The new Thief is just around the corner and the guys at Eidos Montreal have announced that support for ATI's Mantle API has been removed from the game until a further patch.
Battlefield 4, Star Citizen and Sniper Elite 3 have already taken advantage of the system and Thief was set to become the next, but alas, we will have to wait.
Eidos Montreal said on their website that they're "extremely proud" of the work that they have done.
We're extremely proud of the work we've done with AMD to make the PC version of Thief a stand-out, definitive experience although we have a little more work to do to accommodate all of these new PC-specific features.
The company are working on a patch to support mantle and TrueAudio and it is set to be released around March time.
We're confident this patch will ensure the best and fastest Thief experience for AMD Radeon customers,
We’re sorry we couldn't bring this to you sooner – although we will use this time to bring you the very best experience possible and will let you know when the patch is ready.
You will of course still be able to run Thief on your AMD/ATI card - just not via Mantle, yet. There are now some revised PC requirements on the website.