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x402
also x402 protocol or x402 payments or HTTP 402 payments
Definition of x402
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: an open payment protocol that uses the HTTP 402 Payment Required status code to let software clients, especially AI agents, automatically pay for APIs, data, content, or computing services as part of a web request
- The research agent used x402 to pay a few cents for a specialized database query without creating an account.
- The inference endpoint returned an x402 payment request before serving the model call.
Origin & history
Coinbase introduced x402 in May 2025 as an open standard for internet-native payments. Its name comes from HTTP status code 402, Payment Required, which had long existed without a widely adopted payment mechanism. The protocol gained attention as AI agents began needing machine-readable ways to buy data, API calls, model inference, and other digital services without a person completing a checkout form.
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Cite this entry
"X402." AI Dictionary, Dadgogo, https://dadgogo.com/dictionary/x402/. Accessed 9 Oct. 2026.