Buterin Proposes FOCIL for Ethereum Protection

Ethereum co-founder Vitalik Buterin published a detailed roadmap for countering block building centralization in the network. The key element is the FOCIL proposal — a mandatory transaction inclusion mechanism that guarantees protocol-level censorship resistance. The plan is integrated into the upcoming Glamsterdam upgrade.

Block Building Centralization Problem

Currently, over 90% of Ethereum blocks are built by a handful of specialized companies through the MEV-Boost system. This creates censorship risk: large block builders can refuse to include certain transactions under regulatory pressure or for their own commercial benefit.

Buterin noted that the current state of affairs contradicts Ethereum's fundamental principles as an open and neutral platform. Even legitimate transactions are sometimes delayed or excluded from blocks due to decisions by centralized intermediaries.

What is FOCIL

FOCIL (Forward Obligatory Commitment to Inclusion Lists) is a protocol-level mechanism that mandates the inclusion of all valid transactions in a block. Initially, 16 randomly selected attesters will form mandatory inclusion lists for each block.

The block builder is obligated to include all transactions from these lists, regardless of legal pressure or sanctions. This ensures that no valid transaction can be censored at the protocol level.

Enshrined PBS (ePBS)

Alongside FOCIL, the Glamsterdam upgrade will implement ePBS — protocol-level separation of proposer and builder roles. Currently, this separation exists only through external MEV-Boost software, which creates additional risks.

ePBS embeds the separation directly into the Ethereum protocol, making the block building market open and competitive. Proposers (validators) will be able to select blocks from an open builder auction.

Encrypted Mempools

Buterin also proposed encrypting the mempool — the storage for transactions awaiting inclusion in a block. This aims to solve the problem of so-called "toxic MEV": sandwich attacks and frontrunning that cost regular users dearly every year.

If block builders cannot see transaction contents before inclusion, they cannot manipulate ordering for their own benefit. According to developer estimates, this could save Ethereum users hundreds of millions of dollars annually.

Implementation Outlook

The Glamsterdam upgrade is scheduled for the first half of 2026 and will be one of Ethereum's most ambitious updates since the transition to Proof-of-Stake. Buterin emphasized that FOCIL could eventually expand to handle all transactions in a block, reducing the block builder role exclusively to MEV-relevant operations.

The Ethereum community has largely responded positively to the proposals, although some developers have expressed concern about potential protocol complexity increases and higher requirements for validators.