  Crossover quintessence predicts that the time variation of fundamental
couplings is substantially faster at redshift $z\approx 2$ than over the past
few billion years. This could reconcile the reported time variation of the fine
structure constant from quasar absorption lines with severe bounds from
archeo-nuclear physics and high precision tests of the equivalence principle.
We present a model that is consistent with all present data on time varying
couplings, tests of the equivalence principle and cosmology.
