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Nevermined Pay is Live

AI agents on real credit card rails

Details

Glossary

What is x402?

x402 is an open HTTP standard for AI agent payments. When an agent hits a paywall, the server responds with 402 Payment Required. The agent attaches a payment credential in the next request header, and the purchase completes in milliseconds. No checkout, no redirect, no human in the loop.

Where the name comes from

HTTP 402 has been reserved in the spec since the 1990s with the comment “Payment Required.” For decades it was unused — there was no payment standard to hang off it. x402 is the protocol that finally fills that slot. The “x” signals that it's a community-defined extension over the bare HTTP status, not a single vendor's proprietary scheme.

The handshake

Three messages, two parties. The agent is the buyer; the server hosting the resource is the seller.

  1. The agent issues a normal HTTP request to a paywalled endpoint.
  2. The server responds 402 Payment Required with a body describing the price, the accepted payment rails, and a nonce. No auth dance, no cookie, no redirect.
  3. The agent re-issues the same request with a payment-signature header carrying a signed payment authorization. The server verifies, settles, and returns the resource.

End-to-end, this is typically under 200 ms — fast enough to sit in the inner loop of an agent workflow without breaking user perception of latency.

What x402 is good for

  • Pay-per-call APIs. Sub-cent metering on data, tools, or compute that an agent consumes a request at a time.
  • Crawler monetization. Publishers can charge AI training and retrieval crawlers per page without negotiating one-off deals. See how it works for content owners.
  • MCP tool calls. When an MCP server exposes a paid tool, x402 is the rail the LLM uses to authorize the call without asking the user mid-conversation.
  • Agent-to-agent commerce. Two autonomous agents negotiating price for a service can settle via x402 in the same request that contains the work.

What x402 isn't

x402 is the handshake, not the wallet, not the settlement rail, and not the dispute system. It says “here is a signed authorization for this much, on this rail” — it doesn't care whether the rail underneath is a Visa virtual card, USDC, a Stripe charge, or off-chain credits. Most production deployments compose x402 with a facilitator that handles the actual money movement; that's where Nevermined fits.

Where Nevermined fits

Nevermined operates the Nevermined x402 Facilitator: the coordinating service that verifies payment headers, settles across rails (Stripe, USDC, Visa virtual cards), and exposes the metering primitives so sellers can attribute every successful call to the right wallet. The Nevermined SDKs (TypeScript, Python, CLI) wrap the protocol so an agent or seller doesn't need to implement the byte-level spec themselves.

For platforms that want to monetize AI traffic without committing to one settlement rail, the x402 + facilitator combination means future-proofing: whichever rail wins, the agent code stays the same.

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