Shimano 9 speed road hub compatible with XT 11 speed cassette
Changing from a 9 speed road to 11 speed mountain raises many, many questions, but answering your specific query:

An 11 speed mountain cassette will fit on a '9 speed' hub. The freehub body width used is the same for mountain 11 speed and below and road 10 speed and below. Road 11 speed cassettes generally requires a slightly wider freehub body. The mountain 11 speed cassette will fit because the larger sprockets can overhang the hub and spokes a little.