All terms
A rollup that assumes transactions are valid unless someone proves otherwise.
Optimistic rollups post results and open a challenge window, typically seven days. Anyone can submit a fraud proof during that period to reverse an invalid batch.
The tradeoff is withdrawal time. Moving funds back to layer 1 through the official route means waiting out that window, though bridges offer instant exits for a fee.
Arbitrum, Base, OP Mainnet and Blast are all optimistic rollups.
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