Wilson to Lindblad: Late-time Obstacles to Reliable Calculations with Horizons (and how Open EFTs can help). This talk describes how Open Effective Field Theories can be used to deal with the break-down of perturbative methods at late times by working to all orders in g^2 t as the coupling g goes to zero while t goes to infinity. The method is illustrated using the late-time behaviour of a qubit (or Unruh detector) interacting with a quantum field in various spacetimes, showing how to calculate the thermalization and decoherence times that describe its relaxation towards a thermal final state.