The G280 is basically a Gulfstream G200 with a T-tail. However, Gulfstream designed the aircraft under a new type certificate. Other notable differences compared to the IAI1126/G200 are two more cabin windows on each side, in between the emergency exit and the engines, and the larger wings with taller winglets. Especially the short landing gear legs inherited from its predecessor make the G280 easy to recognise from other aircraft in this category.
Confusion possible with
As the Gulfstream G280 is essentially a Gulfstream G200 with a T-tail, without looking at the tail you can easily mix them up. Otherwise, it is easy to keep both aircraft apart.
At first glance the Gulfstream G280 and Citation Longitude are quite similar. Other than the landing gear look especially at the cabin windows, cockpit windows and dorsal fin to distinguish them.
Another close call may be with the Raytheon Hawker 4000. Though a bit smaller, the similarities are apparent. For recognition again look closely at the landing gear, cockpit windows, and the presence of winglets (G280) and fairings for thrust reversers (Hawker 4000). Note to the left on the photo is the nose of a G200!