Arc Mainnet vs Testnet: What Changed on September 16

Arc ran in public rehearsal for nearly eleven months — testnet live since October 28, 2025, processing around 13.5 million transactions a week by late summer. On September 16, 2026, the real network opened. This page sorts exactly what changed at the flip, what deliberately stayed identical, and the questions the transition actually raises: do balances carry over (no), is testnet dead (no), and which network should you be using for what.

What are the two networks, side by side?

Mainnet parameters live on the mainnet-live page, which updates against Circle's official publications. Everything else about the two networks — the EVM, Malachite consensus, ~780ms deterministic finality, USDC-as-gas at 18 protocol decimals — is the same by design: testnet's job was to be a faithful rehearsal.

Do testnet balances or deployments carry over?

No, and this is the question that catches newcomers. Testnet and mainnet are separate ledgers with separate state. Test USDC was always valueless faucet money; tokens you minted, pools you created, and locks you set on testnet exist only on testnet. Anything you want on mainnet gets deployed again, for real, on mainnet — which is why the launch checklist treats the testnet run-through as a dress rehearsal whose script you then execute on the real stage.

The corollary scam warning: nobody legitimate will ever offer to "migrate" or "convert" your testnet balances to mainnet. Testnet activity has no announced reward attached to it — no airdrop exists (ARC token status) — and any site claiming to convert test balances is phishing.

Is testnet still useful now that mainnet is live?

More than ever, and it remains live and maintained. Testnet is where you rehearse anything before doing it with real money: developers test contract deployments against a faithful copy of mainnet's environment; founders run the full mint-pool-lock-vest sequence with faucet USDC before spending real USDC; and newcomers learn wallet mechanics with zero downside. The testnet guide covers faucet access and first transactions. The mental model: mainnet is production, testnet is staging, and the discipline of staging-first survives the launch.

What actually changed in practice?

Three things with teeth. Value: fees are now real dollars (still cents — testnet averaged ~$0.004 and mainnet fees remain dollar-denominated in USDC), and mistakes are now real mistakes with no faucet to refill you. Finality's meaning: sub-second deterministic settlement was a benchmark on testnet; on mainnet it's irreversibility of real money — the same ~780ms now means "gone means gone," which is why address-checking habits matter (sending USDC safely). And the audience: testnet's population was builders and farmers; mainnet brings real buyers, real liquidity, and — immediately — real scammers, which changes how much the trust infrastructure (locks, vesting, verified contracts) matters from day one.

Which network should you be on right now?

If you're moving real value or trading: mainnet, with the parameters from the official sources only. If you're testing, learning, or rehearsing a launch: testnet, deliberately, until the flow is boring — then mainnet. If you're a project founder, the strongest pattern is both in sequence: full rehearsal on testnet, immediate real deployment on mainnet with the same script, locks and vesting included (why that order). The one thing not to do is treat testnet as a lesser mainnet — it's a different tool, and using each for its job is the whole point of Circle running both.

FAQ

Did my testnet USDC become real USDC at mainnet launch? No. Test USDC is faucet money on a separate ledger and has no value. Nothing carries over, and no conversion mechanism exists — offers to convert are scams.

Is Arc testnet shutting down? No — testnet remains live alongside mainnet, as staging environments do. Chain ID 5042002, faucet at faucet.circle.com.

Are testnet and mainnet technically identical? By design they share the EVM environment, consensus (Malachite, ~780ms deterministic finality), and USDC-as-gas model. They differ in chain ID, endpoints, state, and — decisively — whether the money is real.

Was there a reward for testnet participation? None has been announced. No ARC token exists and no airdrop has been announced; treat any "testnet reward claim" site as phishing.

Where do I find the real mainnet parameters? The mainnet-live page, arc.io, or circle.com — nowhere else. Fake RPC endpoints are a launch-week attack vector.