Auslander conjecture for compact flat pseudo-Riemannian manifolds

Let $M$ be a compact pseudo-Riemannian manifold of constant sectional curvature $0$.

Auslander conjecture, special case. The fundamental group $\pi_1(M)$ contains a solvable subgroup of finite index.

This is the pseudo-Riemannian analogue of the Bieberbach theorem for compact flat Riemannian manifolds. The source states that the analogous result was still unknown, so the conjecture remains open.