What Is the Difference between a Block Proposer and a Block Builder in Ethereum’s PoS?

In Ethereum's Proposer-Builder Separation (PBS) model, the "block proposer" is the validator randomly selected to propose the next block, earning the priority fee. The "block builder" is a specialized entity that receives transaction bundles from searchers, constructs the optimal, most profitable block payload, and submits it to the proposer.

The proposer then signs the block header from the builder, separating the block construction logic from the proposer's role.