A-Identity Docs : Passport & Wallet for the Agentic Economy

Arc is an EVM chain from Circle where gas is paid in USDC, not a volatile native token, with sub-second deterministic finality. For an agent that just wants to pay for a thing, that removes a whole class of failure. A-Identity uses Arc as its primary settlement rail.

A USDC coin pays gas as Arc produces blocks — Gas is paid in USDC, and blocks finalize in well under a second.

Why Arc

USDC is the gas

No second token to hold, price, or refill. The agent pays fees in the same dollar it is already moving.

Sub-second finality

Deterministic finality in well under a second. The payment either happened or it did not, and the agent knows at once.

EVM compatible

Standard Ethereum bytecode and RPC. ERC-8004 identity and x402 payments port over with no rewrite.

Arc Mainnet opened on 2026-09-16 and A-Identity went live on it that day (see Arc Mainnet below). Escrow, KYA anchoring and the account-abstraction path still run on Arc Testnet, and the rest of this page targets it unless a section says Mainnet. Get testnet USDC from the Circle faucet. What we did here is on the record: agent #849980, the KYA attestation and the first reputation anchor our oracle ever wrote are each listed with their transaction at /proof/arc, and the index over every chain is at /proof.

Network Config

Field	Value
Chain ID	`5042002`
Native currency	USDC (18 decimals)
RPC (HTTP)	`https://rpc.testnet.arc.io`
RPC (WebSocket)	`wss://rpc.testnet.arc.io`
Block explorer	explorer.testnet.arc.io
Faucet	faucet.circle.com

Arc has a dual USDC interface: the native balance uses 18 decimals while the ERC-20 interface uses 6. Both point at the same underlying balance. Set display decimals correctly or amounts will look off by a factor of a trillion.

Arc Mainnet

Arc Mainnet is in the registry as arc-mainnet with status live since 2026-09-16, the day it opened: agent #0 on the canonical registry is ours, an AgentSpendPolicy vault (0xe07819e6d28a5dfd5a9f4cd94dc6dc9aeeda4146) holds real USDC under dust caps, and paid calls settled through both our EIP-3009 facilitator and Circle Gateway nanopayments. Every payment so far is self-funded and labeled internal; each transaction is listed at /proof/arc. It is a separate descriptor from the testnet on purpose, with its own signer variable (ARC_MAINNET_SIGNER_KEY), so a testnet key can never become a mainnet key by a rename.

Field	Value
Chain ID	`5042`
RPC (HTTP)	`https://rpc.mainnet.arc.io` (plus Blockdaemon, dRPC and QuickNode hosts under `mainnet.arc.io`)
Block explorer	explorer.arc.io, pages open in a browser; its JSON API challenges non-browser clients
USDC (ERC-20 interface)	`0x3600000000000000000000000000000000000000`, the same predeploy address as testnet
ERC-8004 identity	`0x8004a169fb4a3325136eb29fa0ceb6d2e539a432`
ERC-8004 reputation	`0x8004BAa17C55a88189AE136b182e5fdA19dE9b63`
CCTP V2	domain `26`, TokenMessengerV2 `0x28b5a0e9C621a5BadaA536219b3a228C8168cf5d`
Circle Gateway	GatewayWallet `0x77777777Dcc4d5A8B6E418Fd04D8997ef11000eE`

The ERC-8004 registries on Arc Mainnet are not the testnet addresses. The testnet set (0x8004A818...) has no code on mainnet; mainnet carries the canonical family that Base, Arbitrum One, X Layer and Celo share. A 130-byte proxy at an address proves nothing by itself, so the pair was checked by reading each proxy’s EIP-1967 implementation slot and matching the implementation code against Base. There is no ValidationRegistry on mainnet, and Arc’s reference ERC-8183 contract is documented for testnet only.

