How do AI agents pay for an API?
An AI agent pays when a server sends a 402 challenge. It signs the exact request, retries, and the PAYMENT-RESPONSE header is its receipt.
The steps, in order
The agent asks for a page or a data call. The server replies with HTTP 402 instead of data. The 402 header lists price, currency, and network.
Here the price is 0.001 USDC per accepted read. The network is Base, chain eip155:8453. The protocol is x402 version 2.
The agent signs a payment for that exact amount. It sends the same request again with proof attached. A facilitator checks the payment and settles it on Base. The server then returns the data it promised. The reply carries a PAYMENT-RESPONSE header as the receipt.
One real job, with real numbers
ScriptMasterLabs has published settlement observations since September 2, 2026. Those records counted 96 settlements on Base through October 6, 2026. Most early settlements were owner self-tests, not customer sales.
A live probe found a 402 reply in 0.67 seconds. That reply quoted 0.001 USDC for one read. Failed reads cost nothing under those terms.
What the 402 is not
The 402 is the price tag, not the receipt. No money has moved when 402 first appears. Money moves only after signing and settlement succeed. The PAYMENT-RESPONSE header is the receipt after settlement.
We tested that line directly on the 402 proof question.
What an agent needs first
An agent needs a wallet with USDC on Base. It needs code that reads x402 v2 challenges. It needs a spending cap set before work starts. No account or API key is needed here. No human checkout step sits in the loop.
See one live example
One live example makes the steps concrete. You can see the live reader and its price before any agent pays.
Common questions
Is a 402 challenge proof of payment? No. The 402 is the price tag, not the receipt.
How much does one read cost here? One accepted read costs 0.001 USDC on Base. Failed reads cost nothing.
What currency and network are used? Payments use USDC on Base, chain eip155:8453.