In 2015, M. Canadell and R. de la Llave consider a time-dependent perturbation of a vector field having an invariant torus supporting quasiperiodic solutions. Under a smallness assumption on the perturbation and assuming the perturbation decays (when t → +∞) exponentially fast in time, they proved the existence of an asymptotic KAM torus. An asymptotic KAM torus is a time-dependent family of embedded tori converging in time to the invariant torus associated with the unperturbed system. In this paper, we generalize this result in the particular case of time-dependent Hamiltonian systems. The exponential decay in time is relaxed (due to the geometrical properties of Hamiltonian systems) and the smallness assumption on the perturbation is removed.