Based Sequencing
Based sequencing is a rollup design pattern where the Layer 1 (Ethereum) validators are the sequencers for the rollup, rather than a centralized sequencer controlled by the rollup team. In a based rollup, transactions are submitted to L1 validators who include them directly in L1 blocks in the order they arrive. This shifts sequencing authority from the rollup operator to the decentralized L1 validator set, reducing liveness and censorship risks. Based sequencing enables synchronous composability between rollups — transactions on two based rollups can be atomically included in the same L1 block, enabling cross-rollup arbitrage and MEV. The tradeoff is that based rollups inherit L1 block times (~12 seconds) rather than providing the sub-second confirmations of a centralized sequencer. Preconfirmations solve this by letting the next proposer issue fast off-chain guarantees.