Quantum Advisory Report Puts Bitcoin’s Abandoned-Coin Problem at the Center of Post-Quantum Planning
Coinbase’s independent Quantum Advisory Council published a report examining what Bitcoin and other blockchain communities should do with coins that are never migrated before a future quantum threat. The report highlighted Bitcoin’s exposed legacy outputs and reframed post-quantum migration as a governance problem as well as a cryptographic one.
On June 11, 2026, Coinbase’s independent Quantum Advisory Council published a report on one of the hardest unresolved questions in post-quantum cryptocurrency planning: what should happen to coins that remain in quantum-vulnerable addresses after a migration path becomes available. The council did not claim that quantum computers could break Bitcoin in 2026 and did not advocate a single policy. Instead, it examined the tradeoffs between preserving existing ownership rights, freezing vulnerable coins, or taking more aggressive measures against assets that never migrate.
Bitcoin occupied a particularly important place in the analysis because of the age and structure of its UTXO set. Coinbase summarized the report as estimating roughly 1.7 million BTC in old pay-to-public-key outputs where public keys are already exposed, with a much larger total potentially vulnerable when address reuse and other exposed-key conditions are included. Some of the oldest coins are believed to include early-mined or lost holdings, making the issue inseparable from questions about abandoned property, presumed ownership, and whether the network should ever invalidate spendability for security reasons.
The technical problem and the governance problem are different. Adding new signature schemes or quantum-resistant spending paths can be approached as engineering work. Deciding what to do with coins whose owners never migrate is a social and policy choice with consequences for Bitcoin’s monetary rules, property expectations, and supply. A future attacker capable of deriving private keys from exposed public keys could otherwise claim coins whose legitimate owners were inactive, dead, unaware, or unable to move them.
The June report belongs in Bitcoin history because it helped move the quantum discussion beyond abstract cryptography and into concrete questions about Bitcoin’s oldest UTXOs and the limits of protocol intervention. Other June studies produced different exposure estimates, and those estimates should be treated as supporting research rather than separate timeline events. The historical development was the emergence of the abandoned-coin governance problem as a formal subject of post-quantum migration planning.