Dear student,

Csab special round counseling for nits, iiits, iiest and gftis is held to fill the vacanct seats after the josaa counseling.
The csab special round counseling is held for alll branches including architecture and planning branches.

So, yes csab is also for filling the vacant seats in b.arch courses.

Also check out the following link to know more about csab special round counselling :-
https://engineering.careers360.com/articles/csab-special-round-for-nits-iiits-and-gftis