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Gasless swaps

With gasless mode on, you sign a swap instead of sending a transaction. An AchSwap relayer submits it on Arc Mainnet and pays the network gas. The tokens come from your wallet and the output goes back to it. The relayer cannot change the trade you signed.

What you can swap​

  • Pay with: USDC, EURC or cirBTC.
  • Receive: any token you can route to, including USDC.
  • Routes: KyberSwap, LI.FI and the AchSwap aggregator. If the best quote uses another route, gasless mode is not available for that swap.
  • Minimum size: each input token has a minimum USD value, set by AchSwap and applied on the swap screen. Smaller amounts, and exact-output quotes, go through a normal swap where you pay the gas.
  • Recipient: always your connected wallet. A custom recipient is not supported in gasless mode.

How a gasless swap works​

  1. One-time approval. The first time you use a token gaslessly, your wallet asks you to approve it for Permit2 (0x000000000022D473030F116dDEE9F6B43aC78BA3). You pay gas for this once per token. The swap continues automatically after it confirms.
  2. One signature. Your wallet shows a Permit2 message. It names the token and amount you pay and the AchSwap gasless executor as spender. It also contains the swap itself: the router, the token you receive, the minimum you accept, your address as recipient, and a hash of the exact route. Signing it does not cost gas.
  3. Relay. AchSwap's relayer checks the request and simulates it, then submits it. You see the transaction hash as soon as it is broadcast.
  4. Settlement. On chain, the executor pulls exactly the signed amount through Permit2 and runs the signed route. It then checks that your wallet received at least the minimum. If not, the whole transaction reverts and nothing leaves your wallet.

Earlier versions asked for two signatures per swap. The current executor needs one.

Fees​

Gasless mode adds no fee of its own. The route's normal fees still apply: the AchSwap aggregator fee, or the LI.FI and KyberSwap integrator fees, plus pool fees, as on a regular swap. See fees.

Cancelling and expiry​

A signed swap is valid only until the deadline in your swap settings. The relayer refuses deadlines more than three hours ahead. Each signature has a one-time Permit2 nonce, so it can execute at most once. To cancel a signature that has not executed yet, invalidate its nonce with Permit2's invalidateUnorderedNonces, or simply let it expire.

If a gasless swap fails​

  • Signature rejected or expired: sign again. Nothing was spent.
  • Price moved: the output would be below your minimum, so the transaction reverts. Refresh the quote and try again, or raise slippage.
  • Below the minimum or unsupported route: turn gasless mode off and swap normally.

Technical details are in gasless architecture.

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