Build on Arc

Connect to Circle Arc, where agents pay gas in USDC. Network config, App Kit unified balance, and deploy steps.

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.

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.

Mainnet is not public yet. Everything here targets Arc Testnet. 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.network
RPC (WebSocket)	wss://rpc.testnet.arc.network
Block explorer	testnet.arcscan.app
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.

Connect With viem

chain.ts

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.network'],
      webSocket: ['wss://rpc.testnet.arc.network'],
    },
  },
  blockExplorers: {
    default: { name: 'Arcscan', url: 'https://testnet.arcscan.app' },
  },
  testnet: true,
})

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.

1. Install

   npm install @circle-fin/app-kit @circle-fin/adapter-viem-v2 viem
   
2. Deposit from any chain

   await kit.unifiedBalance.deposit({
     from: { adapter: viemAdapter, chain: 'Base_Sepolia' },
     amount: '1.00',
     token: 'USDC',
   })
   
3. 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.

1. Install Foundry

   curl -L https://foundry.paradigm.xyz | bash
   foundryup
   
2. Create and fund a wallet

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

   forge create src/Counter.sol:Counter \
     --rpc-url https://rpc.testnet.arc.network \
     --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.