Acrossbridge: how a transfer moves between chains

When you submit an Across transfer, you deposit the amount you chose into a contract on the source chain, and a relayer sends the quoted output to your destination address. The transfer is built around a requested result: get a particular token to a particular address on another supported chain.

• You choose the source and destination chains, tokens, amount and recipient.
• A contract records your deposit and transfer instructions on the source chain.
• A relayer pays out the destination funds, then seeks reimbursement through settlement.

What happens when you start an acrossbridge transfer?

You begin by choosing where the funds come from, where they should arrive and how much you want to move. The quote shows the expected output and fees. Check the destination chain and recipient address carefully: a correct amount sent to the wrong address may not be recoverable.

When you confirm, your wallet submits a transaction on the source chain. The deposit goes into a SpokePool, Across’s contract on that chain, along with the details the protocol needs to identify your order. You pay the source chain’s transaction fee, known as gas, as well as any transfer fees shown in the quote.

The phrase acrossbridge captures the key idea: your deposit states the result you want, while the protocol’s participants handle how to fulfil it. You do not need to send a separate message yourself or manually claim the funds on the other chain in the ordinary flow.

How does a relayer deliver funds on the destination chain?

A relayer watches for valid deposits and can send the requested funds to your destination address using its own capital. That is why the visible wait can be short: the relayer advances funds while the protocol’s reimbursement process takes place later.

A relayer is a participant that fulfils transfer requests for a fee. It is not simply forwarding the same coins across a wire between chains. Instead, it pays out on the destination chain against your source-chain deposit, then waits to be repaid under the protocol’s settlement rules.

That distinction explains both the speed and the trade-off. You may receive the destination funds before the source-chain deposit has been fully incorporated into the later accounting process. The relayer is taking on the timing and capital cost, and the fee and quote reflect the terms of the transfer.

How are relayers reimbursed after an acrossbridge transfer?

After a relayer fulfils a deposit, Across records the fill so it can be checked and settled. Its accounting system groups activity across transfers; it does not need to move the user’s funds through the Ethereum pool in real time for every individual payout.

Across’s HubPool, a central liquidity pool on Ethereum, is part of the settlement system. Dataworkers prepare batches of transfer and repayment instructions, and the protocol’s verification process checks the proposed accounting. Once accepted, the relevant contracts can use pooled funds to reimburse relayers.

This later settlement is separate from the user-facing payout. It lets the protocol check the records and handle repayment after the recipient has received funds. It also means the transfer depends on several parts working together: the source-chain contract, a relayer willing to fill the order, destination-chain execution and the settlement process.

What should you check before you send crypto?

Before confirming an acrossbridge transfer, compare the quoted output with the amount you expect to receive. Fees, token conversion and the selected route affect that figure, so the deposit amount is not always the same as the destination amount.

Make sure the token and chain are the ones you intend to use, and review the recipient address. You also need enough of the source chain’s native token to pay gas for the deposit transaction. A quote describes the proposed transfer; it does not remove the need to check what your wallet is being asked to approve.

The practical takeaway is simple: Across separates fast delivery from later repayment. You submit a deposit with instructions, a relayer advances destination funds, and the protocol verifies and settles the relayer’s claim. For you, the important decisions are the route, the quoted output and the exact destination address.