Who Controls Ethereum Blocks and Why Vitalik Wants to Change It
Every time you make a transaction on Ethereum, it sits in a public waiting room - called the mempool. Specialized entities known as - Ethereum block builders - then assemble candidate blocks for their blockchain by selecting and ordering transactions from it before the next Ethereum block is proposed.
Most users never think about this. But this invisible layer of control has quietly become one of Ethereum's biggest structural debates. Vitalik Buterin has been vocal about improving how block production works, and his proposals aim to move more of this process from private infrastructure into Ethereum’s core protocol.
Key Takeaways
- Validators propose each Ethereum block, but often rely on specialized Ethereum block builders to construct them.
- MEV Ethereum opportunities allow profit through transaction ordering.
- A small number of builders currently produce a large share of Ethereum blocks.
- Vitalik Buterin’s ePBS proposal would bring proposer-builder separation into Ethereum's protocol.
- FOCIL aims to reduce censorship risks by ensuring certain transactions cannot be ignored.
How Block Building Works Today
Validators are responsible for proposing blocks on Ethereum. But most validators today do not build the Ethereum block themselves. Instead, they outsource that job to Ethereum block builders through a system called MEV-Boost.
Builders scan the mempool, order transactions for maximum profit, and submit finished blocks to validators through relays. Validators then pick the highest-paying block and sign off on it.
This system emerged because extracting MEV Ethereum opportunities requires specialized infrastructure and strategies that many validators do not run themselves. But it has also created a concentration problem.
Ethereum has hundreds of thousands of validators, yet a relatively small number of Ethereum block builders often construct a large share of blocks.
What MEV Is and Why It Costs You Money
MEV stands for Maximal Extractable Value . In the context of MEV Ethereum, it refers to the profit builders extract by controlling the order of transactions inside an Ethereum block.
The most common example is the sandwich attack. A bot spots your token swap in the mempool, places a buy order just before it and a sell order just after, and profits from the price movement your trade caused. You get a worse price. The bot keeps the difference.
MEV Ethereum strategies have extracted billions from Ethereum users since 2020. It is not a bug that gets patched easily. It is a structural outcome of how Ethereum block building currently works.
The Censorship Problem
In 2022, following OFAC sanctions on Tornado Cash, several Ethereum block builders began excluding transactions linked to the sanctioned protocol. At peak, over 70% of Ethereum blocks were OFAC-compliant, meaning they actively filtered out legally disfavored transactions.
Ethereum, built on the promise of censorship resistance, was effectively enforcing US financial regulations at the infrastructure layer. No protocol rule stopped builders from doing this. And if Ethereum block builders can filter transactions for regulatory reasons today, they could theoretically filter them for other reasons tomorrow.
What Vitalik Wants to Change
Vitalik's response centers on two proposals.
- ePBS (Enshrined Proposer Builder Separation)
It would bring the builder and proposer relationship directly into Ethereum's consensus rules. Currently, builders and validators interact through MEV-Boost relays that operate with no protocol-level accountability. ePBS removes that gap and gives the protocol direct oversight over how block construction works.
- FOCIL (Fork Choice Enforced Inclusion Lists)
This is the more direct fix for censorship. A rotating committee of validators would maintain a list of transactions that builders must include in the next block. Builders can still optimize for profit, but skipping a listed transaction means the network can reject the block outright.
Together, the proposals aim to separate two powers the current system bundles together: the right to build an Ethereum block and the power to censor one.
Bottom Line
Ethereum’s neutrality promise holds at the consensus layer. But the rise of specialized Ethereum block builders means that transaction ordering increasingly happens through a small set of infrastructure providers.
Vitalik Buterin’s push for ePBS and FOCIL aims to move more of that system into the protocol itself and ensure Ethereum’s censorship resistance holds even as Ethereum block production becomes more specialized.
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FAQs
- What is MEV, and how does it affect regular Ethereum users?
MEV Ethereum refers to the profit extracted by Ethereum block builders through controlling transaction order inside an Ethereum block. It appears that strategies like sandwich attacks and front-running often give users worse execution prices on swaps. - Is Proposer Builder Separation already live on Ethereum?
A version exists through MEV-Boost, but it runs off-chain with no protocol oversight. Vitalik's ePBS proposal would bring it directly into Ethereum's consensus rules. - What is FOCIL, and how would it prevent censorship?
FOCIL requires builders to include transactions flagged by a validator committee. If a builder ignores those transactions, the network could reject that Ethereum block. - When will ePBS or FOCIL go live on the Ethereum mainnet?
Both are still in the research phase with no confirmed upgrade timeline. Mainnet implementation is likely still a few years away.