Replacing crank rings 26/36/48 on XT T8000 with 22/30/40 SLX M7000 Are the crankrings interchangeable, will XT front derailleur work?
Bike set up all XT components. Want to improve gear inches. XT is not offering smaller crank rings.

The bike is all T8000 components. I will check for M8000 dérailleur.
I am assuming the chain ring are compatible.
If your bike came with those ring sizes, it probably has one of the trekking type front derailleurs. Find its model number on the back side of the cage and look up its specs to corroborate. Using this type of FD with a 40, 42, 44 etc will create excess gap with the cage that may result in chain drop and/or mediocre shifting. To avoid this, switch to a non-trekking 11s triple Shimano mountain FD.
If 30/40 is what you're after, double check compatibility for the FD in question with the minimum middle to large difference spec. Your resource for those numbers is si.shimano.com.