DirectX 12 Multi-GPU support is being released as a preview through the dx12_mgpu_preview branch on steam.
We feel that it is in a state where we can release it to you, but we are aware that some systems might still experience issues.
Please let us know when you are experiencing issues.
To activate Multi-GPU DirectX 12 you are required to do the following:
Within your Steam Library, right-click on Deus Ex: Mankind Divided.
Select ‘properties’ from the context menu and navigate to the Beta tab.
From the dropdown menu, select dx12_mgpu_preview then close the window.
Known Multi-GPU DirectX 12 issue:
Some systems may experience some graphical corruption.
The update will be applied by Steam automatically when you next start the game.