macOS Mojave 10.14.2 beta 18C38b

Under normal use the AMD 560X discrete graphics chip gets all 4GB of its VRAM saturated.

AMD 560X 4GB VRAM

information gathered using iStat Menus 6.2

Temperature 113˚F

Core Clock 214 MHz

Memory Clock 300 Mhz

Memory ~3.6GB

Processor ~5%