based rollup

A based rollup is a rollup that has no sequencer of its own and instead lets the base layer's own block proposers order its transactions. The name comes from being 'based' on the L1 for sequencing: rather than a dedicated L2 sequencer choosing the order and posting batches, anyone building an Ethereum block (the L1 proposer, often via the existing builder market) can include the rollup's transactions and thereby sequence it. The idea was articulated by Justin Drake in 2023 as a way to maximize a rollup's decentralization and liveness.

The appeal is that the rollup inherits Ethereum's liveness and decentralization for free. There is no single sequencer to go offline, to censor, or to capture MEV exclusively, because sequencing is spread across the entire rotating set of L1 proposers and builders — the most decentralized actor set available. It also composes naturally with the L1: because the rollup's transactions are ordered by the same party building the L1 block, atomic cross-domain interactions between the rollup and Ethereum become more tractable, and a whole class of cross-domain MEV is internalized by L1 rather than siphoned off by a separate sequencer.

The trade-offs are real. Handing sequencing to L1 means the rollup's confirmations move at L1's pace — roughly twelve-second slots — so a based rollup cannot natively offer the sub-second soft confirmations a centralized sequencer provides, which is why active research focuses on preconfirmations: L1 proposers opting in to promise fast inclusion ahead of the slot. A based rollup also forgoes the sequencer fee revenue that funds many L2 teams, passing that value to L1 instead. It is best seen as a deliberate choice to trade some performance and revenue for the strongest possible liveness and credibly neutral ordering.