Optimistic Rollup
A rollup that assumes transaction batches are valid and lets anyone challenge fraud within a set dispute window.
Optimistic rollups assume every batch is honest until proven otherwise. They post transaction data to Ethereum without a validity proof, trusting watchers to flag bad ones. Arbitrum and Optimism are the largest.
That trust has a cost. To allow challenges, withdrawals to Ethereum carry a dispute window, traditionally seven days. Want out faster? Pay a third party for an instant exit through a liquidity bridge.
They are cheaper and simpler to build than zk-rollups, which is why they captured most early Layer 2 activity.
Related terms
A scaling method that batches many transactions off-chain and posts a compressed proof or record to the base layer.
zk-RollupA rollup that posts a cryptographic validity proof for every batch, giving near-instant finality on the base chain.
Layer 2A separate network built on top of a base chain to process transactions faster and far more cheaply.
BridgeA protocol that moves tokens or data between two separate blockchains that cannot otherwise talk to each other.