Form 4 Filing for BillionToOne, Inc.

Sakakibara Shan Riku, Chief Product Officer of BillionToOne, Inc., reported a transaction on September 10, 2026. The transaction involved the disposal of 3500 shares of Class A Common Stock. The disposal code was "D", indicating a sale or other disposition. The transaction price was $0.00 per share. Following this transaction, Sakakibara Shan Riku holds 196,500 shares of Class A Common Stock. The filing was signed by Thomas P. Lynch, Attorney-in-Fact, on September 14, 2026.