  We elaborate on the cosmological implications of the recently established
non-perturbative $O(D,D$)-symmetric approach. Following the $\alpha'$-complete
Friedmann equations, we provide a qualitative description of the dynamics of
anisotropy perturbations. We find that the spacetime stability depends on the
sign of the generalized dilaton time derivative. We consider isotropic limits
and find possible mechanism for pre-big bang cosmology, governed by the value
of cosmological constant.
