Login Agent now supports manually pre-loading the public keys on PIV smart cards (ex. YubiKey 4/Neo). This can be handy when you want to test your PIV smart card without creating an Address Book entry. It can also be used to cache the PIN for your PIV smart card even when you disabled the "Cache SSH login data" option in Login Agent.
Do you want to add your YubiKey to your SSH server account? No problem! Just plug in your YubiKey and get its public key in OpenSSH format by using the "Copy Public Key to Clipboard" menu in Private Keys panel. You can then paste the public key to your server settings just like any other key, no muss, no fuss.