Necromancers,
As preparation to the launch of the free expansion at the this month I've made a beta branch available, it is feature complete but might contain some small issues. To switch to the beta branch right click on the game in library and select Properties, then choose the beta:
The game will briefly update and the new version will be available. Old saves are compatible, but I recommend starting a new game - you will be able to continue playing once it fully launches too.
Cheers,
Egi