We do have another IP tied to the anycast cloud on a different /8.

149.112.112.112 - blocking, no edns (same setup/config as 9.9.9.9)

I will see about adding this to the list of things to add to documentation. (thanks for the feedback guys!)

Following Google's pattern, the secondary server should be 9.9.(4.5).(4.5)

if it's anycast, it shouldn't matter. if the first IP is down, chances are the second one would be down as well, unless they announce the IPs seperately or something.