Upvote:0
Rule of thumb, declarations are made to customs, after passport control.
If you're changing airports in Istanbul, ie from IST/LTFM to SAW/LTFJ, you'll be going though customs. Then you will need to declare.
If you're remaining in the same airport transit area, you won't need to declare.
Upvote:1
If you remain in the transit area:
You are checked in for both flights
You donβt need to re-check your luggage
you wonβt pass customs so you donβt need to declare it in Istanbul.