Sequencer

A sequencer orders and batches transactions on a rollup before posting them to Layer 1, playing a critical role in determining transaction inclusion, ordering, and timing. Currently, most rollups operate with centralized sequencers run by the core team, Arbitrum's is run by Offchain Labs, Optimism's by the Optimism Foundation. This centralization creates several concerns: censorship risk (the sequencer could refuse to include certain transactions), MEV extraction (the sequencer can reorder transactions to extract value), and liveness risk (if the sequencer goes down, the rollup halts). Rollups typically have escape hatches allowing users to force-include transactions through L1, but this is slow and expensive. Sequencer decentralization is a major priority for rollup roadmaps. Approaches include rotating sequencer sets, leader election among staked operators, and shared sequencers that order transactions across multiple rollups. Shared sequencing could enable atomic cross-rollup transactions and reduce fragmentation. The sequencer revenue model matters too: sequencers earn fees and MEV, creating valuable property rights. How this revenue is distributed (to token holders, stakers, or public goods) shapes rollup economics. Sequencer decentralization is one of the most important open problems in rollup design.