No difference outside, just the torx screw on the clutch (force 1, 1x11):
Sram says it provides a "smoother torque curve for a quieter, more consistent operation and feel".
From Mountain Biking Australia:
http://www.mtbiking.com.au/gear/sram-eagleWith the first generation Type 2 derailleurs, the clutch was often excessively tight and developed a knock that could be felt through the bike. It was then replaced by Type 2.1; a non-serviceable rendition that didn’t suffer the tightness issues but often lacked clutch force—more chain slap was usually the result. So far the new Type 3 clutch seems to have these issues sorted. The Eagle derailleur has a nice tight spring and enough clutch force to keep the chain firmly in place. When the cage does move, the action is smooth and there’s no feedback through the frame. The Type 3 clutch isn’t exclusive to the top-dollar Eagle parts either; it also features on the recently released NX derailleur and over time it will be phased in right through the SRAM range.