Vitalik Buterin says Ethereum is preparing its ‘biggest rebuild’ since the Merge

Ethereum co-founder Vitalik Buterin has a fresh set of takeaways on “Lean Ethereum,” the multi-year plan to rebuild nearly every major part of the network, following research meetings.

He termed it the third major iteration of Ethereum after the 2022 Merge that switched the network from mining to a stake-based system, with almost every major piece of the protocol set to be replaced over three to four years while keeping disruption to existing applications low.

The ambitious Lean Ethereum idea was first laid out in July 2025 as a technical framework for the network’s next decade, built around superior cryptography compared with most methods currently in use.

Buterin’s update – accompanied by a revised roadmap internally called a strawmap – gave further details on where the effort is heading and what has moved up in priority.

Quantum safety has moved sharply up the list of priorities. Reigning theories state a powerful enough quantum computer could eventually break the cryptography that secures blockchains, a risk the industry increasingly treats as worth preparing for even if it remains years away.

But Ethereum now treats replacing every quantum-vulnerable part with a quantum-safe alternative as urgent, Buterin said, including a redesign of the cheap data storage that rollups, the layer-2 networks built on top of Ethereum, depend on.

Privacy has been raised to what Buterin called a ‘first-class goal’ rather than an afterthought. The plan calls for designing core network components so that private, intermediary-free transactions can pass through them by default.

The way the network checks itself is also changing. Instead of every node re-running every transaction, Ethereum plans to rely on recursive STARKs. This cryptographic proof method allows a node to verify a compact proof that the work was done correctly, rather than repeating it. That shift is meant to make the network faster and lighter to run.

As such, the change Buterin flagged as most disruptive is to what Ethereum calls state. State is a blockchain’s current memory, the complete snapshot of everything that exists on a network at a specific point in time.

Think of it as the running record of every account balance and all the data those contracts hold (such as who owns which NFT, how much is in a lending pool, every token ledger), as of the latest block.