In a new blog post, Google Research warns that quantum computers could break the security architecture of various cryptocurrencies sooner than anticipated. According to the company’s researchers, an attack on Bitcoin may be possible with fewer than 500,000 physical qubits — roughly 20 times fewer than earlier estimates suggested.
For Bitcoin, a particularly critical scenario is what the authors describe as an “on-spend attack.” In this case, a quantum computer would derive the private key from a publicly exposed key while a transaction is still in the mempool. Under Google’s assumptions, this process could take around 9–12 minutes, potentially within Bitcoin’s average block time of approximately 10 minutes.
Not Only Bitcoin at Risk
The authors emphasize that this does not imply an immediate collapse of the crypto market. Instead, they recommend a structured transition to post-quantum cryptography. Google is also participating in the quantum race with its Willow processor and plans to complete its own migration to quantum-resistant algorithms by 2029.
The risk extends beyond Bitcoin wallets to Ethereum accounts, smart contracts, Proof-of-Stake validators, and dormant wallets with long-exposed public keys. The document estimates that up to 2.3 million BTC could currently reside in potentially vulnerable wallets. Another study suggests that as many as one in three bitcoins could be at risk.
At the same time, Google notes that not every worst-case scenario is realistic. For example, Bitcoin mining itself is not considered the primary attack vector. The key takeaway from the research is that the crypto industry should no longer delay the transition to quantum-resistant security methods.
Google’s findings indicate that the quantum threat is gradually shifting from theoretical risk to practical consideration. While there is no immediate danger, the crypto industry must accelerate adoption of post-quantum cryptography. Projects that begin adapting early may strengthen investor confidence and institutional trust.
