KoinlyticsMEV-Boost is an open-source sidecar built by Flashbots. It runs alongside every major Ethereum validator client. It implements Proposer-Builder Separation (PBS): validators do not build blocks themselves; they auction the right to build to specialized builders.
The flow
- Searchers submit MEV bundles to builders.
- Builders assemble full blocks (searcher bundles + regular txs) and compete on total value.
- Relays (trusted middlemen) receive built blocks from builders and forward the header to proposers.
- Proposer (validator) signs the header without seeing the full block content (blind signing enforced by the relay).
- Relay reveals block once signature received.
- Validator pockets the winning bid.
Why validators use MEV-Boost
Higher rewards. Solo block production earns ~0.02 ETH per block. MEV-Boost blocks routinely add 0.05-0.5 ETH bid on top. Over a year, this raises validator APR from ~3% to ~3.5-4%.
Adoption
Over 90% of Ethereum validators run MEV-Boost. Non-MEV-Boost validators earn less and would be economically penalized long term.
Concerns
- Relay centralization. A few relays (Flashbots, bloXroute, Ultra Sound) dominate. If a relay censors (drops sanctioned txs), most blocks censor.
- Censorship compliance. Flashbots relay complied with OFAC after Tornado sanctions. Non-censoring alternatives exist (Ultra Sound, Agnostic).
- Builder concentration. Top 3 builders produce most winning blocks.
Native PBS
Ethereum's roadmap includes native PBS (baked into the protocol). Would remove the trusted relay layer. Not shipped as of 2026, but active research.