I’m never one to discourage needless bike upgrades  but they do make 9sp Shimano Shadow Plus derailleurs if you just want to change out the derailleur. Technically a 10sp derailleur should work in a 9sp system but the slightly narrower 10sp chain could cause issues on a 9sp cassette. Derailleurs are ‘dumb’ devices that move a specified amount when the cable is pulled/released by the shifter. So as long as the cable pull ratios are the same they don’t care how many gears the cassette has.
 but they do make 9sp Shimano Shadow Plus derailleurs if you just want to change out the derailleur. Technically a 10sp derailleur should work in a 9sp system but the slightly narrower 10sp chain could cause issues on a 9sp cassette. Derailleurs are ‘dumb’ devices that move a specified amount when the cable is pulled/released by the shifter. So as long as the cable pull ratios are the same they don’t care how many gears the cassette has.
Also, I believe the Shimano 11sp MTB systems are compatible with 10sp hubs. So you should be able to install an 11sp cassette on the Cross Current. It’s the road bike stuff that requires a wider rear hub to run 11sp (I know this from personal experience on my road bikes.)
https://www.google.com/search?q=shi...&ved=0ahUKEwi4m8P_yYDaAhXqh1QKHbsuBq0QgTYIxAQ
	
		
			
		
		
	
				
			Also, I believe the Shimano 11sp MTB systems are compatible with 10sp hubs. So you should be able to install an 11sp cassette on the Cross Current. It’s the road bike stuff that requires a wider rear hub to run 11sp (I know this from personal experience on my road bikes.)
https://www.google.com/search?q=shi...&ved=0ahUKEwi4m8P_yYDaAhXqh1QKHbsuBq0QgTYIxAQ
			
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