What is x402?

x402 is a way for software — mostly AI agents — to pay for things over the web without a human clicking 'confirm' each time. The name comes from HTTP status code 402, 'Payment Required,' which was reserved back in 1997 and then sat unused for nearly thirty years. x402 finally uses it: when an agent requests something that costs money, the server answers 402 with a price and a payment address, the agent pays in a stablecoin (usually USDC on the Base network), attaches the receipt, and gets the resource. That's the whole loop — request, price, pay, receive — at web speed, for fees under a cent. Coinbase built it, then handed it to the Linux Foundation in April 2026 so no single company owns it. It matters because agents can't use credit card checkout pages, and x402 gives them a payment method that works the way they do: programmatic, instant, no account signup.