Q. Do I need an RDS license if I enable RemoteFX on my Windows VDI VMs?

A. Yes. RemoteFX is a component of RDS, so if you use RemoteFX, you need an RDS CAL. This is the same as any time you use an RDS component, which includes the RDS Virtualization Host you typically use with VDI environments anyway. Also remember that Microsoft VDI suites include the RDS CALs required to use all the RDS-related functionality in a VDI environment, including RemoteFX.