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What is proposer-builder separation?
Proposer-builder separation (PBS) splits Ethereum block production into two jobs: specialized builders assemble blocks and bid to have them used, and the validator chosen as proposer picks the most profitable bid. An arrangement like this runs outside the protocol today; building it into the protocol is still research.
What it means for you
It shapes which transactions get in and in what order. Builders compete to profit from transaction ordering, which is how a swap with loose slippage settings can be sandwiched; and if a few builders dominate, they could leave certain transactions out, which the proposed inclusion lists are designed to counter.
How it works
Under PBS the proposer does not see a block's contents; it accepts the block whose builder pays the highest bid. The aim is to keep validating simple enough for ordinary stakers while specialized builders handle the work of extracting MEV, spreading that value across many validators instead of concentrating it. Censorship is harder because a builder that wants to exclude a transaction must outbid every builder that does not. Today validators can outsource building to builders through intermediaries called relays; an in-protocol version has no final specification yet.
Sources: ethereum.org: Proposer-builder separation, ethereum.org: Maximal extractable value (MEV) · checked 4 October 2026
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