It depends on the base plate anchor bolt layout in my opinion, but most braced frame models I see are pinned in the major and minor axis at the base. If you are working with flexible diaphragms you might have to keep the frame out-of-plane rotation fixed to prevent instability (frame falling over). Spring foundations are also possible in RAM SS now, in case you want to explore a partially fixed base condition.
I can't think of a good reason to fix the base plate at a braced frame, as drift will almost certainly not be a problem. You'd just be adding cost for no good reason.
