Why Cross-Chain Swap Quotes Change Before Deposit

A cross-chain swap quote changes before deposit because it estimates execution against current liquidity and fees, while the deposit still has to reach the protocol and be processed. The quote is a simulation, not an order that reserves pool balances. A trade or arbitrage transaction can change those balances in the gap between seeing the quote and the swap executing.

On THORChain, for example, a swap between two connected assets passes through two Continuous Liquidity Pools linked by RUNE. Each pool’s asset ratio helps determine the output, and the swap’s size relative to pool depth affects price impact and the liquidity fee. For a fuller comparison of pool fees with bridge and DEX costs, see this analysis of thor swap. The quote gives a useful estimate, but it cannot freeze the state used to calculate it.

What does a cross-chain swap quote calculate?

A cross-chain swap quote simulates a specified input amount, route and destination against the protocol’s available information at that moment. It estimates the output and may itemise fees and expected delays. On THORChain, those costs can include the source-chain transaction fee, the pool’s liquidity fee, an optional affiliate fee and the destination-chain outbound fee.

The pool fee is tied to liquidity demand. A larger swap consumes more of a pool’s available depth, so it can incur greater price impact and a larger liquidity fee. For an asset pair that uses two pools, conditions in either pool can affect the final estimate. A quote therefore reflects more than a token’s displayed spot price: it models the requested trade through the relevant pools and includes applicable costs.

That simulation is still conditional. The quote does not make the deposit, and it does not hold the pool’s balances for the person requesting it. Other swaps can execute before the deposited funds are observed and processed. Arbitrage trades can also rebalance a pool after a swap has changed its asset ratio. Either can move the output from the earlier estimate.

Why can the output change while the deposit is pending?

The source-chain transaction takes time to confirm, and the protocol must observe it before executing the swap. The delay depends on the source blockchain and the protocol’s confirmation and processing steps. During that interval, pool balances, network fees and queue conditions can change.

On THORChain, the size of the swap and the desired execution pace also matter. Streaming Swaps split a trade into smaller sub-swaps over time. This can reduce the price impact of each part and give arbitrageurs time to rebalance pools between executions. It changes the execution path and timing; it does not turn the original quote into a fixed payout.

Distinguish these three amounts when reviewing a quote:

• Input amount: what the source-chain transaction sends, before any applicable source-chain cost.
• Estimated output: the amount calculated from the quoted route and current state.
• Minimum output: the execution limit encoded for the swap, where supported. If execution cannot meet it, the protocol can refund some or all of the input, subject to the applicable network costs.

A changing estimate does not by itself mean the deposited assets have been lost or that the transaction has failed. Check the transaction’s status and the protocol’s tracking information to see whether the inbound transfer was observed, the swap is queued or executing, or a refund was issued. The estimate describes a possible execution; the transaction status describes what happened.

How should you use a quote before sending?

Refresh the quote close to submission and compare the input amount, estimated output, fees and minimum output with the transaction you are about to sign. Confirm that the destination address matches the output chain. If the quoted output has moved outside the range you accept, request a new quote or do not send.

Pay attention to source-chain gas as well as protocol fees. A slow or underpriced inbound transaction can take longer to confirm, widening the gap between the quote and execution. On some routes, the quote also provides an inbound address or transaction details that should be treated as specific to that quote. Follow the interface’s instructions if it expires or supplies updated details; do not reuse stale deposit information.

The useful takeaway is simple: a quote is a time-sensitive estimate, while a minimum-output limit is the execution boundary. Use the estimate to decide whether the route and costs are acceptable. Use the limit, where available, to define when execution should stop and funds should be refunded instead of accepting a worse output.