The Pingo STARR project has undertaken a large geophysical study of Arctic pingos designed to investigate their internal structure and evolution over time. GPR surveys of thirteen pingos reveal significant variability of internal architecture despite similarities in surface morphology. Of the thirteen pingos, only two show evidence of the well-developed massive ice core that is predicted by the classic model of pingo formation. These results call for a new, more nuanced approach to understanding pingo formation and evolution.