BillionToOne's David Tsao Proposes Sale of 3,333 Shares

The proposed shares were acquired from the issuer through a stock option exercise for cash, and prior sale entries also include the Dt 2021 Irrevocable Trust.

Available on EDGAR 09/24/2026 - 05:03 PM EDT Accepted by SEC EDGAR 09/24/2026 - 05:02 PM EDT Learn about SEC filing dates

Rhea-AI Filing Summary

BillionToOne, Inc. is named as issuer in David Tsao’s notice to sell 3,333 Class A shares through Fidelity Brokerage Services LLC on Nasdaq on September 24, 2026, at an aggregate market value of $416,625.00. The shares were acquired from the issuer through a stock option exercise for cash.

The notice also lists prior Class A sales by David Tsao and the Dt 2021 Irrevocable Trust. Its remarks identify Icontrust LLC as trustee for the trust account and Tsao as a stakeholder.

Key Figures

Class A shares proposed for sale: 3,333 shares Aggregate market value: $416,625.00 Class A shares outstanding: 42,644,388 shares

3 metrics

Class A shares proposed for sale 3,333 shares Notice lists a proposed sale on September 24, 2026

Aggregate market value $416,625.00 Proposed sale of Class A shares

Class A shares outstanding 42,644,388 shares Number listed in the securities information

Key Terms

Rule 144, Stock Option Exercise, attorney-in-fact

3 terms

Rule 144 regulatory

"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

"Stock Option Exercise"

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.

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.

How many BLLN shares does David Tsao propose to sell?

David Tsao’s notice lists 3,333 Class A shares for sale, with an aggregate market value of $416,625.00. Fidelity Brokerage Services LLC is listed in the securities information, and the sale date is September 24, 2026.

What prior BLLN share sales does David Tsao’s notice list?

The past-three-months table lists sales by David Tsao of 20,000 shares on July 13, 2026, 10,000 on August 10, 10,000 on August 25, and 20,000 on September 9. The trust entries list 3,500, 3,500, and 1,750 shares on July 13, August 10, and September 9, respectively; remarks identify Icontrust LLC as trustee.

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	3333	416625.00	42644388	09/24/2026	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	09/24/2026	Stock Option Exercise	Issuer			3333	09/24/2026	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	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
David Tsao 1035 OBrien Drive, Menlo Park CA 94025	Class A	09/09/2026	20000	1975400.00
Dt 2021 Irrevocable Trust 1035 OBrien Drive Menlo CA 94025	Class A	09/09/2026	1750	170695.00

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	09/24/2026
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/Wade Moss, 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)