Flashbots is a research and development organization that builds tools and studies the effects of maximal extractable value (MEV). On proof-of-stake Ethereum, its best-known project is MEV-Boost: optional open-source middleware that validators can run to connect to a market of independent block builders through relays. It supports proposer-builder separation outside Ethereum’s core protocol; it does not eliminate MEV or mean that Flashbots itself builds every block.
How MEV-Boost Fits Together
Block builders assemble candidate blocks and compete to offer a payment to the validator proposing the next block. Relays sit between builders and validators: they check and route block bids, then make a bid available to a proposer. MEV-Boost queries the relays configured by a validator and returns a suitable bid for the validator to consider.
The roles are separate. A validator proposes and attests to blocks, a builder constructs a candidate block, and a relay provides a trusted communication and data-availability layer between them. MEV-Boost is software connecting those roles; it is not itself a builder, relay, or consensus rule.
Other Flashbots Tools
Flashbots also develops tools for searchers and users. Flashbots Protect is a transaction-submission service intended to reduce some risks associated with public transaction broadcasting. MEV-Share is a separate open protocol that lets users, wallets, and applications selectively share transaction information with searchers and define how bids can be distributed. These serve different purposes from validator-facing MEV-Boost.
Tradeoffs and Criticism
- MEV continues: MEV-Boost changes how block space is built and sold; it does not prevent all transaction reordering, arbitrage, or other forms of MEV.
- Relay trust: relays handle block delivery and checks, creating trust and availability assumptions. Validators can configure relays, but that choice and the set of available builders can affect censorship resistance and reliability.
- Market concentration: if block building or relay services are concentrated among a small number of operators, the system can create coordination or censorship risks. MEV-Boost does not guarantee a decentralized market.
- Different actors, different policies: Flashbots is one organization in a broader ecosystem. Builders, relays, validators, wallet providers, and other software projects have separate operators and policies.
MEV-Boost is best understood as one implementation of out-of-protocol proposer-builder separation. Its effects depend on who runs builders and relays, how validators configure them, and how the market changes over time.
Social Media Sentiment
A September 2022 r/ethstaker discussion comparing MEV-Boost relays raised concerns about censorship and trust in relay operators, while participants also discussed connecting to multiple relays to reduce dependence on one. The thread is historical: relay policies, participants, and Ethereum’s block-building market have changed since then. It shows a recurring governance concern, not a current ranking of relays.
Last updated: 2026-10
Related Terms
See Also
- What Is MEV—and Why Every Ethereum Transaction Is a Game
- Is Ethereum Staking Making the Network More Centralized?
- Are Layer 2 Networks Actually Decentralized?
- Swap crypto with ChangeNOW
Sources
- Flashbots Docs — organization and project overview — Describes Flashbots as an MEV research and development organization and links its current tools for users, searchers, validators, builders, and relays.
- Flashbots Docs — MEV-Boost overview — Explains how validator-run middleware connects to builders and relays to provide an out-of-protocol block-building market on proof-of-stake Ethereum.
- Flashbots Docs — relay fundamentals — Details relay responsibilities and the trust, block-validity, and data-availability assumptions between builders and proposers.