ZK rollups are definitely better than OP rollups. ZK rollups create ZK proofs from L2 execution results, allowing for immediate verification in L1 contracts, making them more secure, and withdrawals from L2 to L1 are very fast. However, OP rollups state "let's assume it's correct, but if you think otherwise, challenge it within 7 days," which means it takes 7 days to withdraw L2 assets to L1. The verification process is also somewhat ambiguous, right? So, in fact, OP rollups are expected to gradually transition to ZK-based solutions in the long term. However, despite ZK rollups being better than OP, many L2s, including Base, choose OP for two reasons. 1. EVM compatibility issues When Ethereum first came out 10 years ago, there was no consideration for ZK. Therefore, converting EVM, that is, smart contracts written in Solidity, into circuits for ZK proofs is extremely difficult and inefficient. Even if you somehow create a ZK rollup, the smart contracts of L2 often do not perfectly match Ethereum's code. Since achieving 100% EVM compatibility with ZK rollups is very difficult and expensive, L2s tend to choose OP rollups. 2. Cost issues Creating ZK proofs is very expensive. The proofs from the rollup need to be verified on-chain in Ethereum, and the gas fees for this are also high. Moreover, as mentioned in point 1, since EVM itself is not ZK-friendly, it becomes even more expensive. Teams like Succinct and RISC0 are working to reduce proof costs by improving VMs, and companies like @cysic_xyz are creating ZK-specific ASIC devices, but it is still more expensive compared to OP rollups, which only require rolling up to a Blob. Nevertheless, it is clear that OP rollups need to transition to ZK rollups in the long term, considering the 7-day withdrawal time and trustless verification.