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Optimistic Rollup
A Layer 2 scaling solution that processes transactions off Ethereum mainnet and posts compressed transaction data as calldata or blobs to Ethereum. Unlike zkRollups, optimistic rollups assume transactions are valid by default ('optimistically') and rely on fraud proofs — any validator can challenge an invalid transaction within a 7-day challenge window. Arbitrum One and Optimism are the leading optimistic rollups. Post-Pectra, their blob fees have fallen significantly.
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