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Is it Ryzen as in mainstream desktop Ryzen or Ryzen Threadripper?
Probably all of them... as it is just slapped on top of the CPU die which is shared across all of the desktop ryzen CPUs (but not the APUs).

Also they were pretty focused on marketing it as a gaming feature as they showed it resulting in about a 12% FPS increase during the show for gears 5 I think it was and a varied but respectable uplift for several others also.
 
So, my B450 will get another BIOS for new stacked chips. Best time for an upgrade would be next year when Zen 4 comes out and "stacked" Zen 3 gets cheaper. And all the chip shortage ends.