x402

live

x402 Payment Protocol

by Coinbase· launched 2025-05verified 2026-09-03

At a glance

Layer
execution
Category
onchain
Rails
USDC, Base, Solana, stablecoins
Settlement
On-chain stablecoin (USDC) settled via facilitators.
Reversible
No
Human in loop
none
D2C fit
moderate
B2B fit
strong
Spec
https://www.x402.org/

Revives the dormant HTTP 402 status code: a server answers a request with 402 and machine-readable payment requirements, the agent signs and pays in stablecoin, a facilitator verifies and settles on-chain, and the request is retried with a payment header. Governance transferred to the vendor-neutral x402 Foundation under the Linux Foundation in 2026, with 40 founding members including Visa, Mastercard, Stripe, Adyen, and AWS.

How it works

x402 turns the long-unused HTTP 402 "Payment Required" status into a working payment handshake between clients and servers, with no accounts or API keys.

  1. Challenge. A client requests a protected resource. Instead of 200, the server returns 402 with a machine-readable body describing what is owed — amount, asset (typically USDC), destination, network, and an expiry.
  2. Pay. The client (an agent's wallet) constructs and signs a payment payload authorizing the transfer, and retries the request with the signed payload attached in an X-PAYMENT header.
  3. Verify & settle. The server hands the payload to a facilitator — a pluggable service that verifies the signature and settles the transfer on-chain. Merchants can use a hosted facilitator or self-host their own.
  4. Fulfil. Once settlement is confirmed, the server returns the resource (200) along with a settlement receipt.

Because settlement rides on stablecoin rails, payments are push-based and final. The design contemplates deferred/batched settlement so that many sub-cent calls can be aggregated rather than settled individually, mitigating per-transaction gas overhead.

Protocol V2 (mid-2026) introduced CAIP-2 network identifiers, scoped @x402/* npm packages, new header names (PAYMENT-REQUIRED, PAYMENT-SIGNATURE, PAYMENT-RESPONSE), a Bazaar discovery extension, and support for exact, upto, and batch-settlement payment schemes. Coinbase contributed the protocol to the Linux Foundation in April 2026; the x402 Foundation became operationally active in July 2026 with 40 members spanning payments incumbents (Visa, Mastercard, Amex, Adyen, Fiserv, Stripe), cloud providers (AWS, Google, Cloudflare), and blockchain ecosystems.

Tradeoffs

  • Payments are non-reversible: there is no built-in chargeback, dispute, or refund mechanism, so error handling and trust must be solved out-of-band.
  • Latency is bounded by on-chain confirmation, which is slower than an authorize-now/capture-later card flow.
  • Sub-cent, per-call pricing runs into gas economics unless calls are batched or deferred.
  • Custody shifts to the agent: the paying party must hold and manage keys (MPC wallets or scoped session keys), expanding the attack surface.

Security & limitations

  • Documented attack classes include unpaid-service and paid-but-denied failures, where either side of the exchange defaults after the other performs.
  • Payment metadata (resource URL, description, reason) can travel in plaintext, creating PII-leakage and transaction-linkability risk.
  • Prompt-injection against the paying agent can induce fraudulent or over-value payments, since the agent both decides and authorizes.
  • Replay and overpayment drain are concerns without strict nonce/expiry handling and per-request payment caps.

See sources below. Documented for commentary and identification only.

Fits together with

  • MPP — Machine Payments Protocol (MPP)
  • ERC-4337 — ERC-4337 Account Abstraction

Deployments using x402

  • CoinGecko x402 Endpoints

    CoinGecko

    bothlive

    Market-data endpoints (token prices, on-chain data) exposed as pay-per-request: a flat $0.01 USDC per call, no account or API key required.

    Chains
    Base, Solana
    Launched
    2026-03
    verified 2026-09-02source

  • Coinbase Agent.market

    Coinbase

    bothlive

    An x402-native marketplace / app-store for agent services: an operator publishes an endpoint and sets a price, and any x402-aware agent can discover and pay for it with no contract or onboarding.

    Chains
    Base
    verified 2026-09-02source

  • Cloudflare Agents SDK + Monetization Gateway

    Cloudflare

    bothlive

    x402 integrated into Cloudflare Workers: an Agents SDK example gates routes behind a price, and an x402-proxy Worker template sits in front of any origin to charge agents (and crawlers) per request.

    Chains
    Base, Base Sepolia
    verified 2026-09-02source

  • Circle Wallets + x402 Reference Workflow

    Circle

    bothlive

    A reference workflow for autonomous agents: provision a Circle MPC developer wallet, fund it with USDC, and clear x402 paywalls via the Circle Signing API (EIP-3009 transferWithAuthorization).

    Chains
    Base
    verified 2026-09-02source

  • ZeroClick

    ZeroClick

    bothlive

    A storefront and paid-proxy layer that turns any API into an agent-purchasable service: agents discover a seller's machine-readable pay URL, pay per request or by plan over x402 (Stripe's MPP is also supported), and ZeroClick verifies payment, signs the call, and forwards it to the origin — settling revenue to the seller's Stripe account in USDC or fiat.

    Chains
    Base, Tempo
    verified 2026-09-02source

  • Polygon x402 Facilitators

    Polygon

    bothlive

    x402 v2 facilitators on Polygon mainnet and Amoy testnet: sellers accept USDC micropayments for APIs and agent services with sub-2-second settlement, low fees, and gas sponsorship via the Coinbase CDP facilitator.

    Chains
    Polygon
    Launched
    2026-03
    verified 2026-09-07source

  • X Pay x402 Gateway

    X-Pay Technologies

    bothlive

    An x402 payment gateway on Base mainnet: any HTTP endpoint can name a price, take payment in USDC, and serve its response in a single request — with no account, API key, or subscription. Includes session keys with spending limits, merchant dashboards, and 1% of settled volume pricing.

    Chains
    Base
    Launched
    2026-09
    verified 2026-09-14

  • Circle x402 Facilitator Service on Arc

    Circle

    bothlive

    A hosted x402 facilitator that lets sellers accept USDC payments from AI agents across Arc, Base, and Polygon through a single integration — no relayer keys, gas wallets, or per-chain settlement infrastructure required. Circle verifies buyer-signed EIP-3009 authorizations, screens both parties, and settles on-chain. Launched with Arc mainnet (September 16, 2026); agentic payments announced live September 19.

    Chains
    Arc, Base, Polygon
    Launched
    2026-09
    verified 2026-09-23source

Sources

  1. [1]x402 — official protocol site— x402 Foundation
  2. [2]x402 documentation (Welcome)— Coinbase Developer Platform
  3. [3]x402 Foundation — reference implementation (post-contribution)— x402 Foundation (GitHub)
  4. [4]Linux Foundation Announces Operational Launch of x402 Foundation— Linux Foundation, 2026-07-14
  5. [5]Linux Foundation is Launching the x402 Foundation (initial announcement)— Linux Foundation, 2026-04-02
  6. [6]Migration Guide: V1 to V2— x402 Foundation