What happened
Alex Pruden, the chief executive of Project Eleven, told CoinDesk in an interview published Wednesday that Bitcoin's transition to a post-quantum signature scheme will be a heavier engineering lift than Taproot, and that Core developers should stop treating it as a research problem. Pruden's framing was direct: the asymmetry between acting on a post-quantum signature scheme today and waiting for certainty about quantum-computing hardware means the bias should be toward shipping.
Project Eleven runs research on quantum-resistant cryptography for blockchains, so Pruden has a horse in this race, and he didn't pretend otherwise. The comments land in a debate that has been simmering inside the Core developer community for years without a clear path to a Bitcoin Improvement Proposal that could actually activate.
Why it matters
Bitcoin's signature security rests on the elliptic-curve discrete logarithm problem, which a sufficiently large fault-tolerant quantum computer running Shor's algorithm could break. Estimates of how many qubits that takes vary wildly, and that's the point Pruden is exploiting. If you wait until the threat is provable, you've already lost the coins in any address whose public key has been exposed on-chain, including early Satoshi-era pay-to-public-key outputs and any address that has ever spent.
On-chain analyses have long pegged the at-risk float at around 4 million BTC, a figure that includes the dormant 2009-2010 mining rewards. A migration also can't be rushed at the moment of crisis. Taproot, a far smaller change to the signature model, took roughly four years from BIP draft in 2018 to mainnet activation in November 2021, and it didn't replace ECDSA.
