Company: BLLN
Filing Date: 2025-10-17
Form Type: S-1/A
Source: 0001193125-25-242632
Chunk: 1

Company: BillionToOne, Inc.
Filing Date: 2025-10-17
Form: S-1/A
Chunk 1
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, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐ If this form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐ If this form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ☐ Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-acceleratedfiler, a smaller reporting company or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company” and “emerging growth company” in Rule 12b-2of the Exchange Act.

| Large accelerated filer |     | ☐ |     | Accelerated filer         |     | ☐ |
| Non-accelerated filer   |     | ☒ |     | Smaller reporting company |     | ☐ |
|                         |     |   |     | Emerging growth company   |     | ☒ |

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ☐ This registration statement shall hereafter become effective in accordance with the provisions of Section 8(a) of the Securities Act of 1933.

The information in this prospectus is not complete and may be changed. We may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted. Subject to Completion, dated October 17, 2025 Preliminary prospectus 3,846,000 shares Class A common stock This is an initial public offering of shares of Class A common stock of BillionToOne, Inc. We are offering 3,846,000 shares of our Class A common stock to be sold in this offering. The initial public offering price is expected to be between $49.00 and $55.00 per share. Prior to this