Sequencer

A sequencer is the node or set of nodes that collects, orders, and batches transactions on an optimistic or ZK rollup before they're posted to the underlying blockchain. It matters because whoever runs the sequencer decides transaction ordering, which affects fees, speed, and even who can extract value by front-running trades. Most rollups today rely on a single, centralized sequencer run by the project's own team. For example, Arbitrum's sequencer processes transactions in seconds and gives near-instant confirmations, but if it goes down, users can't transact until it's fixed or an escape hatch kicks in. Projects like Espresso and Astria are building shared, decentralized sequencer networks to reduce this single point of control.