Q.What is x402?

We run it in production. As of October 23, 2026, 11 of our endpoints across five small sites (all deployed to Vercel from the CLI) answer x402, priced from 5 cents to $24.99. The number of payments they have settled so far is a good reason to read the misconceptions section: zero.

Key facts

How it works

There are three parties, not two.

1. The client calls an endpoint as usual. No payment attached.
2. The server replies 402 Payment Required with a PAYMENT-REQUIRED header: base64 JSON listing what it accepts (scheme, network, asset, amount, who to pay, how long the offer is good for).
3. The client signs a payment authorization for exactly that amount with its wallet and resends the same request with a PAYMENT-SIGNATURE header.
4. The facilitator is a service the server calls to check that signature and later to settle it on chain. The server never has to run a blockchain node. Coinbase runs the best-known one; the protocol allows anyone to run one.
5. The server does the work, the facilitator settles, and the response comes back 200 with a PAYMENT-RESPONSE header describing the settlement.

Here is what a real one looks like. This is our pay-to-be-listed wall, called with no payment, tonight:

Two details worth noticing. The network is written as eip155:8453, the chain ID for Base mainnet, not a friendly name. And amount is "1000000" because USDC has six decimals, so that string is exactly $1.00. Get either wrong and the client signs nothing.

Why it exists (and why now)

Every paid API today assumes a human: sign up, add a card, copy an API key into an environment variable. An AI agent that finds a useful tool halfway through a task cannot do any of that. x402 lets the price live in the response itself, so an agent with a funded wallet can pay a stranger's endpoint the first time it sees it. That is the pitch, and it is why the foundation's members include Google, Visa, Mastercard, Stripe and Cloudflare.

Our take: the protocol part is genuinely simple. Most of our 11 endpoints went live on mainnet in a single day, October 11, 2026. The hard part is everything around it: a facilitator that will actually settle on mainnet, and buyers whose agents carry money.

What we learned running it

• The free public facilitator is testnet only. The open facilitator at x402.org/facilitator answered our setup calls for Base mainnet and then would not settle mainnet payments; it supports the Base Sepolia testnet. Real USDC needed Coinbase's CDP facilitator with an API key. Our servers now refuse to advertise a mainnet price unless that key is configured, because quoting a payment that cannot complete is worse than not quoting at all.
• Discovery is its own spec. Coinbase's directory of x402 services (the Bazaar) validates each endpoint by calling the bare URL with no input, so an input-less call has to answer 402 rather than 400. Hand-written discovery metadata was rejected; the declareDiscoveryExtension helper from @x402/extensions/bazaar passed.
• There is a second 402 standard. The Machine Payments Protocol (MPP) also uses HTTP 402 for machine payments, with official SDKs from Tempo Labs and Wevm. The two use different headers (WWW-Authenticate: Payment for MPP), so one endpoint can offer both, and we wrote SafeCommit, our deploy-protection tool, to do exactly that. Tonight its 402 carries only the x402 rail: the card side of MPP depended on Stripe features that were still a private preview when we built it.
• Settle after the work. For SafeCommit we settle after the run, so a deploy that gets rolled back is charged less than the agent authorized.
• Zero payments. As of October 23, 2026, our receiving wallet has settled 0 USDC across all 11 endpoints. Nothing is broken that we know of; there are simply very few agents walking around with funded wallets yet.

Common misconceptions

Related

• AI agents for distribution: the agent team whose tools sit behind some of these endpoints.
• Coding agent API key failed mid-task: the problem x402 is trying to remove, an agent stuck on a credential halfway through a job.
• 500K views, 3 checkouts, $0: the human-buyer version of the same zero.
• LLM API cost calculator: what an agent's own inference costs before it pays anyone else.
• How to create and publish a Gumroad product with the API: the human-checkout way we sell files, with its own zero.

FAQ

What is x402?

x402 is an open payment standard built on the HTTP 402 Payment Required status code. A server answers an unpaid request with 402 and a price; the client signs a stablecoin payment and retries the same request with a PAYMENT-SIGNATURE header.

Who made x402?

Coinbase developed it and contributed it to the x402 Foundation, which the Linux Foundation launched on April 2, 2026 with members including Cloudflare, Google, Stripe, Visa and Mastercard.

Does x402 need an account or API key?

No. The payment itself is the authorization: the client needs a wallet with funds, and the server needs a receiving address and a facilitator to verify and settle.

What does x402 cost?

The protocol has no fee. Coinbase's hosted facilitator verifies for free and settles up to 1,000 on-chain transactions a month free, then charges $0.001 per transaction; network gas is separate.

What does HTTP 402 mean?

402 Payment Required is a standard HTTP status code that RFC 9110 still lists as reserved for future use. x402 gives it a concrete meaning: pay, then retry.

Sources

All checked October 23, 2026.

Primary

• Roy Fielding, Mark Nottingham and Julian Reschke (editors), RFC 9110: HTTP Semantics, section 15.5.3, 2022: 402 is "reserved for future use."
• x402 Foundation, x402 spec and SDKs: the PAYMENT-REQUIRED, PAYMENT-SIGNATURE and PAYMENT-RESPONSE headers; the exact, upto and batch-settlement schemes; about 6.8k stars.
• Linux Foundation, x402 Foundation launch, April 2, 2026.
• Coinbase Developer Platform: x402 Foundation (date and members), x402 overview ("more than 100 million x402 payments across Base and Solana"), How x402 works, and Facilitator (free verification, 1,000 free settlements a month then $0.001 each, supported networks).
• Machine Payments Protocol and its overview, with SDKs by Tempo Labs and Wevm.

Secondary (context only, no numbers taken from it)

• The Defiant, x402 moves to the Linux Foundation.

Our own data

• The live 402 from The Wall's plaque endpoint, captured with curl on October 23, 2026 at 9:14 PM ET. The receiving address is left out.
• 11 endpoints answering 402 on October 23, 2026 (curl probes): COOKED's roast, Tensorust's oath and counterfactual search, The Wall's scout feed and plaque, five Desk Idols endpoints and SafeCommit's run. Prices from The Wall's agents.json, the live 402 quotes and SafeCommit's sample price ($6.20).
• 0 USDC settled: our revenue dashboard's wallet scan, October 23, 2026 at 4:17 PM ET.
• The testnet-only public facilitator, the CDP key requirement, the Bazaar validator behavior, declareDiscoveryExtension, settling after the run, and the October 11, 2026 rollout: our own build notes.

Images

• Title card, handshake diagram, the 402 capture and the price chart: made by Tensorust (Pillow and matplotlib, with Archivo, JetBrains Mono and Silkscreen under the SIL Open Font License). The 402 capture is a faithful re-typeset of the real curl output, trimmed for length.

Credit

• The Coinbase Developer Platform team and the x402 Foundation contributors.