authority are important.

FAQ

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

What does BillionToOne, Inc. (BLLN) disclose in this Rule 144 notice?

The notice reports that 20,000 Class A shares of BillionToOne, Inc. are proposed to be sold for the account of David Tsao on September 9, 2026, in connection with a stock option exercise, with Fidelity Brokerage Services LLC listed as the broker.

How many BillionToOne (BLLN) shares is David Tsao planning to sell now?

The filing states that 20,000 Class A shares of BillionToOne, Inc. are to be sold for the account of David Tsao, tied to a stock option exercise dated September 9, 2026.

Which broker is handling the planned Rule 144 sale for BLLN shares?

The proposed sale of 20,000 Class A shares of BillionToOne, Inc. for the account of David Tsao is listed as being handled through Fidelity Brokerage Services LLC.

What recent sales of BillionToOne (BLLN) shares are disclosed for David Tsao?

The notice lists prior Class A sales for David Tsao of 20,000 shares on June 15, 2026, 20,000 shares on July 13, 2026, and 10,000 shares each on August 10 and August 25, 2026, each with associated dollar amounts.

What sales from the Dt 2021 Irrevocable Trust involving BLLN shares are reported?

The filing shows the Dt 2021 Irrevocable Trust sold 3,500 Class A shares on June 15, 2026, 3,500 shares on July 13, 2026, and 3,500 shares on August 10, 2026, with dollar amounts listed for each transaction.

What relationship does David Tsao have to the Dt 2021 Irrevocable Trust in this BLLN filing?

The remarks state that sales within the past 3 months occurred in the account of the Dt 2021 Irrevocable Trust by Icontrust LLC as trustee, and that David Tsao is an account stakeholder in the Dt 2021 Irrevocable Trust.

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

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Form 144 Filer Information	UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 Form 144 NOTICE OF PROPOSED SALE OF SECURITIES PURSUANT TO RULE 144 UNDER THE SECURITIES ACT OF 1933
FORM 144

144: Filer Information

Filer CIK	0002087127
Filer CCC	XXXXXXXX
Is this a LIVE or TEST Filing?	LIVE TEST
Submission Contact Information
Name
Phone
E-Mail Address

144: Issuer Information

Name of Issuer	BillionToOne, Inc.
SEC File Number	001-42934
Address of Issuer	1035 O'BRIEN DRIVE MENLO PARK CALIFORNIA 94025
Phone	650-460-2551
Name of Person for Whose Account the Securities are To Be Sold	Tsao David
See the definition of "person" in paragraph (a) of Rule 144. Information is to be given not only as to the person for whose account the securities are to be sold but also as to all other persons included in that definition. In addition, information shall be given as to sales by all persons whose sales are required by paragraph (e) of Rule 144 to be aggregated with sales for the account of the person filing this notice.
Relationship to Issuer	Officer
Relationship to Issuer	Director

144: Securities Information

Title of the Class of Securities To Be Sold	Name and Address of the Broker	Number of Shares or Other Units To Be Sold	Aggregate Market Value	Number of Shares or Other Units Outstanding	Approximate Date of Sale	Name the Securities Exchange
Class A	Fidelity Brokerage Services LLC 900 Salem Street Smithfield RI 02917	20000	2045326.00	42644388	09/09/2026	NASDAQ

Furnish the following information with respect to the acquisition of the securities to be sold and with respect to the payment of all or any part of the purchase price or other consideration therefor:

144: Securities To Be Sold

Title of the Class	Date you Acquired	Nature of Acquisition Transaction	Name of Person from Whom Acquired	Is this a Gift?	Date Donor Acquired	Amount of Securities Acquired	Date of Payment	Nature of Payment *
Class A	09/09/2026	Stock Option Exercise	Issuer			20000	09/09/2026	Cash

* If the securities were purchased and full payment therefor was not made in cash at the time of purchase, explain in the table or in a note thereto the nature of the consideration given. If the consideration consisted of any note or other obligation, or if payment was made in installments describe the arrangement and state when the note or other obligation was discharged in full or the last installment paid.

Furnish the following information as to all securities of the issuer sold during the past 3 months by the person for whose account the securities are to be sold.

144: Securities Sold During The Past 3 Months

Name and Address of Seller	Title of Securities Sold	Date of Sale	Amount of Securities Sold	Gross Proceeds
David Tsao 1035 OBrien Drive Menlo Park CA 94025	Class A	06/15/2026	20000	2045326.00
Dt 2021 Irrevocable Trust 1035 OBrien Drive Menlo Park CA 94025	Class A	06/15/2026	3500	355145.00
David Tsao 1035 OBrien Drive Menlo Park CA 94025	Class A	07/13/2026	20000	2497697.77
Dt 2021 Irrevocable Trust 1035 OBrien Drive Menlo Park CA 94025	Class A	07/13/2026	3500	439110.00
David Tsao 1035 OBrien Drive Menlo Park CA 94025	Class A	08/10/2026	10000	928600.00
Dt 2021 Irrevocable Trust 1035 OBrien Drive Menlo Park CA 94025	Class A	08/10/2026	3500	325010.00
David Tsao 1035 OBrien Drive Menlo Park CA 94025	Class A	08/25/2026	10000	1000000.00

144: Remarks and Signature

Remarks	Sales within the past 3 months occurred in the account of the Dt 2021 Irrevocable Trust by Icontrust Llc, trustee on the account. David Tsao is an account stakeholder in the Dt 2021 Irrevocable Trust.
Date of Notice	09/09/2026
Date of Plan Adoption or Giving of Instruction, If Relying on Rule 10b5-1	06/05/2026
ATTENTION:
The person for whose account the securities to which this notice relates are to be sold hereby represents by signing this notice that he does not know any material adverse information in regard to the current and prospective operations of the Issuer of the securities to be sold which has not been publicly disclosed. If such person has adopted a written trading plan or given trading instructions to satisfy Rule 10b5-1 under the Exchange Act, by signing the form and indicating the date that the plan was adopted or the instruction given, that person makes such representation as of the plan adoption or instruction date.
Signature	/s/ Jessica Spraker, as a duly authorized representative of Fidelity Brokerage Services LLC, as attorney-in-fact for David Tsao.
ATTENTION: Intentional misstatements or omission of facts constitute Federal Criminal Violations (See 18 U.S.C. 1001)