Organizations should begin migrating to post-quantum cryptography immediately, the G7 Cybersecurity Working Group said in its September 3, 2026 report, "Preparing for the Post-Quantum Era: A Call to Action." The report describes quantum computing as a security and economic threat to public and private organizations, warning that recent advances could eventually threaten widely used public-key cryptography even though the timeline remains uncertain. The advisory does not mention cryptocurrency by name, but its implications extend directly to blockchain networks, exchanges and custodians because public-key cryptography secures wallets and authorizes transactions. Attackers could use a "harvest now, decrypt later" strategy, while permanently visible blockchain data and exposed public keys could leave older wallets vulnerable to retrospective attacks. The European Union adopted a coordinated post-quantum transition roadmap in June 2025, requiring member states to begin transitioning by the end of 2026 and high-risk entities to complete migration before 2030. Bitcoin developers are exploring BIP-360, which has no activation date, while Ethereum is targeting core post-quantum infrastructure for 2029. Solana has tested post-quantum signatures and introduced an optional hash-based vault. Migration presents significant technical and governance challenges. A secp256k1 ECDSA signature is about 64 bytes, compared with approximately 4,595 bytes for Dilithium-5 and 4,627 bytes for ML-DSA-87. The larger signatures could increase storage, bandwidth and transaction costs. Research from Google Quantum AI and draft NIST guidance calling for the phaseout of vulnerable ECDSA systems add urgency to planning, while the G7 says coordinated action across the public and private sectors is necessary.