Citi warned on Monday that Bitcoin faces a huge quantum computing threat, with up to 6.9 million BTC already vulnerable.
Summary
- Citi’s May 18 digital asset research note says advances in quantum computing are compressing the timeline for when machines could break Bitcoin’s encryption.
- Bitcoin is particularly exposed because its decentralized governance makes protocol updates slow and difficult to coordinate, unlike proof-of-stake networks.
- An estimated 6.5 to 6.9 million BTC already have public keys exposed on-chain, representing about a third of the circulating supply valued at around $450 billion.
Citi analyst Alex Saunders warned in a May 18 digital asset research note that accelerated advances in quantum computing are shortening the risk timeline for Bitcoin and broader internet infrastructure.
The bank said Bitcoin is particularly exposed because its conservative governance structure makes protocol upgrades slow and difficult to coordinate.
The Citi Institute has been tracking quantum risk to financial systems through 2026, estimating that a quantum attack on a major US bank could put between $2 and $3.3 trillion of GDP at risk, as reported by The Quantum Insider in February.
“While large-scale quantum attacks remain a medium-term concern, the pace of progress has shortened the horizon and deserves greater attention from investors,” Saunders wrote in the note.
Bitcoin governance is its quantum weakness
Citi identified vulnerabilities linked to public keys already exposed on the chain. Older Bitcoin addresses that used payment public key exits left public keys permanently visible, including wallets believed to belong to pseudonymous Bitcoin creator Satoshi Nakamoto. The bank estimates that between 6.5 and 6.9 million BTC contain already exposed keys, worth approximately $450 billion at current prices.
The report noted a risk of “harvest now, decrypt later,” where attackers collect data encrypted today for future decryption using quantum technology. Proof-of-stake networks like Ethereum may be better positioned to respond because they update protocols more frequently, Citi said.
However, the bank warned that they present a larger attack surface. The crypto.news Bitcoin price page shows that Bitcoin is currently trading at around $76,900.
How far away is the real threat?
The bank said it remains constructive on the long-term ability of cryptocurrencies to adapt through post-quantum cryptography. Proposed Bitcoin upgrades, including BIP-360 and BIP-361, are in development, but require broad consensus among miners and node operators, a process that historically takes years.
The broader context of the Bitcoin ecosystem matters here: as crypto.news reported In its Q1 2026 mining sector coverage, the Bitcoin network simultaneously navigates rising energy costs, the AI shift among miners, and the now-increasing institutional scrutiny of its long-term crypto resiliency.
JPMorgan has separate noted that miners moving to AI face high capital needs and potential shareholder dilution, underscoring that the broader Bitcoin infrastructure is experiencing structural stress from multiple directions at once.
