Company: BLLN
Filing Date: 2025-10-17
Form Type: S-1/A
Source: 0001193125-25-242632
Chunk: 315

Company: BillionToOne, Inc.
Filing Date: 2025-10-17
Form: S-1/A
Chunk 315
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 agent. The holder’s agent will then be required to provide certification to the applicable withholding
agent, either directly or through other intermediaries. Any such certifications provided to an applicable withholding agent or intermediary must be updated periodically. If you are eligible for a reduced rate of U.S. federal withholding tax under an
income tax treaty, you may generally obtain a refund or credit of any excess amounts withheld by filing an appropriate claim for a refund with the IRS in a timely manner.

Dividends received by a non-U.S. holder that are effectively connected with a U.S. trade or business conducted by the non-U.S. holder, and if required by an applicable income tax treaty between the United States and the

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non-U.S.holder’s country of residence, are attributable to a permanent establishment or fixed base maintained by the non-U.S.holder in the United States, are not subject to U.S. withholding tax. To obtain this exemption, a non-U.S.holder must provide the applicable withholding agent with an IRS Form W-8ECI(or any successor or substitute form thereof) properly certifying such exemption, and periodically update such certification. Such effectively connected dividends, although not subject to withholding tax, are taxed at the same U.S. federal income tax rates applicable to U.S. persons, net of certain deductions and credits. In addition to being taxed at U.S. federal income tax rates, dividends received by a corporate non-U.S.holder that are effectively connected with a U.S. trade or business of the corporate non-U.S.holder may also be subject to a branch profits tax at a rate of 30% or such lower rate as may be specified by an applicable tax treaty. Gain on sale or other disposition of Class A common stock Subject to the discussion below under the section titled “—Backup withholding and information reporting” and “—Foreign Account Tax Compliance Act,” non-U.S.holders will generally not be subject to U.S. federal income tax on any gains realized on the sale, exchange or other disposition of our Class A common stock unless:

| • |     | the gain (1) is effectively connected with the conduct by the non-U.S. holder                                                                                                               
 of a U.S. trade or business and (2) if required by an applicable income tax treaty between the United States and the non-U.S. holder’s country of residence, is attributable to a permanent 
 establishment or fixed base maintained by the non-U.S. holder in the United States (in which case the special rules described below