Debian currently ships two versions of GnuPG in every maintained suite -- in particular, /usr/bin/gpg has historically always been provided by the "classic" branch.

That's going to change!

Debian unstable will soon be moving to the "modern" branch for providing /usr/bin/gpg. This will give several advantages for Debian and its users in the future, but it will require a transition. Hopefully we can make it a smooth one.