Ethereum's quantum plan gets a one-way switch: draft EIP would retire BLS for good

The mechanical problem is a schema mismatch. Ethereum's deposit contract has fixed-size fields, post-quantum validator keys do not fit inside them, so the draft makes the fields variable length and puts the irreversible BLS off switch in the same document ^[6][2].

The sizes are where the cost lives. BLS signatures run 96 bytes; leanXMSS, the hash-based scheme the Ethereum Foundation has picked as the replacement, runs close to 3,000 ^[12]. That is about a 31-fold increase per signature ^[21], landing on a consensus layer whose current efficiency comes from folding hundreds of thousands of validator signatures into one, according to ethereum.org's quantum-resistance page ^[10]. Cryptopolitan's account of the draft does not say whether the hash-based scheme preserves that aggregation. Until someone publishes that, the 31x figure is a floor on per-signature growth and tells you nothing final about per-slot bandwidth.

Nothing here is near shipping. Wedderburn says the draft is unfinished and that large portions are boilerplate covering EIP-7685 mechanics ^[4], and it still has to be blended with validator EIPs 7251, 7002 and 8282 ^[5]. It was filed as pull request 12235 in the ethereum/EIPs repository, with Thomas Coratger and Tom Wambsgans listed as co-authors ^[3][7]. Merging four validator EIPs into one coherent deposit path is the gate on the schedule, not editor review.

And this is one quarter of the job. Vitalik Buterin's February 2026 roadmap set out four workstreams: validator BLS signatures, KZG commitments behind data availability, the ECDSA signatures guarding ordinary accounts, and the zero-knowledge proof systems rollups depend on ^[16]. Core layer-1 quantum upgrades are targeted for roughly 2029, which both ethereum.org and Cryptopolitan describe as a planning goal that could move ^[15]. NIST plans to deprecate ECDSA by 2030 and disallow it by 2035 ^[14], so the current target leaves one year of clearance on the first date and six on the second ^[22].

The Foundation is not treating this as speculative work. It named a dedicated post-quantum team in January 2026, with Coratger among its leaders ^[18], and attached a $1 million Poseidon Prize for hardening a hash function on top of an earlier $1 million Proximity Prize ^[19], or $2 million in bounties for cryptographic groundwork ^[23]. Justin Drake called the effort a "top strategic priority" ^[20].

The threat itself has not arrived. Machines capable of running Shor's algorithm against elliptic curve cryptography do not exist anywhere ^[11], but a March 2026 Google Quantum AI document cut the estimated cost of breaking the 256-bit curve Ethereum uses by around 20 times, per ethereum.org ^[13]. That is what turns a research topic into a deposit contract rewrite with a switch that only turns one way.