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Ethereum co-founder Vitalik Buterin released a detailed post examining how to reduce centralization risks in Ethereum’s block construction process, arguing that the way transactions are organized before they reach finality has become a key vulnerability for the network’s decentralization.
Buterin described block construction as the process of organizing transactions prior to finality on the blockchain. He said this pipeline can be exploited when a small set of advanced operators repeatedly controls block construction, allowing them to strategically order transactions to maximize extractable value. That dynamic, he argued, can create competitive advantages over smaller participants.
Buterin pointed to the planned Glamsterdam upgrade, expected in the first half of 2026, which will deploy enshrined Proposer-Builder Separation (ePBS). The upgrade is designed to divide block proposers from builders by allowing proposers to outsource block construction to a “free permissionless market” of builders.
Buterin said ePBS helps ensure builder centralization does not automatically translate into staking centralization. However, he cautioned that it may not fully prevent builder concentration, which could still enable transaction censorship or disproportionate profit extraction from network users.
To address censorship concerns, Glamsterdam will incorporate Forward Obligatory Commitment to Inclusion Lists (FOCIL). Buterin said FOCIL designates 16 randomly chosen participants who each specify transactions that must be included in subsequent blocks.
Under the mechanism, blocks that do not include the mandated transactions would be rejected. Buterin argued this would prevent even a scenario where a single malicious entity controls block construction from censoring transactions.
He also described an expanded approach called “Big FOCIL,” which would manage all block transactions rather than a subset. In this design, builders would be restricted primarily to MEV-related operations and state computations, effectively commodifying block construction.
Buterin also examined “toxic MEV,” where traders can exploit visibility into unconfirmed transactions to frontrun or sandwich other users. His recommended mitigation is mempool encryption, which would protect the transaction queue awaiting confirmation.
By encrypting transactions until block inclusion, he said it would reduce the ability for actors to exploit transactions before they are confirmed.
Buterin further highlighted that vulnerabilities can exist at the network infrastructure level, where intermediaries may monitor transactions before they reach block builders. He referenced privacy-preserving tools such as Tor and Ethereum-specific mixnets like Flashnet as potential protections.
He also noted the Ethereum Foundation’s Kohaku privacy initiative as relevant ongoing work.
Buterin’s analysis is part of an extended series of technical assessments published over recent days, with earlier installments covering topics such as quantum resistance strategies and execution layer modifications.
Earlier this year, he said he would sell ETH to fund open source development as the Ethereum Foundation entered what he described as a “period of mild austerity.”
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