Glossary
MEV-Boost
The out-of-protocol implementation of proposer-builder separation on Ethereum — a sidecar that lets validators sell their block space to competing builders.
MEV-Boost runs alongside a validator's consensus client. Before each block, it requests sealed header bids from a set of "relays"; each header is built by a builder. The validator signs whichever header pays them the most, and the relay then reveals the body for inclusion.
Adoption has been near-universal among Ethereum validators since launch: it pays better than self-building and is easy to run. The trade-off is that a small number of builders (and the relays that deliver them) now produce most blocks, raising centralization concerns.