🟪 #1 Optimistic Rollup Arbitrum relies on the Optimistic Rollup technology (used to scale Ethereum). A bundle of transactions from L2 (Arbitrum) is formed into a batch and sent to L1 (Ethereum), where it is then approved by validators. Batch sending and validation are designed so that Ethereum nodes are not executing every L2 transaction as in the case of L1, so throughput is much higher and transactions are cheaper.