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Ethereum’s roadmap for 2026 is no longer just about scaling. Vitalik Buterin is now targeting a quieter risk: the concentration of power inside block building itself.
In a detailed breakdown of Ethereum’s block production pipeline, Buterin questioned whether enshrined proposer-builder separation (ePBS), set for the Glamsterdam upgrade in the first half of 2026, truly protects decentralization or merely shifts influence to specialized builders.
Finally, the block building pipeline.
In Glamsterdam, Ethereum is getting ePBS, which lets proposers outsource to a free permissionless market of block builders.
This ensures that block builder centralization does not creep into staking centralization, but it leaves the…
— vitalik.eth (@VitalikButerin) March 2, 2026
Glamsterdam introduces ePBS directly into Ethereum’s consensus layer, allowing validators to outsource block construction to a permissionless market of builders. In theory, this prevents builder power from merging with staking pools.
Buterin argues that separation alone doesn’t solve builder centralization. Block construction rewards actors with superior infrastructure, private order flow and advanced MEV strategies. Over time, that advantage can compress the market into a handful of dominant builders.
The trend isn’t hypothetical. Since MEV-Boost’s rise in 2022 shifted most Ethereum blocks to outsourced builders, block production has increasingly flowed through a small number of relays and sophisticated operators.
That risk is structural, because if ordering power concentrates, builders gain leverage over transaction sequencing, latency arbitrage and extraction strategies. Decentralization at the validator layer wouldn’t fully offset that imbalance.
Ethereum developers plan to introduce FOCIL, short for Forward Obligatory Commitment to Inclusion Lists. Sixteen randomly selected attesters will nominate transactions that must appear in the next block, and if excluded, the block fails validation.
The mechanism ensures that even a hostile builder controlling block production can’t permanently censor transactions.
Buterin extends this idea with “Big FOCIL.” Inclusion lists could scale to cover all block transactions. Builders then focus primarily on MEV-sensitive ordering and state execution rather than discretionary inclusion.
This would reduce builders to execution engines rather than gatekeepers while shifting power back toward protocol-defined inclusion rules.
Buterin also targets toxic MEV, including sandwich and frontrun attacks that rely on visible pending transactions. Encrypted mempools would hide transaction details until inclusion, removing the window for opportunistic wrapping.
The technical hurdle is precise. The network must verify validity while ensuring decryption happens only after block construction, because any failure risks breaking mempool efficiency.
He further highlights the transaction ingress layer. Transactions sent through public RPC endpoints or the open mempool can be observed in flight. Research into Tor routing, Ethereum-specific mixnets and low-latency systems such as Flashnet seeks to limit that exposure.
The direction is becoming harder to ignore as Ethereum approaches 2026, with decentralization pressure migrating from staking pools to the infrastructure that assembles blocks. Big FOCIL and encrypted pipelines represent an attempt to hard-code limits on builder power before it becomes entrenched.
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