MEV-Boost is the piece of software that fundamentally changed how Ethereum blocks are built after the Merge. Before MEV-Boost, Ethereum validators built their own blocks — but sophisticated actors could run “searcher” bots that detected profitable opportunities (arbitrage, sandwich attacks, liquidations) and paid high gas to get their transactions included favorably. The MEV (Maximal Extractable Value) that validators could capture was limited by their own block-building sophistication. MEV-Boost unbundled block building from block proposing: validators plug in MEV-Boost and receive sealed bids from specialized block builders; the highest bidder’s block gets proposed; the validator receives the bid payment (MEV rewards) while the builder keeps MEV profits not captured in their bid. This single piece of software, adopted by 90%+ of Ethereum validators within months, reshaped Ethereum’s economic architecture and is central to understanding how Ethereum’s fee market actually works.
Background: The MEV Problem
MEV (Maximal Extractable Value):
Value that can be extracted from blockchain users by controlling transaction ordering.
Types:
- Arbitrage: Profit from price differences between DEXes; harmless to users
- Sandwich attacks: Front-run a user’s DEX trade then back-run it; user gets worse price
- Liquidations: Bots race to liquidate undercollateralized DeFi positions; competitive but necessary
- JIT (Just-In-Time) Liquidity: Add then remove liquidity in same block around a trade
- NFT sniping: Front-run valuable NFT trait reveals
Pre-Merge MEV problem:
- Miners ordered transactions; searchers paid high gas for favorable inclusion
- Gas price spike of “gas wars” → everyone overpays; network congestion
- MEV extraction often adversarial to regular users (sandwiching)
- Miners who ran their own searchers extracted MEV unfairly
Flashbots’ solution (pre-Merge):
MEV-Geth modified the mining software to accept off-chain “bundles” — packages of ordered transactions with payment. Searchers sent bundles via private mempool; miners accepted best bid. This was the precursor to MEV-Boost.
Proposer-Builder Separation (PBS)
The core insight: Block building (deciding which transactions to include and in what order) and block proposing (signing the block and attesting) require different skill sets.
Without PBS (pre-MEV-Boost):
- Validator does both: builds their own block + proposes it
- Must run sophisticated MEV software to capture full value
- Individual validators with small stake cannot compete with specialized block-builders
With PBS (MEV-Boost):
- Builders compete to construct the most valuable block
- Relay (neutral middleware) audits builder blocks and runs the auction
- Validator accepts the highest bid from relays via MEV-Boost
- Validator signs and proposes the block; receives bid payment
- Builder keeps MEV in excess of their winning bid
How MEV-Boost Works
The following sections cover this in detail.
The Flow
“`
[Ethereum Mempool] + [Private order flow]
↓
[Builders] (Flashbots, BeaverBuild, Titan, Rsync, etc.)
Each builds an optimized block; submits “execution payload header” + bid
↓
[Relay] (Flashbots Relay, BloXroute, Agnostic, Manifold, Ultra Sound)
Audits blocks for validity; runs auction; serves winning header
↓
[Validator + MEV-Boost]
Requests headers; picks highest bid; signs blind header
↓
[Relay releases full payload + Validator reveals signature]
↓
[Ethereum network attests to the block]
“`
Trusted Relay Requirement
The relay is a trusted intermediary: It must:
- Verify builder blocks are valid (no invalid txns, correct state root)
- Not reveal the block content until the validator commits
- Not cheat the validator by withholding a better bid after commitment
Current relay trust assumption: Validators trust relays to run honestly. This “trusted relay” is the main critique of MEV-Boost — it introduces a centralized trusted party. Enshrined PBS (ePBS) — a future Ethereum upgrade — would remove the relay trust assumption.
Block Builder Concentration
MEV-Boost has created a concentrated block building market:
Top builders by block share (approximate):
- BeaverBuild: ~25–40% of blocks
- Flashbots: 20–30%
- Titan Builder: 10–20%
- rsync-builder: ~10%
- Others: remainder
Why concentration?
