> ## Documentation Index
> Fetch the complete documentation index at: https://docs.primev.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# What is Fastx402?

> An x402 payment facilitator for AI agents — sub-second USDC settlement on Ethereum mainnet.

Fastx402 is an [x402](https://www.x402.org/) payment facilitator that lets AI agents and applications pay for resources on Ethereum mainnet using USDC. It achieves sub-second settlement through [FAST RPC](/v1.2.x/knowledge-base/what-is-fast-rpc) preconfirmations.

## The Problem

Ethereum's 12+ second finality makes it unsuitable for real-time agent payments. An AI agent that needs to pay for an API call can't wait 12 seconds for confirmation — it needs a response in milliseconds. Existing x402 facilitators solve this by operating on Base or Solana, but that means agents can't access Ethereum's deep USDC liquidity.

## How It Works

Fastx402 uses USDC's native EIP-3009 `transferWithAuthorization` function for gasless, signature-based payments:

1. An agent encounters a `402 Payment Required` response from a resource server.
2. The agent signs an EIP-712 authorization message — no on-chain transaction needed.
3. The resource server forwards the signed payment to Fastx402's `/settle` endpoint.
4. Fastx402 verifies the signature and submits the transaction via FAST RPC.
5. FAST RPC preconfirms the transaction in \~100-200ms.
6. The resource server receives confirmation and grants access.

## Key Features

* **Sub-second settlement** — \~1.2 seconds end-to-end via FAST RPC preconfirmations (vs 12+ seconds on standard Ethereum).
* **Zero gas for agents** — Agents only need USDC. A relay wallet submits the on-chain transaction and covers gas.
* **Zero fees** — No facilitator fee during the promotional period.
* **Mainnet liquidity** — Access Ethereum's largest stablecoin issuance and DeFi ecosystem directly.
* **x402 compatible** — Drop-in replacement for any x402 facilitator. Works with the standard x402 flow.

***

## Learn More

<CardGroup cols={2}>
  <Card title="Fastx402 Developer Docs" icon="code" href="/v1.2.x/developers/fastx402">
    Full API reference, EIP-3009 signing guide, and error codes.
  </Card>

  <Card title="What is FAST RPC?" icon="circle-question" href="/v1.2.x/knowledge-base/what-is-fast-rpc">
    The preconfirmation RPC that powers Fastx402 settlement.
  </Card>
</CardGroup>