Prison Architect Alpha 15 adds mod support29 Nov 2013
That’s not quite all, though. There are a swathe of optimisation improvements that Introversion reckon should “massively improve the size of the prisons that your rig can cope with”, as well as a staff fatigue model, which means you’ll need some common rooms to de-stress your guards.
If you’ve paid your money then you can get the alpha in the usual place (either on Steam, or via the official website). Alternatively, you can have a looksee at the video below to get a better overview of these new features.