The Thief 1/2 Gold versions sold on Steam/GOG use a DX9 renderer that was originally written as a fan-mod, allegedly based on leaked source code from the Dreamcast version.
Unfortunately still no G3D since all the actual 3D calculations are done in software and DX9 is only used to draw the already transformed vertices to the screen, so no way for vorpX to create stereo images. At least that’s my working theory, tried quite a while. Sounds reasonable considering that Thief was released in the very early days of 3D gaming years before DX8/9.