Thief reboot and new beta drivers from AMD are both available today
Let's get the bad news out of the way first. In a blog post earlier this week, Eidos confirmed that Thief, which launched today, doesn't have Mantle or TrueAudio support at the outset. However, support is coming soon (March), and in the meantime, AMD is serving up its Catalyst 14.2 beta drivers specifically with Thief in mind, though there are other reasons you might want to install the latest driver release as well.
In addition to updating its Crossfire profile and introducing performance improvements for Thief, AMD said it fixed some issues with Mantle in Battlefield 4 so that multi-GPU configurations (up to 4 GPUs) are now supported. AMD also added support for Frame Pacing for dual graphics and non-XDMA configurations above 2560x1600 with BF4 and Battlefield 3, and fixed a few additional issues, such as missing textures in Minecraft and corruption issues seen in X-plane.
As for Thief, minimum system requirements include a high-performance dual-core or quad-core CPU, 4GB of RAM, AMD Radeon 4800 series or Nvidia GTS 250 or higher graphics card with DirectX 10 support, and 20GB of storage space. Recommended specs include an AMD FX 8000 series or better or Intel Quad i7 Core CPU, 4+ GB of RAM, AMD Radeon R9 series or better or Nvidia GTX 660 series or better graphics card with DirectX 11 support, and 20GB storage space.