Source Chain Reorganizations for Bridge Beginners

A source-chain reorganization can delay or erase a pending bridge deposit, though the destination transfer may already be complete if a relayer filled it first. The exact result depends on whether the source deposit remains in the chain’s accepted history.

A reorganization can remove a deposit before it is settled

A source chain is where your transfer starts; the destination chain is where the tokens should arrive. A block is a batch of recorded transactions, and a reorganization, or “reorg,” happens when the network replaces a recent block with another one.

  • A transaction can look confirmed, then disappear from the accepted chain history.
  • A relayer may send destination tokens before the source deposit is fully settled.
  • The protocol checks deposits later before repaying relayers.
  • Your next step is to check both the source transaction and bridge status.

For example, the acrossbridge service can have a relayer send tokens to your destination address before the source deposit has completed settlement. A quick arrival is useful, but it does not prove the source block is final.

A relayer is a service that pays out tokens on the destination chain using its own funds. Across uses this fast fill approach, then checks the deposit during later settlement. That gives speed, while leaving the relayer exposed if the source transaction vanishes.

The source deposit decides whether the transfer counts

If a reorg removes the block containing your deposit, the deposit may no longer count as a valid source-chain event. A later check can then reject repayment to the relayer because there is no valid deposit to match its payout.

Say you send 100 tokens and a relayer delivers the agreed destination amount. If the source block is replaced before the deposit is secure, the relayer may have paid out without a valid deposit behind it. In Across, the relayer bears this finality risk; “finality” means the point when a transaction is treated as settled and extremely unlikely to be reversed.

This is different from a slow destination transfer. A pending status can mean the relayer has not filled yet, while a filled status means tokens were sent on the destination chain. A reorg can make the source side uncertain even after that destination fill.

For acrossbridge users, the practical point is that speed and source-chain certainty are separate. A reorg may delay a fill while relayers wait for stronger confirmation, or challenge settlement after a fast fill. The exact wait depends on the source chain and its reorg risk.

Check the source transaction before trying again

Use the transaction hash, the transaction’s unique reference, to check whether your source transfer remains in the chain’s current history. Then check the bridge’s deposit status and destination transaction; these show whether it is still pending, filled, or refunded.

If the source transaction is missing or marked dropped, do not immediately send another transfer. First check your wallet balance and the bridge status: the original transaction may return to your balance, or it may be included again. A second send could create a second deposit.

Across transfers use relayers for fast delivery, then verify deposits during settlement. When tracking acrossbridge, check source and destination records separately, since one can update before the other.

Before acting, ask yourself: have I confirmed what happened to the original source transaction, or am I about to send it twice?

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