Abstract: The challenge of determining whether gravity is quantum has long been hindered by the inaccessibility of the Planck scale and the difficulty of manipulating large quantum states. We propose an alternative approach that circumvents these challenges by focusing on the motion of a classical probe. We demonstrate that if gravity is classical and local, its interaction with quantum matter must induce measurable diffusion in a probe’s motion. This effect, requiring only precise tracking of the probe’s center-of-mass, offers a practical and experimentally accessible signature of classical gravity coupling to quantum matter