> ## Documentation Index
> Fetch the complete documentation index at: https://a-identity.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Build on Robinhood Chain

> Robinhood Chain network config for both networks, the canonical ERC-8004 registries already deployed there, and the x402 facilitator we run for it.

Robinhood Chain is Robinhood's own Arbitrum Orbit L2, built for tokenized real-world
assets, with ETH as the gas token and Ethereum for data availability. A-Identity runs
agent identity there, and settles paid trust calls there in USDG.

## Why this chain

<CardGroup cols={3}>
  <Card title="Agents will trade here" icon="chart-line">
    It is the chain built around tokenized stocks and ETFs, and Robinhood has opened its surfaces to AI agents while stating plainly that it does not supervise them. That gap is the product.
  </Card>

  <Card title="ERC-8004 is already live" icon="fingerprint">
    The canonical identity and reputation registries were deployed here by their authors, at the same addresses they carry on X Layer and Celo. Nothing had to be forked.
  </Card>

  <Card title="Gasless payments work" icon="bolt">
    USDG implements EIP-3009, so a buyer can sign a transfer and never touch gas. Our facilitator broadcasts it.
  </Card>
</CardGroup>

<Note>
  Mainnet (`4663`) is **live** for us: agent #0 on the canonical registry is ours, and
  paid trust calls settle here in USDG. Testnet (`46630`) is **beta**, and carries the
  full canonical ERC-8004 trio plus a deployed AgentSpendPolicy vault. Every claim on
  this page is checkable at [/proof/robinhood](https://a-identity.xyz/proof/robinhood).
</Note>

## Network config

| Field           | Mainnet                                                                | Testnet                                                                              |
| --------------- | ---------------------------------------------------------------------- | ------------------------------------------------------------------------------------ |
| Chain ID        | `4663`                                                                 | `46630`                                                                              |
| CAIP-2          | `eip155:4663`                                                          | `eip155:46630`                                                                       |
| Native currency | ETH (18 decimals)                                                      | ETH (18 decimals)                                                                    |
| RPC (HTTP)      | `https://rpc.mainnet.chain.robinhood.com`                              | `https://rpc.testnet.chain.robinhood.com`                                            |
| Block explorer  | [robinhoodchain.blockscout.com](https://robinhoodchain.blockscout.com) | [explorer.testnet.chain.robinhood.com](https://explorer.testnet.chain.robinhood.com) |
| Faucet          | n/a (bridge real ETH)                                                  | [faucets.chain.link/robinhood-testnet](https://faucets.chain.link/robinhood-testnet) |

<Warning>
  Two things will bite you here.

  **There is no canonical Circle USDC on either network.** Do not copy a USDC address
  from another chain: it will not be the same token. The settlement token we use on
  mainnet is Paxos USDG at `0x5fc5360D0400a0Fd4f2af552ADD042D716F1d168`, which is the
  address Paxos documents for this chain. Our registry deliberately leaves the USDC slot
  empty and names USDG as its own thing.

  **CreateX is not deployed here**, on either network, so CREATE3 is unavailable. The
  deterministic deployer that IS present is the Safe Singleton Factory
  (`0x914d7Fec6aaC8cd542e72Bca78B30650d45643d7`), alongside the Arachnid CREATE2 factory.
  That is what makes the canonical ERC-8004 addresses reproducible here.
</Warning>

## Connect with viem

<CodeGroup>
  ```ts chain.ts theme={null}
  import { defineChain } from 'viem'

  export const robinhoodChain = defineChain({
    id: 4663,
    name: 'Robinhood Chain',
    nativeCurrency: { name: 'Ether', symbol: 'ETH', decimals: 18 },
    rpcUrls: { default: { http: ['https://rpc.mainnet.chain.robinhood.com'] } },
    blockExplorers: { default: { name: 'Blockscout', url: 'https://robinhoodchain.blockscout.com' } },
  })

  export const robinhoodTestnet = defineChain({
    id: 46630,
    name: 'Robinhood Chain Testnet',
    nativeCurrency: { name: 'Ether', symbol: 'ETH', decimals: 18 },
    rpcUrls: { default: { http: ['https://rpc.testnet.chain.robinhood.com'] } },
    blockExplorers: { default: { name: 'Blockscout', url: 'https://explorer.testnet.chain.robinhood.com' } },
  })
  ```

  ```ts read.ts theme={null}
  import { createPublicClient, http } from 'viem'
  import { robinhoodChain } from './chain'

  const client = createPublicClient({ chain: robinhoodChain, transport: http() })

  // Agent #0 is the first agent ever registered on this chain.
  const owner = await client.readContract({
    address: '0x8004a169fb4a3325136eb29fa0ceb6d2e539a432',
    abi: [{ type: 'function', name: 'ownerOf', stateMutability: 'view', inputs: [{ type: 'uint256' }], outputs: [{ type: 'address' }] }],
    functionName: 'ownerOf',
    args: [0n],
  })
  ```
</CodeGroup>

