Cross-chain swaps

Cross-chain routes combine a bridge with optional swaps on either side. XAUConnect aggregates the 0x Cross-Chain API with a 1inch Fusion+ fallback and returns a composite quote so you can judge the route by the net amount received on the destination chain, not the headline rate on the source side.

1. POST /swap/cross-chain/quote — requires fromChainKey, toChainKey, tokens, amountIn, and taker
2. POST /swap/cross-chain/build — returns the origin transaction plus executionSteps[]
3. Sign and broadcast the origin transaction on the source chain
4. GET /swap/cross-chain/status/:quoteId — poll until the destination settles

1. Quote

POST /api/swap/cross-chain/quote
{
  "fromChainKey": "ethereum",
  "toChainKey":   "base",
  "tokenIn":  "0xA0b8...",   // USDC on Ethereum
  "tokenOut": "0x8335...",   // USDC on Base
  "amountIn": "100000000",   // 100 USDC (base units)
  "taker": "0xYourWallet"
}

If fromChainKey === toChainKey the API returns SAME_CHAIN — use the same-chain /swap/quote instead. If no bridge route exists you get NO_CROSS_CHAIN_ROUTE (HTTP 503).

2. Build

Pass the original request and the returned quote. The response includes the origin-chain transaction and an executionSteps[] array — composite routes (swap → bridge → swap) may require more than one wallet transaction, so always iterate the steps rather than assuming a single signature.

POST /api/swap/cross-chain/build
{ "request": { ...the quote request... }, "quote": { ...the returned quote... } }

3. Sign & broadcast

Sign the origin transaction with the user's wallet on fromChainKey and broadcast it. Keep native gas on both chains — source gas to initiate the bridge, destination gas for any follow-up swap or transfer.

4. Poll status

GET /api/swap/cross-chain/status/{quoteId}?originChainKey=ethereum&originTxHash=0x...&toChainKey=base

Poll every few seconds until the status reports settlement on the destination chain. Most configured routes finalize within a few minutes up to roughly fifteen. Never submit a second bridge while the first is in flight unless the interface clearly reports failure — duplicate bridges are a common, costly mistake.

Notes for agents

• Solana ⇄ EVM routes cross address-format boundaries — validate destination wallet format before signing.
• The token that arrives may be a bridged/wrapped representation with a different contract and decimals.
• Bridges carry smart-contract risk on top of swap risk; test unfamiliar routes with a small amount first.