A recent patch to rise of the Tomb Raider has included support for DirectX12, a newer graphics API with additional functionality over DirectX11, and better threading of certain aspects such as draw calls. Users are reporting mixed results- while some report better performance, many also are experiencing worse performance. From the results I’ve seen, it seems that those experiencing CPU bottlenecks experience better performance on DX12, while those with GPU bottlenecks are experiencing worse performance in DX12.
It has been noted that SLI and Crossfire are not supported by the DX12 client in Rise of the Tomb Raider. If you utilize a multi-GPU setup, it is likely better to run the game in DX11. NVIDIA users also sometimes report that the game will not display anything when running in DX12, or may experience freezing. NVIDIA also recently released a driver that caused a multitude of issues, so it is possible that these issues may be caused by that driver. AMD users, on the other hand, seem to not be experiencing these issues.
Rise of the Tomb Raider’s DX12 also adds an NVIDIA-exclusive graphics effect known as NVIDIA VXAO. VXAO is a highly complex Ambient occlusion technique that provides heavy detail, at the cost of performance. This effect can only be turned on if you’re using an NVIDIA GPU with Maxwell architecture, which includes the GTX 900 series, and the Titan. Ambient occlusion works by placing shadows around the edges of objects, creating a sense of depth within the scene.
NVIDIA’s VXAO places a heavy strain on performance, so it comes at a cost, even for those that have a GPU that supports it.