Arthur Hayes, co-founder and former CEO of crypto derivatives exchange BitMEX, has warned that roughly 6.9 million Bitcoin (BTC) sit exposed to future quantum computing attacks, according to COINOTAG. The warning, published October 19, 2026, concerns coins held in addresses whose public keys are already visible on-chain — a condition closely associated with address reuse.

The technical backdrop is well established in Bitcoin security discussions. Spending from an address reveals its underlying public key on the blockchain, where it remains visible permanently. Addresses used only once keep their public keys hidden behind hash-based address formats, but reused addresses leave those keys exposed, meaning a sufficiently powerful quantum computer running Shor's algorithm could in theory derive the corresponding private key and move the funds. Coins from Bitcoin's earliest era, held in pay-to-public-key outputs, face the same structural exposure. Because exposed keys are visible to anyone reading the blockchain, the risk surface is determined by observable on-chain data rather than by any current attack — one reason single-use address hygiene has long been treated as a core part of Bitcoin operational security.

The hardware timeline behind the debate moved on Monday. In a 22:03 UTC update, COINOTAG reported that quantum computing firm Quantinuum announced an error-correction record on its Helios machine: a logic error rate of 5 per million operations, equivalent to 99.9995% logical fidelity — cutting errors tenfold from its September result. Error correction, which combines many noisy physical qubits into more reliable logical qubits, is widely regarded as a prerequisite for quantum machines capable of attacking elliptic-curve cryptography at scale, which is why fidelity milestones like this one are among the benchmarks researchers use to gauge progress toward that threshold.

Hayes's warning and Quantinuum's announcement sit within a broader technical debate over how long Bitcoin holders have before quantum hardware advances from laboratory milestones to cryptographically relevant capability. No date for such a transition has been established, and estimates of the exact size of the exposed coin supply vary. Within Bitcoin's developer community, proposals to introduce quantum-resistant signature formats have circulated as a potential long-term migration path, though no such change has been adopted into the protocol. For observers tracking the issue, the incremental markers are further vendor error-correction results, growth in logical qubit capability, and any movement on quantum-resistant proposals through Bitcoin's improvement process.

This content was first published on COINOTAG: https://en.coinotag.com/arthur-hayes-bitcoin-address-reuse-quantum-risk