Heh, I have the opposite problem with Prompt - none of my OpenSSH packages are new enough to use the new format, so I can't cross-reference with a known-good SHA-1 fingerprint. Turns out you can run

    cut -d' ' -f2 /etc/ssh/ssh_host_ecdsa_key.pub | base64 -d | openssl sha256 -binary | base64

but this requires actually being on the host (and isn't useful for servers where you don't get a shell).