What is x402?

x402 is an open payment standard that lets an autonomous agent pay for an API call in stablecoin (USDC) with no pre-existing account, using the HTTP 402 “Payment Required” response as the trigger.

How x402 works

x402 reuses an HTTP status code that was almost never used: 402 “Payment Required”. The flow has three steps. First, the agent requests a resource and the server answers with a 402 that describes the required payment (amount, currency, network, and where to pay). Second, the client pays on-chain in USDC — with no signup and no card — and obtains an on-chain proof of payment. Third, the agent retries the request attaching that proof, and the server returns the response. It all happens inside the HTTP exchange: no billing portal, no onboarding, no human in the loop.

Why it matters for AI agents

An AI agent that needs data or tools pays for hundreds or thousands of small calls. The classic model — create an account, store a card, manage keys — assumes a human behind it. x402 removes that assumption: payment is machine-to-machine, per call, with no account managed by a person. That lets an agent discover a new service and pay for it instantly, which is hard to do with subscriptions and API keys that require manual provisioning. It is an early standard; real-world adoption is still limited, so treat it as an emerging rail rather than the dominant one.

x402 vs API keys and subscriptions

With traditional API keys, someone creates an account, gets a secret, and manages it; billing is monthly or from a prepaid quota, and the provider trusts that credential. x402 flips the model: there is no account and no long-lived secret — payment travels with the request itself and settles on-chain per call. Keys are still practical for stable, high-volume relationships; x402 shines when the consumer is an ephemeral agent that wants to pay for exactly what it uses, with no signup friction. They are not mutually exclusive: a gateway can offer both.

How Obolo supports x402

Obolo is an MCP gateway and marketplace, and acts as merchant of record for the agent economy: your agent pays per tool call from a prepaid balance. x402 is one of its three payment rails, alongside Stripe and prepaid USDC balance. Obolo does not force x402 on you — it is an option, not a requirement. On any rail, Obolo keeps the same gateway guarantees: two verification tiers (crawled/verified), SSRF blocking, and manifest-hash drift detection, plus metering on every call. See how Obolo protects every call.

Frequently asked questions

Is x402 a blockchain?

No. x402 is a payment standard on top of HTTP, not a blockchain. It uses the 402 “Payment Required” code to negotiate payment and then settles on a network that supports USDC; the chain is the settlement medium, not the standard itself.

What currency does x402 use?

USDC, a dollar-pegged stablecoin. Paying in a stable value keeps the per-call amount predictable and avoids exposure to the volatility of a generic crypto asset.

Does Obolo require x402?

No. In Obolo, x402 is one of three payment rails alongside Stripe and prepaid USDC balance. You can use whichever you prefer; x402 is an option for machine-to-machine payments with no pre-existing account.