Why agent payments are different
Traditional payments were built for people. Credit cards require a cardholder; bank accounts need KYC; subscriptions assume a human reviews the invoice. None of that fits software that wants to buy a single API call at 3am. The hard requirements for agent payments are:
Sub-cent micropayments
Agents need to pay $0.001 per call — impossible under a card processor’s ~$0.30 floor. x402 has no minimum.
No human in the loop
Agents transact 24/7. There is nobody to approve a charge or review an invoice, so payment must be programmatic.
Instant settlement
A synchronous API call can’t wait three business days. On Base, settlement is ~2 seconds.
Verifiable, no chargebacks
Every payment is on-chain proof. No disputes or fraud reversals to reconcile later.
The combination of the x402 protocol and USDC on Base satisfies all four natively, which is why it has become the default rail for agentic payments.
How an agent pays, step by step
- Request. The agent makes a normal HTTP request to an x402-enabled endpoint.
- 402 challenge. The server replies with HTTP 402 and JSON payment requirements (amount, USDC, Base, recipient).
- Sign payment. The agent’s wallet (e.g. Coinbase AgentKit or any x402 client) signs the on-chain transfer.
- Retry with proof. The agent repeats the request carrying an
X-PAYMENTheader with the receipt. - Verify & respond. The server verifies in milliseconds and returns the data. No human involved.
You can generate a sample challenge and copy client/server code with the free 402 response builder, and compute exact amounts with the base-unit converter.
Related building blocks
Frequently asked questions
What are AI agent payments?
AI agent payments are autonomous, machine-to-machine transactions executed by software agents without a human approving each one. Using protocols like x402 (HTTP 402 Payment Required) with USDC on Base, an agent can pay for APIs, compute and data programmatically, settling micropayments as small as a fraction of a cent in real time.
Which protocol is best for AI agent payments?
The x402 protocol, originally proposed by Coinbase, is the leading open standard. It uses USDC on Base for sub-cent fees, settles in about two seconds, and needs no human approval. mpp.best tracks 1211 open-source projects implementing it.
How do AI agents pay for API calls?
With x402: the API returns an HTTP 402 response with payment details (amount, token, network). The agent pays USDC on Base and retries the request with cryptographic proof. The whole loop takes roughly two seconds and requires no human interaction.
What is an AI agent wallet?
An AI agent wallet is a programmable crypto wallet the agent controls autonomously. It holds USDC, signs transactions and pays for services without human approval. Tools like Coinbase AgentKit provide agent wallets that integrate with x402 and MCP.
Explore the ecosystem: browse 1211 x402 projects among 1600+ tracked tools, compare payment protocols, or submit your project.