- Block building is winner-take-all: the builder who can capture the most MEV per block wins the auction
- Private order flow deals: trading firms (market makers, hedge funds) send transactions directly to specific builders bypassing the mempool
- PFOF (Payment for Order Flow): Builders pay for exclusive access to order flow → more MEV extraction per block → higher bids → more validator selection
Concern: If 2–3 builders build >50% of blocks, they have significant influence over transaction inclusion across the entire Ethereum network.
MEV Redistribution and SUAVE
Ethereum’s MEV supply chain currently flows:
User → Builder (MEV extraction) → Validator (MEV reward via bid)
SUAVE (Single Unifying Auction for Value Expression):
Flashbots’ next-generation design to:
- Decentralize the block building process
- Create a permissionless MEV market
- Return MEV to users through order flow auctions (OFAs)
The goal: rather than extracting MEV from users, create a system where users can capture their own MEV value by selling their order flow to the highest bidder (getting better prices than the DEX would give them).
MEV-Boost and Validator Revenue
MEV-Boost significantly increases Ethereum validator revenue:
Pre-EIP-1559 base fee era: Validators received gas fees; MEV-Boost adds MEV tips on top.
Validator income sources:
- Consensus rewards (fixed, from ETH issuance)
- Priority fees (EIP-1559 tips to validators)
- MEV-Boost bids (from block builders)
The MEV-Boost income component is highly variable:
- Average blocks: small tips
- “Hot” blocks (e.g., major NFT drop, liquidation cascade): validators can earn 10–100x average via MEV-Boost for a single block
Impact on staking economics: MEV-Boost income is one reason liquid staking tokens (stETH, rETH) have higher APRs than naive calculations suggest — they capture MEV rewards across all validators.
Path to Enshrined PBS (ePBS)
MEV-Boost solves the builder/proposer separation problem but with a trusted relay. The Ethereum roadmap includes “enshrined PBS” that would:
- Implement PBS at the Ethereum protocol level
- Remove the relay trust requirement
- Likely combined with attester-proposer separation (APS) — further separating who can propose and attest
EIP-7547 (Inclusion Lists): Validators can add a list of transactions the builder must include, preventing full censorship even in the PBS model.
Social Media Sentiment
MEV-Boost is simultaneously one of the most successful pieces of Ethereum infrastructure ever shipped and one of the most criticized. MEV-Boost increased validator returns (good for staking economics) and brought structure to MEV extraction (reducing gas wars that congested the network). But the centralization of block building and the trusted relay requirement are real concerns. The “PFOF” dynamic in block building — where large trading firms get preferential order routing — is seen as a form of crypto market structure that mirrors the worst parts of traditional finance. The debate between “MEV is natural market efficiency” and “MEV extraction is stealing from users” continues. The long-term trajectory (SUAVE, ePBS, inclusion lists) points toward more decentralized MEV markets where users capture more value, but the current state heavily favors professional block builders.
Last updated: 2026-04
Related Terms
Sources
Daian, P., Goldfeder, S., Kell, T., Li, Y., Zhao, X., Bentov, I., Breidenbach, L., & Juels, A. (2020). Flash Boys 2.0: Frontrunning in Decentralized Exchanges, Miner Extractable Value, and Consensus Instability. IEEE Security and Privacy.
Flashbots. (2022). MEV-Boost: Merge Ready Flashbots Architecture. Flashbots Documentation.
Yang, S., Nayak, K., & Zhang, F. (2022). Decentralized Block Builder Marketplace: A Model and Analysis. arXiv:2209.00854.
Heimbach, L., & Wattenhofer, R. (2022). Eliminating Sandwich Attacks with the Help of Game Theory. Proceedings of the 2022 ACM CCS Workshop on Decentralized Finance.
Chitra, T., Evans, A., & Kominers, S. D. (2022). A Framework for Single-Item NFT Auctions. arXiv:2209.08345.