Form 4 Filing for Thomas P. Lynch

Thomas P. Lynch, an officer of BillionToOne, Inc., reported a transaction on October 13, 2026. He acquired 2,000 shares of Class A Common Stock at a price of $8.65 per share, increasing his post-transaction holdings to 10,700 shares. Additionally, Lynch exercised a stock option for 2,000 shares of Class A Common Stock, also at an exercise price of $8.65 per share. This exercise resulted in him holding 38,974 shares of stock options. The options were fully vested and exercisable, as previously reported. The transactions were made under a general arrangement, and Lynch holds a direct ownership of these securities.