Google's Willow Error Cut and an AI-Designed Circuit Shrink Two Costs of Attacking Bitcoin's Keys

Two research results published within a day of each other reduce different parts of the cost of a future quantum attack on bitcoin's signatures. Neither one breaks bitcoin today. Taken together, they show that the hardware cost and the algorithm cost are falling at the same time.

The first result came from Google Quantum AI. In a paper published in Science on October 15, researchers reported using a technique called magic state cultivation on the Willow superconducting processor to prepare the specialized quantum states that error-corrected machines need for advanced calculations. CoinDesk reports that the states had about 40 times fewer errors than states prepared without the method. Google called the resulting 99.99% fidelity a record. The process remains costly. According to crypto.news, only about 8% of attempts passed every check, so the chip discards more than nine of every ten tries to keep one clean state.

The second result came from Anthropic. The company said its Claude Mythos model designed quantum circuits that could bring quantum computing "within reach sooner." Interesting Engineering reports that, working from plain-language instructions, the model outperformed the best published designs on seven of eight tasks. One design used 17 times fewer gates in exchange for 12% more qubits. Among the outputs was a reversible arithmetic routine for elliptic-curve calculations. Shor's algorithm needs exactly that kind of arithmetic to derive a private key from a bitcoin public key. Researchers from Harvard University and QuEra Computing took part in the work.

The industry response arrived on October 16. Nine companies, including the auditor Hacken, Cardano founder Charles Hoskinson's Midnight Foundation, Quantus and Postquant Labs, formed the Quantum Alliance to draft security standards. The group estimates that about 6.4 million bitcoin, or 30.2% of supply, sit in outputs whose public keys are already visible on-chain. PANews reports that this figure includes roughly 1.1 million coins attributed to Satoshi Nakamoto. Glassnode's earlier estimate, cited by crypto.news, is lower at 6.04 million.

The members agree on the exposure and disagree on the remedy. TFTC reports that Postquant Labs' chief technology officer favors migrating coins to quantum-resistant outputs. Bryn Bennett of The Vault opposes freezing coins, arguing that a freeze would break bitcoin's promise against confiscation. The incentives are worth noting. Several alliance members sell post-quantum products, and an urgent timeline would help their business. That conflict of interest does not make the published hardware and circuit results false. It does mean their claims about timing deserve more scrutiny than the papers themselves. CoinDesk recorded bitcoin as little changed near $82,100 on October 16, so the market has not priced either result as an immediate threat.