Optimism is a Public Benefit Corporation (PBC) that built Optimistic Ethereum (OE) which is an optimistic rollup L2 on Ethereum.
Similarities between Optimism and Arbitrum:
are rollups and store all txs on L1 are optimistic since they use fraud proofs use sequencers for instant 'finality' have generic cross-chain messaging allowing the creation of advanced token bridges support EVM-related tooling, but need specialized extensions Differences:
different fraud proof verification mechanism Optimism OVM 2.0 is EVM equivalent vs. Arbitrum One (post-Nitro) EVM-compatible Optimism uses single round fraud proofs vs. Arbitrum multi-round FPs Optimism is still gated (private whitelist mainnet for previous applicants) vs. Arbitrum public mainnet (permissionless)
Lets dig deeper through contract.
Comments from Enzo
51% attack in Optimistic Rollups can result in theft of funds, whereas in ZK-Rollup it could only allow for the reverting of transactions.