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nope, the cable pull ratio is mis-matched. the shifter is 10 speed mountain series so expects a 1.2 pull ratio derailleur. all shimano 9 speed rear derailleurs use a 1.7 pull ratio. see https://bike.bikegremlin.com/1278/bicycle-rear-derailleur-compatibility/#1
you will need a shimano dyna-sys 10 speed rear derailleur for that shift lever
Thank you! I do have a 10-speed matching drivetrain, but I didn't want to cannibalize an existing build. Guess I'll just go with a matching shifter and rd. Saved me the trouble of swapping out components. Thanks again.