#2 šŸŸ§ How Does Arbitrum Work? Optimistic rollup is a specialized technique for rolling up transactions off-chain. To accelerate the data validation, the optimistic rollup assumes that the transactions in the rollup are valid. Arbitrumā€™s optimistic rollup is executed on top of Arbitrumā€™s rollup chain. Arbitrum collects the transaction batch, settles it on the Arbitrum rollup chain, and then inputs the transaction data back to the Ethereum blockchain.