At this point you've likely "made the leap" to swipe SRAM's marketing parlance. Whether you modified a 10-speed cassette with a One-Up-style expansion cog or adopted early and wore out your first cassette the SRAM XX1 XG-1199 Cassette is the pinnacle of one-by technology. By trading freehub bodies for drivers SRAM was able to put a tiny 10-tooth cog on the end to balance out the monster 42-tooth cog on the low end. This ensures that the balance of granny grinding to flat-out-flying is maintained.