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API Economy
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Owner: Coinbase + Cloudflare (open spec)

x402 · HTTP 402 Payment Required

Native HTTP payments for APIs and AI agents.

x402 revives the dormant HTTP 402 status code as a programmable payment handshake. APIs respond with 402 + payment requirements; clients (humans or AI agents) settle on-chain in stablecoins and retry the request. No accounts, no API keys, no card processors. Settlement on Base mainnet in under 200ms.

x402
What it does

The four things x402 actually delivers.

  • Reuses HTTP 402 as a programmable payment status code.
  • Embeds payment requirements directly in the HTTP response.
  • Settles in stablecoins (USDC) on EVM chains in <200ms.
  • No accounts, no API keys, no card processors — pure HTTP + crypto.
How it works

The flow, end to end.

1
Agent calls API

Standard HTTP request to a paid endpoint.

2
Server returns 402

Response carries price, network, payee, asset (USDC).

3
Agent signs & pays

EIP-3009 transferWithAuthorization signed by the wallet.

4
Facilitator settles

On-chain transfer verified by an x402 facilitator.

5
API replays the call

Original request returns the data with proof-of-payment.

Explained simply

A vending machine. You press B4 for chips. The screen shows $1.00. You insert a dollar. Chips drop immediately. That is x402: instant pay, instant access — at the protocol layer of the web.

xpay
Run an x402 facilitator without infra work

xpay operates an open, zero-fee facilitator at facilitator.xpay.sh on Base mainnet + Sepolia. Plug it into your API or your agent and inherit settlement, retries, and audit logs.

See xpay Facilitator →
Gap analysis

What x402 ships, what it does not, and what bridges the gap.

Has

Instant micropayments, open spec, multi-chain.

Missing

No native spending controls, no audit trail, no per-agent governance.

Bridge

Policy enforcement before payment executes — budget caps, category checks, recipient allowlists, signed receipts.

xpay
Spending guardrails for x402 agents

Smart Proxy sits between an agent and any x402 endpoint. It enforces per-agent budgets, daily caps, and merchant allowlists before the 402 settlement fires.

Smart Proxy →
vs the field

x402 compared.

x402 vs MPP

x402 is HTTP-native and stablecoin-settled today. MPP is Stripe + Tempo's card-rail counterpart aimed at machine-to-machine card payments. They are complementary rails, not substitutes.

Full comparison →MPP deep dive →
x402 vs ACP

x402 settles per-call API payments. ACP settles consumer checkout in conversational surfaces (ChatGPT). x402 is API-side, ACP is checkout-side.

Full comparison →ACP deep dive →
x402 vs AP2

AP2 is the governance spec for agent payments. x402 is a settlement rail. AP2 implementations frequently use x402 as the stablecoin rail.

Full comparison →AP2 deep dive →
Adjacent protocols

Other protocols in the same neighbourhood.

MPP
Machine Payments Protocol
MPP

A card-rail protocol for machine-to-machine payments.

Build with xpay

We are the policy engine on top of x402.

Smart ProxyAll protocols
Primary sources
x402 — Coinbase Developer Platform ↗Cloudflare blog: HTTP 402 awakens ↗
x402 Logo

We're building essential tools that sit between AI agents and autonomous payments, ensuring agents never overspend while enabling instant API monetization.

or ask your AI app
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