This is a Camelbak Hydration Pack known as the Sabre, model 1744001000.
When water is all you need the Sabre is a perfect minimalist solution for daily hydration. Quick-Release shoulder harnesses ensure fast removal as necessary" and the included 2.5L" 85oz Mil Spec Crux Reservoir delivers 25% more water.
Features:
Rear Reservoir Access Flap
Front Zip Pocket Holds Your Small Essentials
Ideal for Light and Fast Jobs