W-9 vs W-8BEN for AI training work: which tax form you fill in

One question decides it

Most AI training platforms ask for a tax form during onboarding, before any money moves. Which one you fill in, a W-9 or a W-8BEN, comes down to a single question: does the IRS treat you as a US person?

The Form W-8BEN instructions define a US person as including "an individual who is a citizen or resident of the United States". They are explicit on the case people get wrong: if you are a US citizen, you do not use Form W-8BEN "even if you reside outside the United States". You use Form W-9 instead.

Form W-9: for US persons

The IRS page About Form W-9 describes its job in one line: you use it "to provide your correct Taxpayer Identification Number (TIN) to the person who is required to file an information return with the IRS", for example to report income paid to you.

The platform uses it for year-end reporting, covered in 1099-NEC vs 1042-S.

Form W-8BEN: for everyone else

The IRS page About Form W-8BEN says you give the form "to the withholding agent or payer if you are a foreign person and you are the beneficial owner of an amount subject to withholding", and that you submit it when asked "whether or not you are claiming a reduced rate of, or exemption from, withholding".

According to the instructions, the form does three things: it establishes that you are not a US person, that you are the beneficial owner of the income, and, if applicable, it claims a reduced rate or exemption under an income tax treaty.

The form goes to whoever asked for it, not to the IRS. The instructions say plainly: "Do not send Form W-8BEN to the IRS."

What the W-8BEN asks for, at a high level

Following the line-by-line instructions:

1. Part I, identity. Your name, country of citizenship, and permanent residence address in the country where you are resident for income tax (not a post office box).
2. Tax numbers. A US SSN or ITIN on line 5 if you have one, or a foreign tax identification number on line 6a. The instructions say that to claim certain treaty benefits you must complete one or the other.
3. Part II, treaty claim. Only if you are claiming treaty benefits: the country where you are resident for treaty purposes. US tax treaties and AI training income covers how that works.
4. Part III, certification. Your signature. The instructions say a withholding agent may allow you to provide the form with an electronic signature.

Two edge cases the instructions name

• Services performed in the United States. A nonresident claiming exemption from withholding on pay for personal services performed in the US uses Form 8233 or Form W-4 instead, not the W-8BEN.
• How long it lasts. A W-8BEN generally stays in effect until the last day of the third calendar year after the year you sign it, unless your circumstances change. If they do (you move, for example), the instructions say you must tell the withholding agent.

What the platforms say

Mercor's contractor documentation, summarised in how you actually get paid, states that EU-based contractors complete a W-8BEN during onboarding. Invisible Technologies asks for tax details during onboarding. Most platforms behind our listings do not publish which form they collect.

Everything here describes how the IRS explains these rules; it is not tax advice. Check your own situation with a tax professional who knows both US rules and those of the country you live in.

Labeling Jobs does not give financial or tax advice.