Hello Joseph
By default the classless feature is enabled. Before IOS version 11.3, the default was disabled. You can find out more info at this CLI command reference:
In order to see what mode you are in, you can take a look at the running configuration. If you see the
no ip classless command exists, then you are running in classful mode. If the ip classless command exists or if there is no such command at all, then you are running in classless mode.
I hope this has been helpful!
Laz