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x402 · AI agent payment protocol reviving HTTP 402 (overview)

Confidence: Likely Updated 2026-05-26 Review by 2026-09-22 Sources 1 Machine-translated Original (JA)
#agent-economy#payment#x402#coinbase#usdc#base
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This entry sits under AI agent payment protocols overview · seven-protocol landscape. Read it against Coinbase CDP · developer platform · AI agent on-chain wallet infrastructure for peer / contrast context and payments index for the broader system / regulatory boundary.

Key facts

  • Coinbase announced x402 in 2025-05 as an open-source protocol, reviving HTTP 402 after it had remained unused since its 1996 definition.
  • Default settlement uses USDC on Base, with support for Solana and other L2 networks.
  • The settlement layer is protocol-agnostic; applications can switch among Solana USDC, Tron USDT, or any EVM L2.
  • Facilitator model: the server delegates payment verification to a facilitator such as Coinbase.
  • Supports hot wallets and ERC-4337 smart-contract wallets; agents can use arbitrary wallet implementations.
  • USDC on Base settlement is under 2 seconds; the facilitator model is under 100 ms.
  • Single-call gas cost is under $0.001 on Base L2 with an ERC-4337 paymaster.
  • x402 Bazaar MCP catalogs more than 10,000 endpoints.

Mechanism / How it works

The AI agent economy is structurally mismatched with SaaS subscription flows. An agent may call hundreds of APIs on a transient basis, and it cannot complete a separate registration, card entry, subscription, and API-key-management flow for every API. The required primitive is per-call micropayment plus immediate authorization without account registration. x402 protocol flow: (1) the client requests an API endpoint; (2) the server returns HTTP 402 Payment Required plus an X-Payment-Required header containing amount, recipient, and accepted assets; (3) the client constructs a USDC transfer; (4) the client resends the request with an X-Payment header containing the transaction hash or proof; (5) the server verifies payment and returns the data. The facilitator model means the server does not need to verify on-chain transactions itself: by delegating to a facilitator such as Coinbase or Cloudflare, it reduces implementation burden and shortens verification to under 100 ms. Agent wallets are typically based on ERC-4337 or ERC-7702, with UserOps processed by a bundler.

Origin & evolution

RFC 7231 defined HTTP 402 Payment Required but left it as “reserved for future use,” and it remained practically unused for three decades. The missing component was a universal payment rail. USDC and stablecoins address that gap; for the surrounding strategy space, see chain × token × strategy trilemma. In 2025-05, Coinbase open-sourced x402 as a specification at github.com/coinbase/x402 and bound the default implementation to USDC on Base. Early 2025 H2 adopters included experimental implementations in Vercel AI SDK and Cloudflare Workers. In 2026-Q1, Cloudflare integrated x402 into the Workers production environment, meaning that more than 20% of global HTTP traffic had a default payment rail available. AWS API Gateway followed in 2026-Q2. x402 Bazaar MCP catalogs more than 10,000 endpoints as an agent-discoverable paid API directory.

Sources