What stays on testnet until it has its own evidence: Circle developer-controlled wallets (Circle’s Wallets table lists the ARC mainnet chain code, but our wallet path has not created or used one there yet), Paymaster (Circle’s Paymaster addresses page lists no Arc network, and its v0.7 and v0.8 addresses have no code on Arc mainnet), the account-abstraction path, the treasury and airdrop demos, and ERC-8183 escrow (Arc’s reference contract has code on testnet and none on mainnet). docs.arc.io describes the mainnet RPC endpoints as permissioned during a private-mainnet phase; they answered without credentials on launch day, and ARC_MAINNET_RPC_URL takes a credentialed endpoint if that changes. The explorer’s pages open in a browser without signing in; only its JSON API answers non-browser clients with a bot challenge.

Connect With viem

import { defineChain } from 'viem'

export const arcTestnet = defineChain({
  id: 5042002,
  name: 'Arc Testnet',
  nativeCurrency: { name: 'USD Coin', symbol: 'USDC', decimals: 18 },
  rpcUrls: {
    default: {
      http: ['https://rpc.testnet.arc.io'],
      webSocket: ['wss://rpc.testnet.arc.io'],
    },
  },
  blockExplorers: {
    default: { name: 'Arc Testnet Explorer', url: 'https://explorer.testnet.arc.io' },
  },
  testnet: true,
})

import { createPublicClient, http } from 'viem'
import { arcTestnet } from './chain'

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

// Read-only, no keys needed.
const chainId = await client.getChainId()      // 5042002
const block = await client.getBlockNumber()    // latest block

A-Identity already does this read for you. Hit the live backend (or a local server at http://localhost:3399):

# live deployment
curl https://a-identity-backend.onrender.com/api/arc
# { "online": true, "chainId": 5042002, "blockNumber": "...", "gasToken": "USDC", ... }

# or read the deployed ERC-8004 + ERC-8183 + USDC contracts, live and unmocked
curl https://a-identity-backend.onrender.com/api/arc/contracts

Unified Balance With App Kit

Circle App Kit pools USDC from several chains into one spendable balance (Circle Gateway), so an agent is never stuck with funds on the wrong chain.

Install

npm install @circle-fin/app-kit @circle-fin/adapter-viem-v2 viem

Deposit from any chain

await kit.unifiedBalance.deposit({
  from: { adapter: viemAdapter, chain: 'Base_Sepolia' },
  amount: '1.00',
  token: 'USDC',
})

Spend on Arc

await kit.unifiedBalance.spend({
  amount: '1.50',
  from: { adapter: viemAdapter },
  to: { adapter: viemAdapter, chain: 'Arc_Testnet', recipientAddress: '0x...' },
})

In A-Identity, the Wallet screen shows this unified balance, and deposit or spend above your limit pauses for human approval.

Deploy A Contract

Arc deploys with the standard EVM toolchain. Gas is paid in USDC, so fund the deployer wallet from the faucet first.

Install Foundry

curl -L https://foundry.paradigm.xyz | bash
foundryup

Create and fund a wallet

cast wallet new
# then request testnet USDC at https://faucet.circle.com

Deploy

forge create src/Counter.sol:Counter \
  --rpc-url https://rpc.testnet.arc.io \
  --private-key $PRIVATE_KEY \
  --broadcast

A-Identity never deploys a contract or moves real value on its own. Deployment holds a key, so it is human-on-the-loop: a person runs it and approves it.

Where Arc Fits

Arc is the primary rail: gas in USDC, a unified balance via Circle Gateway, native-USDC bridging via CCTP, and sub-cent x402 settlement, either on-chain or gasless via Nanopayments. Base and the other chains are fallbacks. Identity stays on ERC-8004, which Arc speaks natively because it is EVM compatible.

Get Started

About

Live on OKX.AI

Concepts

Protocols

Chains

The App

Build on Arc

Why Arc

USDC is the gas

Sub-second finality

EVM compatible

Network Config

Arc Mainnet

Connect With viem

Unified Balance With App Kit

Deploy A Contract

Where Arc Fits

​Why Arc

USDC is the gas

Sub-second finality

EVM compatible

​Network Config

​Arc Mainnet

​Connect With viem

​Unified Balance With App Kit

​Deploy A Contract

​Where Arc Fits

Why Arc

Network Config

Arc Mainnet

Connect With viem

Unified Balance With App Kit

Deploy A Contract

Where Arc Fits