It is functional regardless of OS.

> Intel AMT uses a hardware-based out-of-band (OOB) communication channel[1] that operates regardless of the presence of a working operating system. The communication channel is independent of the PC's power state, the presence of a management agent, and the state of many hardware components such as hard disk drives and memory.

> Almost all AMT features are available even if the PC is in a powered-off state but with its power cord attached, if the operating system has crashed, if the software agent is missing, or if hardware (such as a hard drive or memory) has failed.

— https://en.wikipedia.org/wiki/Intel_Active_Management_Techno...