This video shows you how to enable Nvidia Reflex on the current build of the test server in Rainbow Six Siege. Make sure you launch it in Steam and choose the Vulkan option. This is only for people who have Nvidia Graphics Cards.
NVidia reflex is on the live server. Make sure you update your NVidia drivers using Geforce Experience. And that you launch the game using Vulkan. If you still don’t see the option you may need to check with NVidia that you’re graphics card is compatible.
Download and install newest Game Ready Driver now, which is a required update for Reflex in Rainbow Six Siege, so you’re ready to roll the second it launches.