Proposer-Builder Separation (PBS)
Proposer-Builder Separation (PBS) is an Ethereum protocol design that splits the block production role into two distinct actors: block builders who construct blocks with optimal transaction ordering, and block proposers (validators) who select among competing blocks without seeing their contents in advance. The separation prevents validators from engaging in sophisticated MEV extraction themselves, which would advantage large, well-resourced staking operations and centralize the validator set. In the current MEV-Boost implementation (a proto-PBS design running on Ethereum before full enshrinement), specialized builders construct execution payloads and bid for inclusion via relays, and validators select the highest-bid block. The builder pays the proposer for inclusion, and this payment flows to stakers as MEV rewards. PBS creates a competitive builder market that reduces MEV centralization risk but introduces new trust assumptions around relay neutrality and builder censorship resistance.