What are the differences between the LSS and LSS-XL?

Both chassis are great options but offer slightly different feature sets for the shooter. 

LSS-XL Gen2 - This chassis for most inlets can be selected in the Fixed or Carbine buttstock interface.

• built-in thumb shelf 
• Fixed buttstock interface approx 12.9"
• Carbine buttstock interface approx 11.7"
• M-LOK on 5 sides of the forend. 
• Night Vision hood accessory 
• barrel size of 1.35"

LSS Gen2 - This chassis is only offered in a Carbine interface. 

• No thumb shelf
• The forend is approx 6.75"-8" depending on the inlet
• M-LOK on 3 sides
• barrel size up to 1.25"