Debate over Ethereum's ePBS (enshrined Proposer-Builder Separation) upgrade has intensified after Vitalik Buterin posted on X that decentralization risks could migrate to the block building pipeline. While ePBS aims to protect stakers from builder dominance, he identified two major threats: block building power concentrating in few hands, enabling censorship or exploitative MEV strategies like sandwich attacks.
FOCIL and Big FOCIL: Anti-Censorship Framework
FOCIL is introduced as a first step toward in-protocol multi-participant batch creation. It lets 16 randomly selected attesters each choose transactions that must be included in a block; if missing, the batch is rejected. This means even if a hostile actor controls builders, they can't fully censor activity, making inclusion partially distributed rather than centralized.
Big FOCIL expands participant coverage so all transactions can be collectively included. It assigns transactions based on sender address prefixes and prior slot behavior to reduce duplication risk. In this model, builders focus mainly on MEV ordering and state transition computation, not inclusion decisions.
Encrypted Mempools and Network Layer Protection
To counter toxic MEV, encrypted mempools hide transaction details until block confirmation, preventing frontrunning and sandwich attacks. This reduces exploitation in DeFi trading and improves user protection against manipulation. Challenges remain: developers must ensure encrypted transactions are valid and efficiently decrypted only after batch creation.
Vitalik also flagged risks at the transaction ingress layer. User data sent via RPC endpoints or public nodes can be exposed. Suggested solutions include Tor-style routing, mixnets, and bandwidth-heavy but latency-optimized systems like Flashnet, improving privacy without centralized servers.
Long-Term Vision: Distributed Block Building
A broader goal is making Ethereum more distributed, akin to BitTorrent-style coordination. The challenge lies in synchronous shared state, where any action can depend on another, naturally pushing aggregation toward centralized builders.
One proposal categorizes activity: most network usage doesn't require global synchronization, so less-global transaction types can be processed in a distributed way and priced lower, while high-value global actions remain under stricter coordination.
Connection to Ethereum Foundation Strawmap
These discussions align with the recently released Strawmap roadmap, which outlines upgrades every six months through 2029 focusing on scalability, faster batches, privacy, and decentralization. The block building pipeline is a critical component. Concerns around ePBS are technical challenges developers aim to solve as the protocol evolves. The roadmap highlights anti-censorship, fairness, and resilience goals, with FOCIL and encrypted mempools directly supporting those themes.