Vitalik Details Ethereum Block Building Overhaul Plan

• ePBS separates proposers and builders, limiting staking power spillover but not full builder concentration.
• FOCIL and “Big FOCIL” aim to enforce transaction inclusion and strengthen censorship resistance.
• Encrypted mempools and anonymized routing target frontrunning, sandwiching, and RPC-level surveillance risks.

On Monday, Vitalik Buterin outlined new plans to reshape Ethereum’s block building process. He focused on reducing block builder centralization ahead of the Glamsterdam upgrade, expected in the first half of 2026. The discussion followed recent posts on execution changes and quantum resistance, explaining why block construction needs structural reform now.

ePBS And The Push to Separate Power

Buterin explained that Glamsterdam will introduce enshrined Proposer-Builder Separation, known as ePBS. This system allows validators to outsource block construction to a permissionless builder market. According to Buterin, this prevents block builder dominance from spilling into staking power.

However, he noted a remaining risk. While ePBS protects staking, block building itself may still concentrate among advanced actors. Those builders often optimize transaction ordering to extract value, which can influence validator behavior. Therefore, Buterin framed ePBS as necessary but incomplete.

FOCIL, Big FOCIL, And Censorship Resistance

To address censorship risks, Buterin highlighted Forward Obligatory Commitment to Inclusion Lists, or FOCIL. Under this system, 16 randomly selected attesters force transaction inclusion. If required transactions are missing, the network rejects the block.

He then described a possible expansion called “Big FOCIL.” In this model, FOCIL participants could include most transactions themselves. Builders would then focus mainly on MEV-related activity and state execution. This structure limits censorship even if builders become highly concentrated.

Encrypted Mempools And Network-Layer Risks

Buterin also addressed risks before transactions reach blocks. He pointed to sandwiching, frontrunning, and transaction griefing as persistent problems. Encrypted mempools could prevent these attacks by hiding transaction details until inclusion.

Beyond mempools, he emphasized the transaction ingress layer. Routing through public RPCs or mempools exposes users to surveillance. He cited growing research into anonymized routing using tools like Tor and Ethereum-focused mixnets such as Flashnet. According to Buterin, this remains an open design space tied to ongoing work by the Ethereum Foundation.