What it is
An optimistic rollup is a type of Layer 2 scaling solution for Ethereum that operates on the assumption that all transactions processed off-chain are valid. After transactions are batched and posted to Ethereum, there is a "challenge period" (typically 7 days) during which anyone can submit a "fraud proof" if they detect an invalid transaction. If a fraud is proven, the incorrect transaction is reverted, and the validator who submitted it is penalized.
Optimistic rollups provide significant scalability benefits, enabling much higher transaction throughput than the Ethereum mainnet. Their main drawback is the withdrawal delay due to the challenge period, which can be several days. News often covers the development and adoption of major optimistic rollups like Arbitrum and Optimism, as well as innovations to mitigate withdrawal delays. Retail investors use optimistic rollups for cheaper and faster DeFi and NFT interactions, but must be aware of the withdrawal times.
Why it matters
Optimistic rollups offer fast, cheap transactions on Ethereum but have a delay for withdrawals due to their security model.
Reviewed under editorial standardsUpdated September 26, 2026Not investment advice