The section of the RFC linked in the comment you're replying to even explicltly states: > All aspects of the "ssh-rsa" format are kept, including the encoded s

The section of the RFC linked in the comment you're replying to even explicltly states: > All aspects of the "ssh-rsa" format are kept, including the encoded string "ssh-rsa". This allows existing RSA keys to be used with the new public key algorithms, without requiring re-encoding or affecting already trusted key fingerprints.