Prime Spock currently has a full beard, which is the opposite of his usual completely clean-shaven appearance.
So this must mean that at this point in the chronology, Mirror Universe Spock has big mutton chops but no mustache or any hair on his chin or below the lower lip. In terms of facial hair, that would be the opposite of the trim goatee that he would later be famous for.
Kor
Having flashbacks to beared David Hasselhoff vs. non-bearded David Hasselhoff. Battle of the ages.