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What is an optimistic rollup?
An optimistic rollup is a layer 2 network that assumes the transactions it posts to Ethereum are valid and does not prove them up front. Instead, there is a window in which anyone can challenge a wrong result with a fraud proof, and an Ethereum contract settles the dispute.
What it means for you
Withdrawing straight back to Ethereum means waiting out the challenge period — roughly seven days — before the funds can be claimed on mainnet. Faster exits exist through liquidity providers who pay out at once and charge a fee for it; check that fee and the wait before moving a large amount.
How it works
The operator posts a bond before producing blocks, then submits batches with a claim about the new state. During a challenge period of about seven days, anyone can dispute a claim. Disputes are interactive: the two sides repeatedly split the disputed computation in half until a single execution step remains, which an Ethereum contract evaluates directly, and an operator proven wrong loses its bond. Security assumes at least one honest node is watching. Withdrawals wait out the full period unless a liquidity provider advances the funds for a fee.
An example
Say you withdraw 1,000 of a token from an optimistic rollup to Ethereum. Through the network's own bridge, you can claim it on mainnet about seven days later. A liquidity provider might instead pay you 997 on mainnet within minutes, keeping 3 as its fee and waiting out the period itself.
Source: ethereum.org: Optimistic rollups · checked 4 October 2026
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