From the Wiki article: American aeronautical engineers dispute this, pointing out that as is the case with the MQ-1 Predator, the MQ-9 Reaper, and the Tomahawk

From the Wiki article: American aeronautical engineers dispute this, pointing out that as is the case with the MQ-1 Predator, the MQ-9 Reaper, and the Tomahawk, "GPS is not the primary navigation sensor for the RQ-170... The vehicle gets its flight path orders from an inertial navigation system".[20] Inertial navigation continues to be used on military aircraft despite the advent of GPS because GPS signal jamming and spoofing are relatively simple operations.