Here's the commit that removes the Public/All timeline (the above image mentions that removal): https://code.gab.com/gab/social/gab-social/-/commit/7ad7fe06...
Couldn't find when exactly Federation capability was removed, since that's less obvious from the commit messages (as someone who doesn't know Mastodon internals).
It's still based on the Mastodon fork, but they seem to have been changing the code constantly even before this (based on information under #gab on Mastodon), so it's not clear how much it resembles the Mastodon source by now.
PS: Somehow looking at the source repo and commit messages makes this more "real" for me, more than any screenshots or the user-facing site itself. It's a weird feeling.
Wikipedia is not completely clear about the subject ("customized Mastodon fork") :
https://en.wikipedia.org/wiki/Gab_(social_network)