What is x402?
x402 is an open payment protocol for HTTP. An API answers a request with 402 Payment Required and a price, the client signs a payment for exactly that amount, and the same request is sent again with the payment attached. The buyer needs no account, API key or subscription, so an AI agent can pay for one API call at a time.
| Item | Current state |
|---|---|
| x402 version vAPI pays | x402 v2, exact scheme |
| Payment asset | USDC, moved by a signed EIP-3009 authorization |
| Networks vAPI clients pay on | Base (eip155:8453) and Arc (eip155:5042); Arc Testnet (eip155:5042002) when enabled |
| vAPI Call | Launching. The console does not serve Call yet. |
| Checked on | 2026-10-02 |
How an x402 payment works
- The client sends the request with no payment header.
- The API answers
402 Payment Required. The offer names the scheme, network, USDC contract, amount, recipient (payTo) and a timeout. x402 v2 puts it in thePAYMENT-REQUIREDheader and in the response body. - The client checks the offer against its own limits and signs one EIP-3009 authorization for that amount and recipient.
- The client sends the same request again with the signed payment in the
PAYMENT-SIGNATUREheader. - The API, usually through a facilitator, verifies the signature and settles the transfer onchain.
- The API returns its response, with the settlement result in the
PAYMENT-RESPONSEheader.
The signature fixes the recipient, amount, token, chain, nonce and validity window, so nobody can change them after the buyer signs. The buyer pays no gas, because USDC moves by signed authorization and the settling party submits the transaction.
What a 402 response contains
vapi check in the vapi-network client reads an API's 402 and tests it against the x402 v2 rules without paying. This run checked vAPI's own paid endpoint on staging on 2026-10-02. The output is shown without its title line.
$ vapi check https://api-staging.vapinetwork.ai/x402/decode --method POST
pass status HTTP 402 Payment Required.
pass transport The offer is in the PAYMENT-REQUIRED header and the body.
pass version Declares x402 version 2.
pass fields Every field x402 v2 requires is present and well-typed.
pass scheme 1 of 1 accepted option uses the exact scheme.
pass asset Pays canonical USDC on eip155:8453.
pass pay_to Every exact option names a well-formed payTo address.
pass timeout maxTimeoutSeconds 120.
pass extensions Advertises bazaar, builder-code, payment-identifier.
pass discovery Discovery document at https://api-staging.vapinetwork.ai/.well-known/x402 lists 1 resource.
pass openapi https://api-staging.vapinetwork.ai/x402/openapi.json declares x-payment-info for POST /x402/decode.
11 passed, 0 warnings, 0 failed.What a facilitator does
A facilitator verifies a signed x402 payment against the API's offer and submits it onchain for the API. The API keeps control of its price and recipient. vAPI's paid decoder, POST /x402/decode, settles through a facilitator and never signs for a buyer.
Where vAPI Network fits
- vAPI Call is a directory of x402 APIs. Search and inspect are free, and each paid request goes from the buyer to the API's own payout address.
- vapi-network is the public client, published on npm under the Apache 2.0 license. It keeps the buyer's key on the buyer's machine, checks every live 402 against a per-call and a daily cap, and signs one exact USDC authorization per request.
- vAPI never signs for a buyer and holds no buyer balance.
- 5% network fee on self-listed APIs, nothing on indexed listings. The provider's onchain splitter takes the fee from what it receives, so buyers pay the quoted price.
x402 on Arc
Arc is Circle's layer 1 network, where USDC is also the gas token. vAPI clients pay exact USDC offers on Arc mainnet (eip155:5042), and on Arc Testnet (eip155:5042002) when that network is enabled.
Self-listing through a fee splitter is Base-only, because no splitter factory is deployed on Arc. A listing that quotes Arc pays the provider directly and carries no network fee.
Who maintains x402
Coinbase contributed the x402 protocol to the Linux Foundation. On 14 July 2026 the Linux Foundation announced the operational launch of the x402 Foundation, which stewards the protocol under open governance. The specification is public on GitHub.