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Arc

Arc is Circle's own chain. USDC is its gas coin, so a player who holds USDC on Arc needs nothing else to pay: no ETH, no second token. Arc is built in and on by default next to the other EVM chains, for the same wallet= address. Blocks are final as soon as they're made, so a payment counts within about a second.

init python:
    scfg.configure(wallet="0xYourWallet", testnet=True)    # offers Arc Testnet too

    # Or leave Arc out:
    scfg.configure(wallet="0xYourWallet", chains=["arbitrum", "base", "polygon", "ethereum"])
  • Your wallet must be usable on Arc. A normal wallet address (MetaMask, Rabby, a hardware wallet…) is the same on every EVM chain, Arc included. A smart-contract wallet (a Safe or another multisig, or a smart account) exists only on the chains it was deployed to. If yours isn't deployed on Arc, payments there land at an address you can't control. Leave Arc out with chains= until it is.
  • USDC only. USDT isn't on Arc, so items priced in USDT simply don't offer it. tokens=["USDT"] leaves Arc out entirely.
  • Every way of paying is found. A wallet's "Send" button moves USDC as Arc's native coin. A browser checkout or phone QR calls USDC's ERC-20 interface (0x3600000000000000000000000000000000000000). An exchange withdrawal does either. The game reads every one from the same place (Arc's USDC event log), so each payment counts exactly once.
  • Only six decimals count. A native send can carry up to 18 decimals; the game reads the first 6, as for every USDC (4.9937421… counts as 4.993742). A move of less than a millionth of a USDC is never a payment.
  • Wallets. MetaMask, Rabby, Coinbase Wallet and Rainbow can add Arc (chain id 5042; testnet 5042002). The browser checkout adds it for the player when the wallet asks. Some wallets show the native balance labelled "ETH": on Arc it is USDC. The checkout page warns the player when paying would leave less than 0.01 USDC for the fee.
  • Fee floor. Arc drops transactions priced under 20 gwei without an error, so the browser checkout always sets at least that. A fee costs about 0.001 USDC.
  • If the wallet won't quote a fee, the browser checkout can't build the transaction: it reads the network's gas price from the wallet before it sends. The player sees the wallet's error and can pay by QR or manual transfer instead.
  • Testing. testnet=True uses Arc Testnet. Get testnet USDC from faucet.circle.com (choose Arc Testnet). It pays the fee too. Before release, pay once with your wallet's own Send button (a native send) and once through the browser checkout (an ERC-20 transfer): the two arrive in different ways.

Upgrading to the version with Arc built in​

  • Arc appears on its own. If you don't pass chains=, the update adds Arc to your payment screen. Check that your wallet works on Arc (see above), or list your chains with chains= to keep the old set.
  • Did your game add Arc itself? Delete that add_chain() call. With the key "arc", the game otherwise stops at startup with chain 'arc' is built in. Purchases it recorded stay valid and are still re-checked at each launch.
  • Under another key (say "arc_mainnet"), the game stops with chain 'arc_mainnet' has the same chain_id (5042) as 'arc'. Delete that call too. Purchases stored under the old key stay owned, but the game no longer re-checks them on-chain (it keeps receipts of chains it doesn't know). New purchases are stored under "arc".