Circle's L1 blockchain, Arc, has announced a quantum-resistant design and roadmap aimed at achieving full-stack quantum resistance. The plan includes phased implementation covering wallet authorization, private state, validator authentication, and infrastructure. A quantum-resistant signature mechanism will be introduced on the mainnet using an opt-in approach to avoid mandatory migration. The roadmap outlines steps to enhance quantum-resistant private state protection, infrastructure upgrades including TLS 1.3, and validator signature strengthening. Circle warns that quantum computing could threaten public key cryptography by 2030 or sooner, highlighting the risk of 'collect now, decrypt later' scenarios.