They used to have separate 9, 10 and 11 speed drivetrains where every component was specific to the number of gears you had, and in theory you had to replace th

They used to have separate 9, 10 and 11 speed drivetrains where every component was specific to the number of gears you had, and in theory you had to replace the entire drivetrain just to go from a 9-speed cassette to a 10-speed. The CUES version has just a single chain, derailleur, crankset, etc. which all work with all three rear cassettes.