What is Rollup Rollup is a technology for scaling Ethereum that "rolls up" a large amount of computation and data off the main chain, only submitting key data on-chain, thereby increasing speed and reducing costs. ➣ Optimistic Rollup ▰ "Optimistically" assumes that off-chain transactions are correct ▰ Sets a challenge period for each submitted block (usually 7 days) ▰ During this period, anyone can submit a "fraud proof" to challenge incorrect transactions Advantages: Simple computation, easy to implement Disadvantages: Long withdrawal waiting time (because it has to wait for the challenge period) Representative projects: Arbitrum, Optimism ➣ ZK Rollup ▰ Generates zero-knowledge proofs when packaging transactions to prove their correctness ▰ No challenge period is needed; the main chain can verify this proof to confirm the transaction's validity Advantages: Secure, fast withdrawals Disadvantages: ZK proof computation is complex, high development costs Representative projects: zkSync, Starknet, Scroll ➣ Hybrid Rollup ▰ Combines the advantages of both Optimistic and ZK methods ▰ In design, it may first use the optimistic mechanism for quick execution, then asynchronously verify through ZK proofs, or support switching between the two verification methods Goal: Balance performance, security, and development flexibility Representative projects: Fuel V2, Taiko (proposed to adopt hybrid verification)