Assassin's Creed was one of the first games with support for DirectX 10.1 but Ubisoft now says they're going to remove this feature to address concerns over graphical glitches.
Of course, DX10.1 is supported primarily in ATI's Radeon 3000-class GPUs, with Nvidia choosing to eschew support for the most part, claiming that there was nothing important to be missed.
But a new graphical analysis of the game running under DX10.1, which you can see over at HardOCP here, has shown that there is actually a large performance boost to be had from a couple of the more efficient rendering algorithms in the updated spec. Author Mark Warner called the boost 'significant', pumping the frame rate up by as much as 20% with anti-aliasing enabled - although with no discernable improvement in image quality.
However, Ubisoft says that the performance gain is due to a bug in the rendering process - despite there being no visible difference in image quality - and will be promptly removing 10.1 support from the game in an upcoming patch. This seems rather non-sensical when image quality is good and there are performance improvements to be had. There is no suggestion from Ubi that there is any instability here - they are simply taking a performance boost for Radeon cards and removing it.
HardOCP's own Kyle Bennett makes what is sure to be an interesting point: Assassin's Creed is an Nvidia 'The Way It's Meant To Be Played' title, and the firm has almost certainly invested a few dollars in making sure the PC port runs well on Green Team graphics boards.