Thomas P. Lynch - 17 Sep 2026 Form 4 Insider Report for BillionToOne, Inc. (BLLN)

Reporting relationship: General Counsel, Chief Compliance Officer and Secretary
Issuer ticker: BLLN
Reported as of: 17 Sep 2026
Net transaction value: -$3,873,966
SEC form: 4
Accepted by SEC: 21 Sep 2026, 19:00:11 UTC
Prior SEC filing: 10 Sep 2026
Source filing: View source filing
Reporting owner signature: Thomas P. Lynch

Key filing fact

Thomas P. Lynch filed Form 4 for BillionToOne, Inc. (BLLN) on 21 Sep 2026.

Key facts

This page summarizes Thomas P. Lynch's Form 4 filing for BillionToOne, Inc. (BLLN).
12 reported transactions and 4 derivative rows are listed below.
Accepted by SEC: 21 Sep 2026, 19:00.

Change

Previous filing in this sequence was filed on 10 Sep 2026.
Current net transaction value: -$3,873,966.

Research use

This tells you what this filing adds before you inspect full transaction and derivative tables.
You can trace every row back to the original SEC filing document.

Evidence

Filed on Form 4

Ownership activity is grounded in SEC Form 4 disclosures.

View source filing

Reporting Owners (1)

CIK 0001659824 Primary reporting owner

Lynch Thomas P.

Relationship: General Counsel, Chief Compliance Officer and Secretary
Address: C/O BILLIONTOONE, INC., 1035 O'BRIEN DRIVE, MENLO PARK
Signature: Thomas P. Lynch
Signature date: 21 Sep 2026

Reported non-derivative transactions

Shares, units, or other non-derivative securities reported in this filing.

BLLN transaction

Class A Common Stock

Options Exercise

Transaction value
Shares: +19,384
Change %: +2769%
Price: $8.65^*
Shares after: 20,084
Date: 17 Sep 2026
Ownership: Direct
Footnotes: F1

BLLN transaction

Class A Common Stock

Options Exercise

Transaction value
Shares: +6,968
Change %: +35%
Price: $11.55^*
Shares after: 27,052
Date: 17 Sep 2026
Ownership: Direct
Footnotes: F1

BLLN transaction

Class A Common Stock

Options Exercise

Transaction value
Shares: +2,920
Change %: +11%
Price: $17.12^*
Shares after: 29,972
Date: 17 Sep 2026
Ownership: Direct
Footnotes: F1

BLLN transaction

Class A Common Stock

Options Exercise

Transaction value
Shares: +5,840
Change %: +19%
Price: $30.78^*
Shares after: 35,812
Date: 17 Sep 2026
Ownership: Direct
Footnotes: F1

BLLN transaction

Class A Common Stock

Sale

Transaction value: $2,139,193
Shares: -19,384
Change %: -54%
Price: $110.36
Shares after: 16,428
Date: 17 Sep 2026
Ownership: Direct
Footnotes: F1, F2

BLLN transaction

Class A Common Stock

Sale

Transaction value: $768,561
Shares: -6,968
Change %: -42%
Price: $110.30
Shares after: 9,460
Date: 17 Sep 2026
Ownership: Direct
Footnotes: F1, F3

BLLN transaction

Class A Common Stock

Sale

Transaction value: $322,100
Shares: -2,920
Change %: -31%
Price: $110.31
Shares after: 6,540
Date: 17 Sep 2026
Ownership: Direct
Footnotes: F1, F3

BLLN transaction

Class A Common Stock

Sale

Transaction value: $644,112
Shares: -5,840
Change %: -89%
Price: $110.29
Shares after: 700
Date: 17 Sep 2026
Ownership: Direct
Footnotes: F1, F2

Reported derivative securities

Options, warrants, convertible securities, or similar derivative positions disclosed in the filing.

BLLN transaction Derivative

Stock Option (right to buy)

Options Exercise

Transaction value
Shares: -19,384
Change %: -28%
Price: $8.65^*
Shares after: 48,974
Date: 17 Sep 2026
Ownership: Direct
Underlying class: Class A Common Stock
Underlying amount: 19,384
Exercise price: $8.65
Footnotes: F4

BLLN transaction Derivative

Stock Option (right to buy)

Options Exercise

Transaction value
Shares: -6,968
Change %: -63%
Price: $11.55^*
Shares after: 4,063
Date: 17 Sep 2026
Ownership: Direct
Underlying class: Class A Common Stock
Underlying amount: 6,968
Exercise price: $11.55
Footnotes: F4

BLLN transaction Derivative

Stock Option (right to buy)

Options Exercise

Transaction value
Shares: -2,920
Change %: -35%
Price: $17.12^*
Shares after: 5,417
Date: 17 Sep 2026
Ownership: Direct
Underlying class: Class A Common Stock
Underlying amount: 2,920
Exercise price: $17.12
Footnotes: F4

BLLN transaction Derivative

Stock Option (right to buy)

Options Exercise

Transaction value
Shares: -5,840
Change %: -16%
Price: $30.78^*
Shares after: 30,834
Date: 17 Sep 2026
Ownership: Direct
Underlying class: Class A Common Stock
Underlying amount: 5,840
Exercise price: $30.78
Footnotes: F4

^* marks a reported price that did not pass the local price check.

Additional SEC filing notes

Filing notes and footnotes

Rule 10b5-1 trading plan

These transactions were reported as open-market trades under a Rule 10b5-1 plan. The plan lets an insider set trading instructions in advance, which can reduce the risk of trading while in possession of material nonpublic information.

Original filing language: transaction made pursuant to a contract, instruction, or written plan intended to satisfy Rule 10b5-1(c).

Explanation of responses 4 footnotes

Footnote 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.

Footnote 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.

Footnote 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.

Footnote 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.

SEC remarks

General Counsel, Chief Compliance Officer and Secretary