We compare the magnitudes of the 2016 7.8 Kaikōura and 2010 7.1 Darfield, New Zealand, earthquakes with the magnitudes estimated for the respective earthquake sources from recently published scaling relationships that provide estimates of magnitude as a function of slip rate in addition to rupture length (Anderson et al., 2017). In this test using data that were not considered when the model was developed, we find that these new relationships provide a range of magnitude estimates that are within 1.0 standard deviations of the observed magnitudes of the earthquakes (estimated 7.75–8.03 vs. observed for Kaikōura and estimated 7.17–7.28 vs. for Darfield). Although both earthquakes involved a complex rupture process (especially the Kaikōura earthquake) and the Darfield earthquake occurred on a previously unknown fault with a very long recurrence interval, the earthquake magnitudes are consistent with the Anderson et al. (2017) models. Thus, we consider the new scaling relationships for strike‐slip earthquakes to be suitable candidates for use in seismic hazard source model developments in New Zealand while acknowledging that the evaluation is based on just two major earthquakes. We expect the scaling relationships to be part of the ensemble of inputs to the next version of the national seismic hazard model for New Zealand, which will be applied to myriads of applications in engineering, planning, and risk analysis.