The X99 platform can accomodate up to 16gb DIMMs.  The X99 Classified and FTW both have 8 DIMM slots equaling 128GB, and the Micro having 4 DIMM slots can support 64gb.

The X99 boards do *NOT* support 32gb DIMMs or larger, thus meaning you cannot run 4x32gb to have 128GB of RAM, 128 is achieved ONLY through 8 16GB DIMMs.