For any 08+ WRX and STi any intake changes require a tune. We did testing on this a few years ago when trying out different stuff on 08+ cars and ran into it the sensitivity issue of these cars and air flow.
This dyno plot shows the AFR curve, however we ended up having to richen the car out to correct for the change in flow when we did a drop in. I dont remember exactly the #'s but it was along the line of .5-.75:1 lean out when going from OEM to drop in high flow filter.
So in a nut shell, stick with OEM air filter and airbox unless you plan on tuning for it.