SRAM XO1 is closely related to XX1 which has taken the mountain bike world by storm. XO1 has a 94mm bolt circle diameter compared to XX1's 76mm. This means the XO1 might be considered slightly stronger but the smallest ring available is a 30T so stick with XX1 if you want or may want to use a 28T chainring. Because of the different bolt circle diameters, XX1 rings are not compatible with XO1.
Like XX1, XO1 uses carbon arms and an alloy spider. A SRAM PC-XX1 chain is recommended. Chainrings are sold separately so you can pick the ideal ring to match your fitness level and riding you have in mind.
SRAM single ring mountain groups provide a host of benefits with virtually no drawbacks. Both weight and cost are reduced by eliminating the need for a front shifter and derailleur. Chain drop is taken off the table thanks to X-Sync tooth profile.
SRAM engineers looked into the causes of chain drop and video analysis showed side to side movement was the main culprit. They came up with a CNC-machined, wide tooth, narrow tooth pattern which perfectly mates with the XX1 chain for a snug fit with slight taller, squared-off teeth.
Chainring and bottom bracket bearings not included - available separately