Over at its Steam page Eidos states that "Deus Ex: Mankind Divided," will not ship with DirectX 12 support at launch. The game will release on August 23, 2016 based on DirectX 11. DirectX 12 renderer will be added via a patch, which will release in the week of 5th September.

The Deus Ex franchise originated on PC, and we’re passionate about continuing to provide the best experience possible to our long-time fans and players on the PC. 

Contrary to our previous announcement, Deus Ex: Mankind Divided, which is shipping on August 23rd, will unfortunately not support DirectX 12 at launch. We have some extra work and optimizations to do for DX12, and we need more time to ensure we deliver a compelling experience. Our teams are working hard to complete the final push required here though, and we expect to release DX12 support on the week of September 5th! 

We thank you for your patience, passion, and support. 

- The Deus Ex team

No DX12 Support for Deus Ex: Mankind Divided at Launch