SRAM really stepped up the derailleur game with their XX1 offering.

The heart of this derailleur is the X-horizon technology. This basically means that the parallelogram moves horizontally rather than on a downward angle like every other derailleur. Why is this so much better? Because it isolates the shift motion from riding forces. When hitting a bump, a traditional derailleur will want to move towards the wheel, resulting in ghost shifting. Another benefit of the parallelogram only moving horizontally is that if you do hit the derailleur on an obstacle, the derailleur naturally pushes out of the way, instead of twisting like a standard rear mech. The XX1, is solid as a rock! This design coupled with the Type 2.1 Roller bearing clutch massively reduces chain slap too. 

The XX1 Jockey wheels run ceramic hybrid bearings and are housed within a carbon fibre cage. The 12t X-Sync Pulley wheels utilise SRAM's patented narrow/wide chainring technology to make this the most secure system going around.

It tips the scales at a featherweight 245g.