Not a factory option so likely installed aftermarket or by Airstream. It does require a certified installer. Are you having issues? We have the system on our van and it is great but I did end up replacing the air system with a custom setup. The GlideRite air system got moisture in it and would drain the chassis battery. Their pump is kind of small too and would run too long. Also replaced the height control valve.
Air system upgrade starts on this page
in our build thread at the Sprinter-Source.com. Be aware that I later moved the compressor to under the hood because it was too noisy under the passenger seat.
Ride is awesome but does take some maintenance and parts are difficult to source. That's why I went with custom air system with moisture trap, larger compressor & tank plus a regulator to provide constant pressure to the bags.
WARNING! Be very careful about getting under a vehicle with air suspension. If the air pressure escapes or drops you can be crushed. Always support vehicle with jack stands.
All the best,
Hein at DIYvan