Citi warns Bitcoin faces outsized quantum threat

Citi warned Monday that Bitcoin faces an outsized quantum computing threat, with up to 6.9 million BTC already vulnerable.

Citi analyst Alex Saunders warned in a May 18 digital asset research note that accelerating quantum computing advances are shortening the timeline for risks to 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 throughout 2026, estimating that a quantum-enabled attack on a major US bank could put $2 to $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 warrants closer attention from investors,” Saunders wrote in the note.

Bitcoin’s governance is its quantum weakness

Citi identified vulnerabilities tied to public keys already exposed on-chain. Older Bitcoin addresses using pay-to-public-key outputs left public keys permanently visible, including wallets believed to belong to Bitcoin’s pseudonymous creator Satoshi Nakamoto. The bank estimates 6.5 to 6.9 million BTC hold already-exposed keys, worth roughly $450 billion at current prices.

The report flagged a “harvest now, decrypt later” risk, where attackers collect encrypted data today for future quantum-enabled decryption. Proof-of-stake networks such as Ethereum may be better positioned to respond because they upgrade protocols more frequently, Citi said.

However, the bank warned they present a larger attack surface. The crypto.news Bitcoin price page shows Bitcoin currently trading at around $76,900.

How far away is the actual threat?

The bank said it remains constructive on crypto’s long-term ability 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.

Broader Bitcoin ecosystem context matters here: as crypto.news reported in its Q1 2026 mining sector coverage, the Bitcoin network is navigating simultaneously rising energy costs, the AI pivot among miners, and now growing institutional scrutiny of its long-term cryptographic resilience.

JPMorgan has separately noted that miners pivoting to AI face high capital needs and potential shareholder dilution, underlining that the broader Bitcoin infrastructure is undergoing structural stress from multiple directions at once.