Hi there,
Sorry if this has been discussed before. I’m on my way to building a 1×11 xt set up. I have a sunrace cassette with a 46 tooth. Will the shorter gs M8000 rear mech work with the 46 tooth on the cassette? Has anyone tried it and to what effect? I have always ran medium/short xt mechs on my 9 speed setups with a 34 large tooth coupled to triple chainrings on the front and have had no bother. Advice will be greatly received.

GS is for 1×11
SGS is for 2×11

GS and SGS are both fine for 11-46 in 1×11 setup (GS has 39t capacity). You can see the specs at Shimano Productinfo which tells you all the workable options.
Both support 2×11, and both only allow 11-42 in 2×11 configuration with 10 tooth difference up front.
SGS also supports 3×11 with 11-40 and 18 tooth difference up front.

Will work fine. I’m running a 36t chain ring and 11-46 Cassette, with the short cage mech. I wouldn’t use the long cage as would be catching everything near the ground.

Will the XTR m9000 rear mech work with the 11-42 XT AND /OR 11-46 SUNRACE cassetes?

Definitely works. XT M8000 GS with SunRace 11-46 working perfectly on a 26 inch bike. It even works fine when covered in mud – which happened on it’s first ride last weekend.

Unlike the Shimano M8000 cassettes (11-42 and 11-40) I’ve had on that do not work correctly as in they won’t back-pedal in 1st.

The SunRace… back-pedals all day long. Even I don’t need that much back-pedal 🙂 It makes such a difference then things actually work the way they should though. Especially in the winter when it’s tough climbing on natural trails.

My chain line is approx 49mm. Chain stay 436mm. Rear travel 160mm.