Circle's open, EVM-compatible Layer 1 purpose-built for stablecoin finance, announced August 2025. Uses USDC as the native gas token, ships with a built-in onchain FX engine, and integrates CCTP V2 natively for cross-chain USDC. Targeted at banks, payment companies, and capital-markets infra rather than general-purpose DeFi. Currently in testnet (public testnet announced fall 2025) with mainnet expected late 2026.
- 01institutional stablecoin payments and settlement
- 02products that need USDC-denominated gas (no volatile fee token)
- 03onchain FX between USDC, EURC, and other Circle stablecoins
- 04capital-markets and tokenized money-market funds
- 05cross-chain USDC flows via native CCTP V2
- pnpm add viem wagmi
- # Arc is EVM-compatible — standard tooling works. Use Circle's Developer Console for testnet access.
| Variable | Scope | Description |
|---|---|---|
| NEXT_PUBLIC_ARC_RPC_URL | Client | Arc testnet RPC URL — obtain from Circle Developer Console (developers.circle.com). Mainnet not yet live as of mid-2026. |
| NEXT_PUBLIC_ARC_CHAIN_ID | Client | Arc chain ID — assigned per environment by Circle. Confirm in the Developer Console rather than hardcoding; the public testnet ID has shifted during preview phases. |
| CIRCLE_API_KEY | Server | Circle Developer API key for CCTP, Programmable Wallets, and Arc-specific endpoints (FX, KYC attestation). Server-only. |
Arc is EVM-compatible, so use viem with a custom chain definition: `defineChain({ id: ARC_CHAIN_ID, name: 'Arc', nativeCurrency: { name: 'USDC', symbol: 'USDC', decimals: 6 }, rpcUrls: { default: { http: [ARC_RPC_URL] } } })`. Two important departures from typical EVMs: (1) gas is paid in USDC (6-decimal native currency, not 18-decimal ETH) so all fee math must use 6 decimals; (2) CCTP V2 is built in — call the Arc CCTP contracts directly rather than wrapping USDC through a bridge. For onchain FX, use the Circle FX router (address published in Circle Developer Console). Until mainnet ships, treat all Arc work as testnet/preview; do not promise production timelines tied to Arc.
- ⚑Arc's native gas is USDC with 6 decimals — viem/wagmi default to 18-decimal nativeCurrency math; you must override or fee estimation will be off by 10^12.
- ⚑Arc is in testnet only as of mid-2026. Mainnet timing is publicly targeted for late 2026 but unconfirmed — never promise a customer-facing launch tied to Arc mainnet.
- ⚑Chain ID and contract addresses are subject to change during testnet phases; pull them from Circle Developer Console at runtime rather than hardcoding.
- ⚑Some standard EVM tooling (block explorers, indexers) may not yet support Arc — confirm Tenderly / Etherscan / Alchemy / Dune coverage before relying on it.
- ⚑Circle gates testnet access through their Developer Console — onboarding may require KYB for institutional flows, especially for FX and Issuance endpoints.
- ⚑CCTP V1 vs V2 differ materially: V2 supports hooks and fast finality. Always target V2 contracts on Arc; V1 may not be deployed there.