Optimistic

In optimistic rollups, the operator posts a batch of transactions and the corresponding state root to a base layer.

The system relies on a network of verifier nodes to check the operator’s work. Any verifier can run the transactions and construct the root independently. If it finds that the operator’s root doesn’t match its own, it can submit a fraud proof within a challenge period.

Most proof mechanisms re-execute a subset of the transactions on-chain to determine the correct state root. If this root differs from the operator’s: the root is rolled back, and the operator’s stake is slashed and given to the verifier. If not: the root is kept, and the verifier’s bond is either burned or given to the operator. These economic incentives ensure correct behavior, but it also creates a delay before transaction finality.