With the merge and the change to PoS, there will also be a shift towards PBS. As far as i have researched, any block builder can build blocks with transactions from the mempool.

How are these blocks then offered to the validators to be included? I have found mev-boost which can be run by a validator to select mev-optimized blocks from a certain relay, however i am wondering how this happens by default. How and where do block builders send their built blocks and from where do validators select a block to be proposed by default?

Are there any standard relays or is the consensus client offering functionalities to broadcast possible blocks from which validators can choose?

1 Answer 1


There is no proposer builder separation (PBS) right now on the beacon chain on Ethereum. After the merge, there still will not be any proposer builder separation built-in the protocol. Proposers, which are going to be the validators, will default to building block using a simple algorithm to maximize their tips from the transactions they can see in the mempool.

Any validator who wants to profit from MEV or get that additional MEV reward can install mev-boost to get access to blocks being externally built from a third party.

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Searchers can implement strategies to extract MEV, pass their findings to a builder that will announce the block through a relay that will ask a validator that is selected for proposing an upcoming block to sign and include it in the chain. This will be the main mecanism through which searchers can have their block accepted on the network after the merge.

You can learn more about this on Flashbots and on the Builder specs.

Flashbots will be offering a relay but other company like bloXroute already have their relay offering prepared for Mainnet.

  • Thank you for the detailed answer! I suppose free builders will generally be at a disadvantage to relay operators due to not having access to (more / all) high value mev txs. I am wondering, whether there are settings available as part of mev-boost to influence block selection to not always go for the block with the highest value (probably among all the relays which are consumed).
    – Plus Ultra
    Commented Aug 30, 2022 at 13:21
  • 1
    @PlusUltra This tweet asks for those "settings" to be built and someone might reply with what they've built.
    – eth
    Commented Nov 27, 2022 at 12:47

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