Bitcoin's Quantum Risk Is Real but Not Imminent, Coinbase Says

Coinbase estimates that exposed public keys make part of Bitcoin's supply vulnerable to a future quantum attack. Today's machines are far too small, leaving the network time to migrate if developers act early.
Quantum computers do not pose an immediate threat to Bitcoin, but the network has a migration problem that becomes harder if users reuse addresses.
Coinbase Research estimates that roughly 6.51 million bitcoin, about 32.7% of supply at block 900,000, sit in output types whose public keys are already exposed. A sufficiently powerful quantum computer could, in theory, derive private keys from those public keys and authorize unauthorized spending.
That machine does not exist today. Coinbase noted that the most advanced systems have fewer than 1,000 qubits, far short of the scale required to break Bitcoin's cryptography. The near-term probability is therefore low, and no observed loss in the cited evidence was caused by a quantum attack.
Address reuse still matters because spending from an address reveals its public key. Older pay-to-public-key outputs, bare multisig and Taproot outputs can also expose keys in ways that create a long-range target. Every output may face a short window of vulnerability when its public key appears in the mempool during a spend.
Developers are considering paths such as BIP-360 and other quantum-resistant signature schemes. A migration would require years of standards work, wallet updates, node adoption and decisions about old coins. Larger post-quantum signatures could also raise storage, verification and fee costs.
For holders, the practical lesson is operational rather than predictive: avoid unnecessary address reuse and keep wallet software current. For the network, the challenge is to agree on a migration before quantum capability becomes urgent. Bitcoin's risk is not a present breach, but a slow coordination problem with a potentially severe endpoint.
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