The early phase of an ultra-relativistic heavy ion collision is characterized by non-equilibrium gauge field dynamics. In particular, chromo-Weibel instabilities have been proposed as collective phenomenon that may thermalize a weakly coupled non-Abelian plasma. In this context, I will discuss analytical and numerical progress based on the Color Glass Condensate effective theory that assumes an very anisotropic initial energy momentum tensor. Recent work involves the novel incorporation of fermions in the Yang-Mills evolution of this QCD system.