Crypto glossary
Challenge period (withdrawal delay)
The challenge period is the window, usually about seven days, during which an optimistic rollup's state can be disputed before withdrawals to L1 are final.
Optimistic rollups do not prove their state upfront, so each proposed state root must survive a dispute window before Ethereum treats it as final. On major rollups like Arbitrum One, OP Mainnet and Base that window is around seven days. A withdrawal through the official bridge has to wait for it to pass, after which the user finalises it with a second transaction on Ethereum.
The length is a security choice: it must leave honest challengers enough time to react even if Ethereum is congested or under censorship attempts. In practice most users never wait. Fast bridges and liquidity networks pay out on the destination chain within minutes and later collect the funds from the slow withdrawal, charging a fee for the service.
The delay applies to moving assets from the rollup back to L1, not to deposits or to transactions inside the rollup. It does not exist in the same form on ZK rollups, whose withdrawals wait for a proof instead. Fast bridges replace rollup security with that of their own design, an added risk.
Example
A user withdrawing ETH from Base through the native bridge waits about a week before claiming it on Ethereum, while a friend uses a fast bridge and receives slightly less ETH within minutes.