What Is Q-Day? The Quantum Threat to Bitcoin Explained

Quantum computers can’t break Bitcoin’s cryptography today, but new advances in the field suggest the gap is closing faster than expected. Progress toward fault-tolerant quantum systems raises the stakes for “Q-Day,” the moment when a sufficiently powerful machine could crack older Bitcoin addresses and expose more than $711 billion in vulnerable wallets. Long seen as a distant threat on the horizon, Q-Day snapped into sharp focus in March 2026, with multiple research papers suggesting that quan...