I don't think it's quite right to say they never leave your device. The page you linked says: "To address the common case of device loss or upgrade, a key fea

I don't think it's quite right to say they never leave your device. The page you linked says: "To address the common case of device loss or upgrade, a key feature enabled by passkeys is that the same private key can exist on multiple devices. This happens through platform-provided synchronization and backup."