## What is deployed

| Contract           | Network | Address                                                                                                                                         |
| ------------------ | ------- | ----------------------------------------------------------------------------------------------------------------------------------------------- |
| IdentityRegistry   | mainnet | [`0x8004a169fb4a3325136eb29fa0ceb6d2e539a432`](https://robinhoodchain.blockscout.com/address/0x8004a169fb4a3325136eb29fa0ceb6d2e539a432)        |
| ReputationRegistry | mainnet | [`0x8004BAa17C55a88189AE136b182e5fdA19dE9b63`](https://robinhoodchain.blockscout.com/address/0x8004BAa17C55a88189AE136b182e5fdA19dE9b63)        |
| USDG (settlement)  | mainnet | [`0x5fc5360D0400a0Fd4f2af552ADD042D716F1d168`](https://robinhoodchain.blockscout.com/address/0x5fc5360D0400a0Fd4f2af552ADD042D716F1d168)        |
| IdentityRegistry   | testnet | [`0x8004A818BFB912233c491871b3d84c89A494BD9e`](https://explorer.testnet.chain.robinhood.com/address/0x8004A818BFB912233c491871b3d84c89A494BD9e) |
| ReputationRegistry | testnet | [`0x8004B663056A597Dffe9eCcC1965A193B7388713`](https://explorer.testnet.chain.robinhood.com/address/0x8004B663056A597Dffe9eCcC1965A193B7388713) |
| ValidationRegistry | testnet | [`0x8004Cb1BF31DAf7788923b405b754f57acEB4272`](https://explorer.testnet.chain.robinhood.com/address/0x8004Cb1BF31DAf7788923b405b754f57acEB4272) |

We did not deploy the mainnet registries. They were already live at their canonical
cross-chain addresses when we arrived; what is ours is **agent #0**, the first token that
registry ever minted. On testnet the ValidationRegistry implementation was the one piece
missing, and we deployed it by replaying the canonical Safe-Singleton-Factory calldata,
which reproduces the same address rather than forking a new one.

There is **no ValidationRegistry in the mainnet family**, mirroring Celo and X Layer, so
a KYA result cannot be anchored on-chain there. It is still verified off-chain and
recorded; we simply do not claim an anchor that does not exist.

## The x402 facilitator

An x402 facilitator is the service a seller calls to verify a payment and settle it. No
published facilitator serves this chain, so a seller here has nothing to point an x402
client at. We run one, and it is open:

To be precise about what that does and does not claim: gasless EIP-3009 relaying on USDG
predates us on this chain by weeks, and an x402 settlement is indistinguishable on-chain
from any other relayed authorization. What we could not find, and therefore built, is a
facilitator serving the x402 HTTP protocol here.

| Endpoint                         | Access                                       |
| -------------------------------- | -------------------------------------------- |
| `GET /api/facilitator/supported` | open                                         |
| `POST /api/facilitator/verify`   | open, read-only                              |
| `POST /api/facilitator/settle`   | allowlisted by payTo, because we pay the gas |
| `GET /api/facilitator/proof`     | open                                         |

Base URL: `https://a-identity-backend.onrender.com/api/facilitator`. Both x402 wire
spellings are accepted for `network`: the v1 slug (`rhchain`) and the v2 CAIP-2 id
(`eip155:4663`).

The signing domain is **proven, not pasted**. USDG exposes neither `version()` nor
`eip712Domain()`, so the EIP-712 domain cannot be read from the contract. We rebuild each
candidate domain and accept only the one that reproduces the live `DOMAIN_SEPARATOR`. If
none matches, no payment challenge is served at all, because inviting a buyer to sign
against a guessed domain produces an authorization nobody can settle.

## Verify it yourself

```bash theme={null}
# The signing domain, straight from the token. Compare it to what /supported publishes.
curl -sX POST https://rpc.mainnet.chain.robinhood.com -H 'content-type: application/json' \
  -d '{"jsonrpc":"2.0","id":1,"method":"eth_call","params":[{"to":"0x5fc5360D0400a0Fd4f2af552ADD042D716F1d168","data":"0x3644e515"},"latest"]}'
# -> 0x7a3d7400b27830f4f91c2c16a082486d67c1befecaec2f53b33f1f35d5b62036

# Our provenance ledger, with a live re-read of ownerOf(0) on every request.
curl -s https://a-identity-backend.onrender.com/api/proof/robinhood

# Every settlement, with the transaction that proves it.
curl -s https://a-identity-backend.onrender.com/api/facilitator/proof
```

## Where this chain fits

Arc is where escrow and the spend vault live. X Layer is where the trust oracle is
listed. Celo is where x402 settles through a first-party facilitator someone else runs.
Robinhood Chain is the one where we had to build the rail ourselves, and it is the chain
whose users are agents trading real-world assets, which is exactly the population that
needs a policy layer in front of it.