Vitalik Buterin says Ethereum is about to go through its biggest rebuild since the Merge, and even his own researchers are telling him to move faster.
Ethereum has torn up its own blueprint twice before, once when it launched as a proof-of-work chain in 2015 and again when it switched to proof of stake at the Merge in 2022. On July 4, Buterin told the network to get ready for a third overhaul, one he says will touch nearly every layer of the protocol over the next three to four years.
He's calling it Lean Ethereum, and according to Coindesk, Buterin described it as the network's biggest rebuild since the Merge. That's not a small claim from the person who co-founded the chain. The plan isn't a single hard fork with a catchy name. It's a rolling series of upgrades to consensus, cryptography, data availability and execution, stretched across years rather than delivered in one release.
Three priorities sit at the center of it. Quantum resistance has moved up the list, with Buterin arguing that hash-based signatures need to replace the BLS signatures Ethereum validators currently rely on before quantum computers become a genuine threat to the chain's security. Privacy is being built into the base layer instead of bolted on afterward. Privacy, he said, is no longer an afterthought, it's a first-class goal. And scalability keeps climbing through a string of smaller upgrades rather than one dramatic leap, with gas limits rising, blob capacity expanding, and slot times shrinking as client teams prove higher throughput is safe.
Under the hood, the plan splits into pieces that mirror the lean branding. Lean Consensus redesigns the Beacon Chain to reach finality in seconds and swaps in quantum-resistant signature schemes. Lean Data stretches the blob-based model Ethereum adopted with EIP-4844, adding variable blob sizing and post-quantum data availability sampling. Lean Execution proposes a minimal, SNARK-native instruction set, possibly built on RISC-V, that stays compatible with the EVM while being far cheaper to verify with zero-knowledge proofs. A team called Ream Labs runs the public tracker at leanroadmap.org, and the code already lives in the open on GitHub under projects like leanVM, leanSig and leanMultisig.
None of this replaces the rollup-centric roadmap Ethereum has followed since 2021, the one built around phases like the Surge, the Verge and the Purge. Lean Ethereum sits on top of it as the next act, the one that assumes rollups have already scaled the chain and now asks what the base layer needs to survive the next decade.
The reaction from Ethereum's own research community has been warm on substance and blunt on pace. Dankrad Feist, a researcher at the Ethereum Foundation, praised the vision but told Buterin that three to four years is too slow, arguing the work could realistically get done in about a year with help from large language models speeding up development. Eli Ben-Sasson, the StarkWare co-founder who helped pioneer the STARK proofs Lean Ethereum leans on, was blunter about it. Many good things, a few unclear things, still a few problems, he said, adding that waiting three to four years is simply too long given how urgent quantum readiness has become.
Buterin did leave a near-term marker. He said the Glamsterdam upgrade will bring a large jump in network capacity, and that the fork after it, carrying the internal codename Hegotá, is probably Ethereum's last upgrade that still belongs to the old, pre-Lean era. The fork after that one, he said, will carry what he called a very strong Lean feel.
That's a real deadline dressed up as a soft one.
Ethereum has spent years telling the market that rollups would handle scaling while the base chain stayed simple. Lean Ethereum is Buterin admitting that simple isn't good enough anymore, not with Solana processing thousands of transactions a second on a single execution layer and quantum computing research advancing fast enough that cryptographers want new signature schemes in place well before anyone builds a machine that can break the old ones.
For validators and stakers, the practical stakes are signature schemes and client software, not price charts. Hash-based signatures like those in the leanSig library take more space than the BLS signatures Ethereum uses now, so node operators will eventually need to budget for larger proofs and heavier verification, even as the SNARK-native execution layer tries to claw that cost back. For the L2s built on top of Ethereum, from Arbitrum to Base, the near-term reality doesn't change much. Their rollups still settle on the existing chain, and the Lean upgrades are designed to stay compatible with the EVM rather than strand anyone who built on it.
Buterin has set the direction. Whether Ethereum can move at the pace its own researchers are now demanding is the argument that actually decides what the next four years look like.
Also read: BonkDAO Says a Malicious Governance Vote Just Drained $20 Million in BONK • Ripple Wins Full EU Crypto License While Hundreds of Rivals Get Shut Out • Trump Rings NYSE Bell From the Oval Office and Says Nobody Understands Bitcoin's Power
