Crypto glossary
Based rollup
A based rollup lets Ethereum's own block proposers order its transactions instead of running a separate sequencer, inheriting L1 liveness and neutrality.
In a based rollup, also called L1-sequenced, there is no dedicated sequencer. Anyone can publish rollup blocks, and the Ethereum proposer, helped by block builders, decides which ones are included and in what order. The rollup's ordering therefore inherits Ethereum's decentralisation and censorship resistance directly.
The idea gained momentum because it removes the single-operator weak point that most rollups share, and because based rollups can, in principle, compose synchronously with Ethereum and with each other. Taiko was the first prominent rollup on mainnet to adopt the model, and research on based sequencing has become a central topic in Ethereum's rollup roadmap.
Two costs explain why it is not the default. Block times follow Ethereum's 12-second slots unless the system adds preconfirmations, and most MEV flows to L1 proposers rather than to the rollup, removing a large revenue source. Being based also says nothing about how the rollup proves its state; a based rollup can still lack mature proofs.
Example
A team launches a based rollup so that no company can censor its users, then integrates preconfirmations from Ethereum proposers to give wallets sub-second feedback instead of waiting a full slot.