Vitalik Buterin unveils plan to curb block builder centralization

Vitalik Buterin is turning his attention to a part of Ethereum most users never think about but that has quietly become one of its biggest pressure points: who gets to decide what transactions goes into a block.

In a new blog post on Monday, the Ethereum co-founder lays out a series of ideas aimed at preventing block building, the process of assembling transactions before they’re finalized onchain, from becoming too centralized.

While Ethereum’s upcoming “Glamsterdam” upgrade will formalize proposer-builder separation, which will allow validators to outsource block construction to a competitive market, Buterin argues that simply creating a marketplace of builders doesn’t solve everything. If a small number of builders dominate, they could still censor transactions or extract outsized profits from users.

One proposal, known as FOCIL, would act as a kind of anti-censorship backstop. Under the design, a small group of randomly selected participants would each choose transactions that must be included in the next block. If those transactions are missing, the block would be rejected. The idea is that even if a single hostile builder controlled the entire market, they couldn’t permanently exclude specific users.

Another focus of his post is so-called “toxic MEV,” where traders exploit visibility into pending transactions to front-run or “sandwich” users’ trades. One potential fix is encrypting transactions until they are finalized, preventing opportunistic actors from seeing them in advance.

Buterin also points to risks at the networking layer, where transactions can be observed by intermediaries before they even reach a block, suggesting that anonymized routing systems could become an important line of defense.

Longer term, he sketches out a vision of more distributed block building, where not every transaction requires full global coordination. Much of Ethereum’s activity, he argues, may not need to be processed in a single, tightly ordered bundle, opening the door to designs that reduce central chokepoints.

Overall Buterin seems to focus on as Ethereum scales, decentralization challenges are shifting from validators to the infrastructure that decides what users’ transactions actually make it onchain.

Read more: Vitalik Buterin reveals his bold new plan to fix Ethereum’s scaling problem