Abstract: We consider the Klein-Gordon equation on Minkowski space with a class of space-time potentials that decay sufficiently fast in spatial directions and approach a limiting potential as t → ∞. Building on previous work of Vasy for many-body scattering problems, we show that the Klein-Gordon operator admits a description as a non-elliptic Fredholm operator as a map between anisotropic Sobolev spaces. The talk is based on joint work with Dean Baskin and Jesse Gell-Redman