MEV is Maximal Extractable Value. It is the profit a block proposer (miner or validator) can make through their ability to arbitrarily include, exclude, or re-order transactions from the blocks they propose.

Read Maximal Extractable Value in the Ethereum docs.

You should run mev-boost to earn a fair share of the MEV extracted in the blocks you propose. Connecting your consensus client to mev-boost allows you to get full blocks from a network of block builders optimized for MEV extraction.

Read Why run mev-boost? and MEV in eth2 - an early exploration.

Yes. The initial Audit Report for mev-boost can be found here:

Yes. mev-boost is designed to be used by any validator, no matter the size of its stake.

In Ethereum proof-of-work we had no way to prevent small miners from misbehaving and stealing MEV. Once identified, they could just get a new identity and continue misbehaving. The solution was to make a list of allowed miners that were big enough to be concerned about their reputation. Their profit would be severely affected if they were removed from the allowed list. This resulted in one more incentive for the concentration of mining power in a few organizations.

The most significant change for MEV in Ethereum proof-of-stake is that with mev-boost now validators can be permissionless. The order is reversed: instead of the Flashbots relay sending blocks or bundles of transactions to the miners, now the validators request blocks to the Flashbots relay through mev-boost. The Flashbots relay in turn requests blocks to a network of builders and gives the header of the most profitable one to the validator, while holding the payload in escrow. Once the validator signs the header, the relay sends the block payload to the proposer. If at this moment the validator decides to propose a different block, they will have signed two blocks and will be slashed.

Note that this does not mean that the system is fully permissionless and decentralized, yet. The Flashbots relay is still trusted.

Read the open research questions and join us exploring possible solutions.

Block building is a new role introduced by proposer-builder separation (PBS). Using MEV-Boost, validators can sell blockspace to specialized third parties called block builders who collect and sequence transactions to produce a block. Block builders want to produce a block that maximizes the fees collected in the form of priority fees and MEV.

Block builders must connect to a MEV-Boost relay in order to submit their payloads to validators for inclusion. Each relay may have different rules and provide access to different validators.

While we expect there will be several relays at the merge, block builders must be careful who they submit their payloads to. A relay has the power to censor or frontrun any block proposed by a block builder.

The Flashbots Relay (relay.flashbots.net) will start accepting block proposals from any block builder and continue our policy of neutrality and transparency. Documentation on the Flashbots Relay will be released closer to the merge.

Our relay will publish the logs of when blocks were received by builders and when they were supplied to proposers.

We expect several relay monitoring dashboards to emerge which keep track of relay performance and help block builders and validators to select a relay.

→ Relay API Documentation (draft)

Slot collisions occur when more that one relay delivers a payload for a given slot. Multiple builders build blocks for a given slot, and these blocks can be submitted to multiple relays. If a block is the most profitable block for multiple relays at a given slot, it is possible each of these relays would return the block during a getHeader request for the same slot.

High/low builder prioritization works the same way it does for Flashbots searchers, which is to say that low/high priority get different simulation clusters and in times of high load, such that high-priority builders will be prioritized over low-priority builders. Reputation is just a mechanism to help mitigate DDOS attacks, but doesn't affect how Flashbots scores blocks.