This document describes an atom interferometer gyroscope that uses spin-dependent phase shifts induced by light near a tune-out wavelength to measure absolute rotation rates. The gyroscope uses a 3-nanograting Mach-Zehnder atom interferometer with potassium atoms. It was found that measurements of the tune-out wavelength were shifted up to 213 pm from the theoretical value due to the Sagnac effect and spin-dependent vector polarizability. This large shift suggests tune-out wavelengths could enable a sensitive gyroscope. The gyroscope measures the absolute rotation rate of the laboratory in terms of the additional phase shift needed to make the measured tune-out wavelength equal to the theoretical value.