What Is the Role of a Block Builder in the Private Transaction Process?

In the private transaction process, the block builder (or proposer) is the entity responsible for creating the final block of transactions. When a trader submits a private transaction, it goes directly to the block builder via a dedicated relay, bypassing the public mempool.

The block builder includes this private transaction in the block they are constructing, ensuring it is executed without being visible to front-running bots. The block builder is incentivized by the fee paid by the trader, which replaces the MEV profit that would otherwise go to a malicious searcher.