On September 24, 2012, an unauthorized patch to Thief 2 was released anonymously on the French fan site Ariane4ever. The patch updated the game to version 1.19 and used a modernized engine known as “New Dark”. Notable improvements over the legacy Dark Engine are:

• Added hardware-rendered windowed mode.
• Added single display mode option — no resolution change between menus and game.
• Added ingame support for all common resolutions, including widescreen.
• Added support for 32-bit color.
• Textures can now be automatically promoted to 32-bit, improving quality and effectively eliminating the palette limit.
• Added UI framerate cap option to avoid GPU fan spinning up in UI.
• Added DDS/PNG image support.
• Added full 24/32-bit TGA/BMP image support.
• Increased various hard-coded limitations.

There is also a compatibility mode that allows Thief Gold missions to be played with the new engine.