Next-generation gravitational wave detectors require highly precise predictions for the waveforms. New advances in understanding binary inspiral dynamics have been achieved by taking classical limits of scattering amplitudes in perturbative quantum gravity. I present our recent new work on the effects of black hole spin at the 3rd order in the gravitational constant, obtained from a 2-loop scattering amplitude involving massive spinning particles. The calculation of the amplitude is based on modern methods including numerical unitarity, integration-by-parts reduction, and differential equations. We take two complementary approaches to extract classical physics from the amplitude, including non-relativistic effective field theory and the Kosower-Maybee-O'Connell formalism.