🟧 #1 Arbitrum vs. Optimism Arbitrum is not the only Layer 2 blockchain that is a scalability solution on the Ethereum network. It has a main competitor, namely Optimism. Both use optimistic rollup to speed up the transaction process on Ethereum. However, there are some fundamental differences between the two, which are as follows. In solving the problem of incorrect transactions, Arbitrum uses multi-round fraud proofs and is executed off-chain. Meanwhile, Optimism uses single-round fraud proofs. Arbitrum’s multi-round fraud proofs system is more robust, cheaper, and more efficient than Optimism’s single-round fraud proofs system.