CD Projekt Red accidentally released the mod toolkit for The Witcher 2: Assassins of Kings for a brief moment in time due to a mistake by CDPR. Community manager Marcin Momot has stated that they were “running some tests on the website” and as a result the modkit “went public for a brief moment.”
However, Momot has told members of the community who are able to grab the modkit to “have fun” since the files were official. The modkit is slated for release soon, although an official release date has not been announced.
Source: Edge Online