How do use x402 payments with my AI platform?

How a human uses AI Agent Payments with x402

"AI Agent Payments" is a product built on x402, an open standard for machine-to-machine payments. With x402 a service charges by returning HTTP 402 "Payment Required" with the exact USDC amount and accepted chains; the client signs a USDC payment and retries with it in a header; settlement happens on-chain only after the tool succeeds. There is no account and no API key — a wallet is the identity, and each request is paid in USDC.

The human's job is one-time setup, not approving every payment. A human:

1. Creates a wallet and funds it with USDC on the chain the service accepts (Base is primary; Polygon, Sei, Avalanche, Solana and Algorand are also supported).
2. Hands that wallet to the assistant — a private key in its secret store/config, or a connected x402-enabled tool/MCP server.
3. Optionally caps how much the assistant can spend.
4. Lets the assistant work. From then on, whenever the assistant hits a paid tool or endpoint, it pays automatically, one request at a time.

The payment step itself is the same regardless of which assistant drives it:

• The assistant requests the paid resource.
• The server replies HTTP 402 with the terms: asset (USDC contract address), payTo, amount in 6-decimal atomic units, scheme, network, and a validity window.
• The assistant signs the authorization — an EIP-3009 transferWithAuthorization on EVM chains — and retries the identical request with the signed payment in the X-PAYMENT header.
• The server verifies, runs the tool, and settles on-chain. A failed tool never consumes the payment.

Examples

• ChatGPT: a human connects a funded wallet to a custom GPT or an x402-enabled action/MCP server. When the GPT needs a paid resource mid-task (for example live market data), it calls the endpoint, receives the 402, signs, and pays per request — the human never approves each micro-payment by hand.
• Claude Code: a human puts the funded wallet's key in Claude Code's environment. While coding, Claude Code can call an x402-priced API and pay per call from that wallet, retrying with the signed X-PAYMENT header.
• Mistral: a human gives a Mistral assistant a funded wallet through its tool/MCP integration, so it pays per request for any x402-enabled service it invokes.
• Kimi: same pattern — a human funds a wallet and connects it to Kimi, which then pays USDC per request for external x402-priced tools using the same 402 → sign → retry flow.
• Open source AI agents: a human drops the open x402 client/SDK into any open-source agent (LangChain, Eliza, CrewAI, and similar), supplies a funded key, and the agent signs EIP-3009 authorizations and pays per request with no account and no API key.

Bottom line: the human funds a wallet and hands it to the assistant once; after that the assistant pays on its own, request by request, and settlement is on-chain USDC.