  We argue that the tree-level graviton-scalar scattering in the Regge limit is
unitarized by non-perturbative effects within General Relativity. At Planckian
energy the back reaction of the incoming graviton on the background geometry
produces a non-perturbative plane wave which, in turn, softens the UV-behavior.
Our amplitude then interpolates between the perturbative graviton-scalar
scattering at low energy and scattering on a classical plane wave in the Regge
limit.
