A quantum computer could theoretically derive private keys from exposed public keys and drain Bitcoin wallets—hypothetical Q-Day—though no such machine exists today and timelines vary widely. Three approaches are being developed: quantum-resistant transactions under current rules, protocol upgrades like a soft fork, and custody-layer defenses. StarkWare cut the estimated cost of a quantum-resistant Bitcoin transaction from $320 to roughly $67 in a single week through an open competition. Coinbase, which safeguards roughly $250 billion in assets, is building post-quantum custody designed to adapt to any signature scheme Bitcoin eventually adopts. Nothing concrete this week makes Bitcoin quantum-resistant on its own, but the field is shifting from theory to logistics.
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