We don't have final specs for the game yet, but I can safely say that because of the big jump in graphics and AI it will be more demanding than Gold. Our goal is to support Windows XP, ~2 GB of Ram and Direct 9c (Shader 3.0), but to get the best settings you'll need a 64 bit, dual-core system with 4 GB of ram and 512-1gb graphics card.
I can say the current version will run on relatively low end ultrabooks, but we haven't gotten into serious optimization work yet so we'll know more as we get closer to release.