Preconfirmation
A preconfirmation (preconf) is a promise from a block proposer to include a specific transaction in an upcoming block at a specific position, issued before the block is actually proposed on-chain. Preconfirmations provide users with immediate transaction finality — they know their trade will execute and at what position — eliminating the uncertainty of the mempool waiting period. Based preconfs are issued by the next proposer in the lookahead window and are economically secured by proposer slashing if they violate the promise. Preconfirmations enable low-latency DeFi applications (sub-block-time user experiences) and reduce MEV risk by removing the window during which a user's transaction can be observed and front-run in the mempool. Preconfs are a key component of Ethereum's based rollup roadmap and are being actively developed by teams like Chainbound and Primev.