PC Gamer has revealed the AMD Mantle PC update for Thief is coming March 28th.
Also announced alongside the Mantle update. AMD and Eidos are also releasing the TrueAudio patch which utilises the graphics card to offload audio effects from the CPU.
This is the 2nd game to be released with the Mantle update which saw significant framerate improvements to Battlefield 4. You can read our Thief review here.