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Fastx402 is an x402 payment facilitator that enables AI agents and applications to pay for resources on Ethereum mainnet using USDC. It achieves sub-second settlement through FAST RPC preconfirmations, solving the slow finality problem that has left agents unable to access Ethereum’s stablecoin liquidity for real-time payments.
PropertyValue
Endpointhttps://facilitator.primev.xyz
NetworkEthereum Mainnet (Chain ID: 1)
AssetUSDC (0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48)
SettlementFAST RPC (~100-200ms preconfirmation)
Fees0%
SourceGitHub

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Why Fastx402

Traditional Ethereum payments require 12+ seconds for finality, making them unsuitable for real-time API access. Existing x402 facilitators only work on Base and Solana. Fastx402 changes this:
  • Sub-second settlement — ~1.2s end-to-end via FAST RPC preconfirmations (vs 12+ seconds)
  • Zero gas for agents — Agents only need USDC, no ETH required. Gas is fully sponsored via the relay wallet
  • Mainnet liquidity — Access Ethereum’s largest stablecoin issuance and DeFi ecosystem
  • x402 compatible — Drop-in replacement for any x402 facilitator
  • Gasless signatures — Uses EIP-3009 transferWithAuthorization so agents never submit transactions

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How It Works

Fastx402 uses USDC’s native EIP-3009 transferWithAuthorization function for gasless, signature-based payments. The flow:
  1. An agent encounters a 402 Payment Required response from a resource server
  2. The agent signs an EIP-712 TransferWithAuthorization message authorizing a USDC transfer
  3. The resource server forwards the signed payment to Fastx402’s /settle endpoint
  4. Fastx402 verifies the signature, checks balances and nonces, then submits the transaction via FAST RPC
  5. FAST RPC preconfirms the transaction in ~100-200ms
  6. The resource server receives confirmation and grants access
Agent                     Resource Server              Fastx402                  FAST RPC / L1
 │                              │                          │                          │
 │  GET /resource               │                          │                          │
 │ ──────────────────────────>  │                          │                          │
 │                              │                          │                          │
 │  <── 402 Payment Required    │                          │                          │
 │      (paymentRequirements)   │                          │                          │
 │                              │                          │                          │
 │  (sign EIP-3009 authorization locally)                  │                          │
 │                              │                          │                          │
 │  GET /resource + signature   │                          │                          │
 │ ──────────────────────────>  │                          │                          │
 │                              │  POST /settle            │                          │
 │                              │ ──────────────────────>  │                          │
 │                              │                          │  transferWithAuthorization│
 │                              │                          │ ──────────────────────>   │
 │                              │                          │  <── preconfirmed         │
 │                              │  <── { success: true }   │                          │
 │                              │                          │                          │
 │  <── 200 OK + resource       │                          │                          │

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API Reference

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POST /settle

Verify a payment signature and settle it on-chain via FAST RPC. Request body: 
{
  "paymentPayload": {
    "x402Version": 2,
    "scheme": "exact",
    "network": "eip155:1",
    "payload": {
      "signature": "0x...",
      "authorization": {
        "from": "0x...",
        "to": "0x...",
        "value": "1000000",
        "validAfter": "0",
        "validBefore": "1718000000",
        "nonce": "0x..."
      }
    }
  },
  "paymentRequirements": {
    "scheme": "exact",
    "network": "eip155:1",
    "amount": "1000000",
    "asset": "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48",
    "payTo": "0x...",
    "maxTimeoutSeconds": 60
  }
}
Response (success): 
{
  "success": true,
  "payer": "0x...",
  "transaction": "0x...",
  "network": "eip155:1"
}
Response (failure): 
{
  "success": false,
  "error": "insufficient_funds",
  "payer": "0x..."
}

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POST /verify

Validate a payment signature without settling (dry run). Same request body as /settle. 
{
  "isValid": true,
  "payer": "0x..."
}

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GET /supported

Discover facilitator capabilities. 
{
  "kinds": [
    {
      "x402Version": 2,
      "scheme": "exact",
      "network": "eip155:1"
    }
  ],
  "extensions": ["bazaar"],
  "signers": {
    "eip155:*": ["0x488d87a9A88a6A878B3E7cf0bEece8984af9518D"]
  }
}

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GET /health

Health check endpoint.

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EIP-3009 Signing

Agents sign a TransferWithAuthorization typed data message using USDC’s EIP-712 domain: 
const signature = await walletClient.signTypedData({
  domain: {
    name: 'USD Coin',
    version: '2',
    chainId: 1,
    verifyingContract: '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48',
  },
  types: {
    TransferWithAuthorization: [
      { name: 'from', type: 'address' },
      { name: 'to', type: 'address' },
      { name: 'value', type: 'uint256' },
      { name: 'validAfter', type: 'uint256' },
      { name: 'validBefore', type: 'uint256' },
      { name: 'nonce', type: 'bytes32' },
    ],
  },
  primaryType: 'TransferWithAuthorization',
  message: {
    from: agentAddress,
    to: merchantAddress,
    value: BigInt(1_000_000), // 1 USDC (6 decimals)
    validAfter: 0n,
    validBefore: BigInt(Math.floor(Date.now() / 1000) + 900),
    nonce: `0x${randomBytes(32).toString('hex')}`,
  },
});
The relay wallet (0x488d87a9A88a6A878B3E7cf0bEece8984af9518D) submits the transferWithAuthorization call on-chain. The agent never needs ETH — only USDC.

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Error Codes

CodeDescription
unsupported_schemeScheme is not “exact”
unsupported_networkNetwork is not “eip155:1”
unsupported_assetAsset is not USDC
invalid_from_addressInvalid sender address
recipient_mismatchauthorization.to does not match paymentRequirements.payTo
insufficient_paymentAuthorization value < required amount
authorization_expiredCurrent time + 60s >= validBefore
authorization_not_yet_validCurrent time < validAfter
invalid_signatureEIP-712 signature verification failed
insufficient_fundsPayer USDC balance < authorization value
nonce_already_usedNonce already consumed (replay protection)

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ERC-8004 Agent Identity

Fastx402 is registered as an on-chain agent via ERC-8004:
PropertyValue
Agent ID23175
Identity Registry0x8004A169FB4a3325136EB29fA0ceB6D2e539a432
Reputation Registry0x8004BAa17C55a88189AE136b182e5fdA19dE9b63
Metadata URI/agent.json