crypto's quantum problem is really a coordination problem. quantum computers are not about to steal your crypto tomorrow. The bigger risk is that blockchains may take longer to upgrade than quantum computers take to become dangerous. today, ownership onchain is proven through digital signatures your private key signs a transaction, and your public key lets the network verify it. A sufficiently powerful quantum computer running Shor's algorithm could reverse that relationship, recover the private key and create signatures that look completely valid. The blockchain would have no way to distinguish the attacker from the actual owner. This affects the cryptography used across Bitcoin, Ethereum, Solana, Sui and most other chains. Hardware wallets and traditional multisigs do not remove the underlying risk because the attacker is targeting the mathematics behind the keys, not where those keys are stored. no quantum computer can perform this attack today. but recent research has significantly reduced the estimated hardware required, while post-quantum migration remains painfully slow. quantum-resistant signatures already exist, but they are much larger than the signatures blockchains currently use adopting them means changing transaction formats, fees, blockspace, wallets, exchanges, bridges, custody systems and, in some cases, consensus itself. after that, millions of users would still need to move their assets. @projecteleven estimates that "Q-Day" could arrive as early as the 2030s.