Bitcoin quantum “harvest now, decrypt later” risk rises

Security researchers warn that Bitcoin quantum risk is increasing via a “harvest now, decrypt later” strategy: adversaries can collect encrypted blockchain data today and decrypt it after quantum capability improves. A March 2026 Google Quantum AI paper estimates cracking Bitcoin’s secp256k1 signatures could take as few as ~1,200 logical qubits—around 20x fewer resources than earlier estimates. No current quantum computer reaches that level, but Project Eleven expects cryptographically relevant “Q-Day” quantum systems between 2030 and 2033. The exposure is already measurable. Citi and Project Eleven (May 2026) estimate 6.5–6.9 million BTC have public keys exposed on-chain, worth roughly $450–$500 billion at current prices. Public key exposure typically occurs when an address has spent before (spending reveals the key), while never-spent addresses mainly expose only hashed values. Some holdings may be dormant, potentially including addresses linked to Satoshi Nakamoto. The article also highlights governance and upgrade friction. A fast, sweeping Bitcoin standard change would require coordinated updates across nodes, miners and wallet providers, plus user migrations to new address formats. Citi argues this is slower and more contentious than post-quantum upgrade paths on proof-of-stake networks like Ethereum. For traders, this is mainly a long-horizon tail risk for Bitcoin, but it can still move sentiment and drive rotation toward networks seen as faster in post-quantum readiness.