Bitcoin Faces Greater Quantum Computing Risk Than Ethereum, Citi Warns

As quantum computing advances faster than expected, a fault line is emerging in the crypto world: Bitcoin may be significantly more vulnerable than Ethereum—and the difference has less to do with code than with politics.

In a research note published this week, Citi analysts warned that recent breakthroughs have shortened the timeline for practical quantum attacks on digital assets. Their conclusion is that not all blockchains will be equally prepared when that threat arrives.

Bitcoin’s exposure is structural. Transactions expose the sender’s public key to the network until confirmed, leaving a window during which a quantum attacker could theoretically derive a user’s private key and redirect funds.

Google’s recent research suggests a 500,000-qubit machine could break that encryption in minutes. Such a machine doesn’t yet exist, but the analysts noted the estimates are continuously improving. Google’s Q-Day estimate—for when a quantum computer powerful enough to break current cryptography comes online—is 2032, but other researchers think it could happen as early as 2030.

The deeper problem is Bitcoin’s governance. Transitioning to quantum-resistant cryptography would require broad consensus across the network, extensive testing, and likely a hard fork—a notoriously difficult process. Its conservative, consensus-driven model, central to Bitcoin’s credibility, also makes rapid protocol changes slow and contested.

Ethereum and other proof-of-stake networks are better positioned, the analysts argued, thanks to more flexible governance and a history of regular protocol upgrades. That said, they are not immune: A quantum-enabled attacker could theoretically acquire enough private keys to control around 33% of a network’s staked assets, enabling disruption of block finality or network operations.

The stakes are sharpened by the scale of Bitcoin’s dormant coin problem. An estimated 6.7 to 7 million BTC sit in wallets where public keys are already exposed—a concentrated target. Among them, roughly 1 million Bitcoin believed to have been mined by the network’s creator, the pseudonymous Satoshi Nakamoto, remain untouched in particularly vulnerable early address formats, worth an estimated $82 billion at current prices.

The analysts pointed to adaptability—not current design—as the defining factor of long-term resilience, flagging BIP-360 and BIP-361 as proposed upgrades to watch for Bitcoin’s quantum readiness.

Citi’s report echoes comments made last week by Fireblocks CEO Michael Shaulov at the Financial Times Digital Asset Summit, where he said Bitcoin’s quantum challenge is “mostly a coordination issue” for the Bitcoin community—not a technical one.