Before the merge, mev-relay (commonly referred to as “the relay”) was responsible for accepting bundles from searchers and relaying them to miners.
After the merge, the term “relay” will mean something entirely different. These relays are a component of PBS – they’re responsible for escrowing blocks from builders for validators. With mev-boost, validators choose the most profitable block from a number of relays. Each relay keeps the contents of a block private until the validator commits to proposing it to the network for inclusion.
Specifically, relays do the following:
- accept new blocks from builders
- send header of most profitable block to a validator upon request
- the validator locks in their commitment to propose the full block by signing this header
- send full block to validator after receiving block header signed by the validator
- perform all of this quickly and reliably, so that validators don’t miss proposal deadlines
For more information about how bundles are sent post-merge, see this forum post.