Track 4 · Across chains, and who keeps it honest2 of 4
Cross-chain calls
A contract on one chain can call a contract on another, relayed and verified by the validator network, with the result delivered back. No bridge.
Cross-chain swaps move tokens between chains. Cross-chain calls move logic: a contract on Bitcoin can invoke a method on a contract on Dogecoin and act on the answer, with no bridge required and no requirement that either contract trust the other.
How it works
The calling contract emits a request naming the target chain, contract, method, and arguments. The validator network relays it to the target chain, where the method runs as its own transaction. The outcome (success and any return value, or a clean failure) is carried back and handed to a callback method on the original contract. Every leg is a normal, public, replayable action.
Asynchronous, not a remote function call
This is messaging between contracts, not an instant function that blocks and returns a value mid-run. The call and its result are separate on-chain steps that each wait for their own chain's blocks, and your contract resumes when the result arrives. Designing for that (fire the call, handle the answer in a callback) is the whole model.
Secured by the validator quorum
No single relayer is trusted. A two-thirds-plus (2f+1) quorum of staked validators must independently agree on both the call and its result before either is acted on, and each agreement is signed and checked on-chain. A faulty or dishonest validator can be outvoted but cannot forge a call or fake a result.
No bridge, no custody
The validators coordinate the message; they never take custody of funds, and nothing is wrapped or locked-and-minted. If a call moves value, it does so through the same escrow rails as everything else on XChain. The bridge risk that has drained other cross-chain systems simply isn't here.
What you can build
A contract that reads or triggers state on another chain: a token on Litecoin that mints only when a Bitcoin contract says so, a multi-chain registry kept in sync, or any workflow that needs one chain's contract to act on another's. Combined with real-world data, contracts can react to events well beyond their home chain.