Sequencer
The rollup component that decides the order of incoming transactions and posts them as compressed batches to the base chain.
Most Layer-2s today run a single sequencer operated by the team behind the rollup. It gives users near-instant confirmations and very low fees, because it batches thousands of transactions before settling on Ethereum. The flip side is centralization. One operator can reorder transactions for profit or censor specific addresses, and if it goes offline the chain stalls.
The base layer still enforces correctness through proofs, so a sequencer cannot steal funds outright. But the soft powers are real. Projects like Arbitrum and Optimism have published roadmaps toward decentralized, rotating sequencer sets, though most had not shipped them by 2026.
Related terms
A scaling method that batches many transactions off-chain and posts a compressed proof or record to the base layer.
Optimistic RollupA rollup that assumes transaction batches are valid and lets anyone challenge fraud within a set dispute window.
Maximal Extractable Value (MEV)Profit that block producers can capture by choosing how to order or insert transactions within the blocks they build.
Layer 2A separate network built on top of a base chain to process transactions faster and far more cheaply.