  We demonstrate the equivalence between KMOC and worldline formalisms for
classical general relativity, highlighting how the Keldysh-Schwinger in-in
formalism is contained in both of them even though the KMOC representation
conventionally leads to the evaluation of scattering amplitudes with Feynman
propagators. The relationship between the two approaches is illustrated in
detail for the momentum kick at second Post-Minkowskian order.
