X402 native payments for AI Agents.
x402 turns HTTP 402, a status code defined in HTTP/1.1 (RFC 2616) and left unused for over 20 years, into a payment protocol machines can read. Your agent hits an API, gets a 402 with payment terms, signs a gasless USDC transfer, retries, and the resource unlocks. No checkout pages, no API keys, no monthly bills.
A status code that waited two decades.
HTTP 402 Payment Required has been in the spec since HTTP/1.1 (RFC 2068, 1997; RFC 2616, 1999) but sat 'reserved for future use' for over 20 years. x402 finally gives it teeth: when a server returns 402, it includes a payment-required header describing accepted tokens, amounts and networks. The client signs a token transfer off-chain, attaches it as a payment-signature header, and replays the request. The server verifies, settles, and serves the resource. No redirects, no iframes, no third-party SDKs.
The x402 handshake
- 01GET /api/resource
- 02402 + payment-required
- 03Sign EIP-3009 / Permit2
- 04Retry + payment-signature
- 05200 OK + payment-response
Two ways to sign. You pick.
The 402 Payment Required header names the token, the amount, and the network. BlockVault settles it two ways: EIP-3009 for gasless USDC, or Permit2 for any ERC-20. It picks the best one automatically, and you can always override.
EIP-3009 (gasless USDC)
Uses `transferWithAuthorization` built into the USDC contract. Zero gas for the payer. Supported on Ethereum, Polygon, Base, Arbitrum, Optimism and BSC.
- Gas cost: zero (meta-tx)
- Tokens: USDC only
- Chains: 6 EVM networks
Permit2 (universal ERC-20)
Uses Uniswap's Permit2 router for any ERC-20 with a one-time allowance. Requires gas for the settlement transaction.
- Gas cost: ~60k gas (settlement tx)
- Tokens: any ERC-20
- Chains: 6 EVM networks
In practice: if you're paying USDC on a supported chain, it's gasless. For everything else, Permit2 kicks in and gas is minimal.
A 402 that actually works, two decades later.
HTTP 402 was defined in HTTP/1.1 (RFC 2068, 1997; RFC 2616, 1999) and sat unused for over 20 years. BlockVault is the first wallet to implement on-device AI and native x402 payments. A drop-in called x402Fetch intercepts 402 responses, parses the payment header, queues your approval, builds the signature, and retries. You see one confirmation. The server sees a paid request.
Production endpoint
402.blockvault.ai
402.blockvault.ai is a live x402 server that sells GPU inference (Gemma 4, Llama) per token via USDC on Base.
See how BlockVault stacks up.
← scroll →
| BlockVault | Coinbase x402 | MetaMask | Trust Wallet | Phantom | Binance | |
|---|---|---|---|---|---|---|
| x402 native | ✓ | ✓ | — | — | — | — |
| Gasless (EIP-3009) | ✓ | — | — | — | — | — |
| Multi-chain (6+ EVM) | ✓ | ✓ | ✓ | ✓ | ~ | ✓ |
| AI on-device | ✓ | — | — | — | — | — |
| Self-custody | ✓ | ✓ | ✓ | ✓ | ✓ | — |
| Mobile-first | ✓ | ✓ | ~ | ✓ | ✓ | ✓ |
The agentic payment standard.
After more than two decades reserved, HTTP 402 finally has a job. AI agents need autonomous payment for APIs, GPU compute, and premium data feeds. x402 gives them a native HTTP rail: the agent receives a 402, signs a USDC transfer, retries. No checkout pages, no subscriptions, no human in the loop.
The x402 reference library.
Everything you need to understand, implement and deploy HTTP 402, the status code defined in HTTP/1.1 and left unused for over 20 years. From the raw spec to a production case study.
Questions about a 20-year-old status code.
Is x402 a blockchain or a token?
Neither. x402 is an HTTP protocol that uses existing blockchains (Ethereum, Base, Polygon, etc.) for settlement. No new chain, no new token.Do I need ETH for gas to make an x402 payment?
Not with EIP-3009. USDC transfers via transferWithAuthorization are gasless for the sender. The facilitator (server) pays gas.Can my AI agent spend without my approval?
Only within the policies you set. BlockVault enforces per-domain caps, daily limits and token allow-lists locally before any signature is released.Which tokens work with x402?
USDC on 6 EVM chains via EIP-3009 (gasless). Any ERC-20 via Permit2 (requires gas). Most x402 servers accept USDC.How fast is an x402 payment?
One off-chain signature + one HTTP retry. With EIP-3009 there is no on-chain transaction from the payer, so settlement is as fast as the facilitator confirms (~1-3 seconds).Is x402 open source?
Yes. The protocol is defined at x402-foundation/x402 on GitHub. Anyone can implement a client or server.Can I build an x402-protected API?
Yes. Return HTTP 402 with a payment-required header containing your terms (token, amount, network, receiver). Any x402-compatible wallet can pay.What is an agentic payment?
An agentic payment is a transaction an AI agent initiates and completes without human intervention. The agent detects a paywall (HTTP 402), evaluates the cost against its spend policy, signs a transfer, and settles. All within the same HTTP request cycle.How does x402 enable agentic payments?
x402 encodes payment terms in HTTP headers. When an agent gets a 402, it reads the payment-required header (token, amount, network, receiver), signs a gasless USDC transfer via EIP-3009, attaches the signature, and replays the request. No redirects, no OAuth, no human approval for pre-authorized amounts.Are agentic payments safe without human approval?
Yes. BlockVault enforces spend policies locally: per-request caps, daily limits, and domain allowlists. The agent can only spend within bounds you set. Any payment exceeding the policy triggers a Human-In-The-Loop (HITL) approval modal before signing.Where did HTTP 402 come from?
402 Payment Required was first defined in HTTP/1.1 in RFC 2068 (1997), carried through RFC 2616 (1999), and kept 'reserved' in RFC 7231 (2014). For more than two decades it sat unused. x402 is the first protocol to define real payment semantics for it, which is why you now see working 402 payments in the wild.
Ready when you are.
Install BlockVault, connect your wallet, and let the agent pay APIs and GPU time over x402. First payment takes seconds.