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The EIP-2612 gas sponsoring extension enables gasless Permit2 approval for tokens that implement the EIP-2612 permit() function (e.g., USDC). The client signs an off-chain permit authorizing the Permit2 contract, and the facilitator submits it atomically during settlement via x402ExactPermit2Proxy.settleWithPermit.

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Overview

When using the Permit2 asset transfer method, the user must first approve the Permit2 contract to spend their tokens. For tokens that support EIP-2612, this approval can be done entirely off-chain:
  • For Buyers: No gas needed — sign a permit off-chain and the facilitator handles the rest
  • For Sellers: Advertise this extension so clients using EIP-2612 tokens get a seamless experience
  • For Facilitators: Accept the permit signature and call settleWithPermit to atomically approve + settle in one transaction

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How It Works

  1. Server advertises eip2612GasSponsoring in the PaymentRequired response extensions
  2. Client checks if Permit2 allowance is insufficient; if so, signs an EIP-2612 permit off-chain
  3. Client includes the permit data in the extensions.eip2612GasSponsoring.info field of the payment payload
  4. Facilitator calls x402ExactPermit2Proxy.settleWithPermit(), which atomically submits the EIP-2612 permit and executes the Permit2 transfer in a single transaction

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Server Usage

Advertise support for this extension in your route configuration: 
import { declareEip2612GasSponsoringExtension } from "@x402/extensions/eip2612-gas-sponsoring";

const routes = {
  "GET /api/data": {
    accepts: [{
      scheme: "exact",
      network: "eip155:84532",
      price: "$0.01",
      payTo: "0xYourAddress",
    }],
    extensions: {
      ...declareEip2612GasSponsoringExtension(),
    },
  },
};

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Client Usage

The ExactEvmScheme handles EIP-2612 gas sponsoring automatically. When the server advertises this extension and the client’s Permit2 allowance is insufficient, the scheme signs the EIP-2612 permit and includes it in the payment payload. 
import { ExactEvmScheme } from "@x402/evm/exact/client";

// readContract capability is required for EIP-2612 (to check allowance and nonce)
const scheme = new ExactEvmScheme(signer);
client.register("eip155:*", scheme);

// The scheme automatically signs an EIP-2612 permit when:
// 1. The server advertises eip2612GasSponsoring
// 2. The asset transfer method is "permit2"
// 3. The client's Permit2 allowance is insufficient

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When to Use

Use this extension when:
  • Your payment token implements EIP-2612 (has a permit() function)
  • You want fully gasless Permit2 onboarding for your users
  • You’re using the permit2 asset transfer method
Common EIP-2612 tokens include USDC, DAI, and many modern ERC-20 tokens.

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SDK Support

SDKSupported
TypeScript✅
Go✅
Python✅