A Citi research note from May 18, 2026 concludes that Bitcoin faces significantly greater quantum risk than Ethereum, citing governance and technical architecture. The warning follows a March 2026 paper by Google Quantum AI, Stanford, and the Ethereum Foundation, which found that breaking Bitcoin's elliptic curve cryptography requires about 20 times fewer resources than previously estimated—potentially allowing a quantum computer with under 500,000 qubits to derive a private key in nine minutes. Bitcoin's conservative governance makes upgrades slow; SegWit took 8.5 years, and current quantum proposals (BIP-360/361) remain in draft. In contrast, Ethereum's Pectra upgrade (May 2025) introduced EIP-7702 for account abstraction, enabling voluntary adoption of quantum-safe signatures. The Hegotá hard fork (H2 2026) further embeds post-quantum infrastructure. Author Sam Tabar, who built a large corporate Ethereum treasury, argues Ethereum's structured roadmap makes it more resilient. Institutional treasurers face growing regulatory pressure, with U.S. federal agencies already required to submit post-quantum transition plans by April 2026.

Key facts

• Citi warns Bitcoin's quantum risk is higher than Ethereum's due to governance and architecture.
• Google/Stanford paper: quantum computer could break Bitcoin keys in 9 minutes.
• Bitcoin's upgrade pace is slow; SegWit took 8.5 years.
• Ethereum's Pectra upgrade enables voluntary quantum-safe signatures via EIP-7702.
• US federal agencies required to submit post-quantum plans by April 2026.

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