Thief comes out this week (tomorrow in North America, Thursday in Australia, and Friday in Europe), and the PC version supports not only AMD's Mantle API, but also its new TrueAudio tech—or it will, anyway. Developer Eidos Montreay says it has "a little more work to do" on those features, which will be enabled in a patch scheduled for release next month. I'm not sure anyone at Eidos or AMD explicitly promised that Thief would have Mantle and TrueAudio support at launch, but I don't remember hearing anything about a planned patch, either.
In its blog post announcing the incoming update, Eidos says it's confident the patch "will ensure the best and fastest THIEF experience for AMD Radeon™ customers." Battlefield 4's Mantle implementation suffers from occasional frame time spikes, which we've observed on multiple systems, so perhaps it's best that Eidos is taking some extra time to iron out the kinks. Don't forget that BF4's Mantle patch was delayed by a month, too.
To be honest, I'm more disappointed that Thief won't provide TrueAudio support at launch. Gaming audio has been pretty stagnant in recent years, but TrueAudio could make things a lot more interesting. I'm curious to hear how it sounds, especially in a game that should reward paying careful attention to one's environment.
Today's announcement wasn't all bad news, of course. Eidos also released the official system requirements for the game, and they don't look too demanding.
OS: Windows Vista with platform update
CPU: High-performance dual core CPU or quad core CPU
RAM: 4 GB
Graphics Card: AMD Radeon 4800 series / Nvidia GTS 250
DirectX: DirectX 10
HDD/SSD: 20 GB
OS: Windows 7 or 8
CPU: AMD FX 8000 series or better / Intel Quad i7 Core CPU
RAM: 4+ GB
Graphics Card: AMD Radeon R9 series or better / Nvidia GTX 660 series or better
DirectX: DirectX 11
HDD/SSD: 20 GB
Even the 20GB install footprint seems reasonable considering the size of some other recent titles. Unfortunately, early Thief reviews haven't been overly positive. The game has a score of only 72 on MetaCritic right now.