Why Cross-Chain Swap Prices Diverge When Arbitrage Lags

Cross-chain swap prices diverge when the pools or quote states they depend on update at different times, and arbitrage cannot move inventory between them quickly enough to erase the gap. A displayed quote is a route-specific estimate, not a synchronized price across chains. It reflects pool balances, trade size, fees and the state observed when the quote was made.

What makes cross-chain swap quotes differ?

Each automated market maker (AMM) prices a trade against its own pool reserves. In a constant-product pool, for example, a trade changes the ratio between two reserves; the larger the trade relative to pool depth, the more it moves the pool price. Other AMMs use different curves, but the same practical distinction applies: the marginal price at the start of a trade can differ from the average price paid across the whole trade.

Quotes can also describe different routes. One may use a single pool; another may route through multiple pools or chains. Each step can add price impact and fees. Network costs, protocol fees and any quoted slippage allowance affect the amount the user expects to receive. A useful comparison uses the same input amount and output asset, and compares the estimated net output rather than a spot price alone.

A thor swap can involve a different route and execution process from bridging an asset first and trading it on the destination chain. The linked comparison covers that route choice in more detail; the shared point here is that each route has its own costs and timing.

Why does arbitrage take time to close the gap?

Arbitrageurs trade where the expected price difference exceeds the full cost and risk of execution. If an asset is cheaper in one pool and dearer in another, buying in the first and selling in the second can move both pool prices toward each other. But the apparent spread is not the profit. It must cover pool fees, price impact, network fees and the possibility that one leg executes while the other fails or becomes uneconomic.

Cross-chain execution adds separate state changes on separate networks. A trader may need to submit a transaction on one chain, wait for its inclusion or finality, then submit a second transaction elsewhere. The first pool can change before the second leg lands. Confirmation delays, congestion, reorg risk and transaction ordering can all make the quoted spread stale or leave the trader holding an unintended inventory position.

Some routes use a protocol that coordinates swap steps across chains. That changes how the route is executed, but it does not make all chain states update at once. The quote can still age between estimation and execution, and a swap may fail, time out or return less than expected under the route’s rules. Arbitrage is therefore a sequence of risky transactions, not an instantaneous command that synchronizes every pool.

When is a price gap an actionable opportunity?

A gap matters only if a trader can execute both sides at a net gain. The test is the difference between executable outputs after fees and expected price impact, adjusted for execution risk. A price chart or pool ratio can reveal a discrepancy, but it cannot establish that the same trade size can capture it.

• Match the trade size. A small quoted spread may disappear when the intended amount moves a shallow pool.
• Compare net outputs. Include route fees, network costs and any conversion steps in both paths.
• Account for timing. Check when each quote was produced and how long its execution assumptions remain valid.
• Price the failed-leg risk. If one side can settle without the other, include the cost of holding or unwinding the resulting asset.

These checks explain why visible divergence can persist even when arbitrageurs are active. They may be competing to trade the same opportunity, but the remaining spread can be smaller than the cost of moving inventory, or too uncertain to justify the exposure. In some cases, the pools also serve different users or have different liquidity, so there is no single price that every route must match.

What should a trader infer from divergence?

Persistent divergence is evidence that route prices and settlement conditions differ; it is not by itself evidence of a free profit. For a user choosing a route, the relevant figure is the expected amount received for the chosen input, together with the route’s execution conditions. For an arbitrageur, the relevant figure is the net spread that can still be captured after both legs and their failure modes are priced.

Arbitrage tends to narrow gaps when a trade is executable and its expected return compensates for costs and risk. It does not guarantee identical quotes across chains or at every moment. The practical takeaway is to compare complete routes at the same size and treat each quote as a time-bound estimate of execution, not as a universal market price.