For more than a century, the Carnegie Unit has been the central organizing feature of American education. Translated into the "credit hour" in higher education (roughly, one hour of class time per week in a 14-16 week semester), this time-based unit is embedded in nearly every aspect of the system, from faculty-workload and cost-per-student calculations to countless student enrollment and transfer transactions. For its dominance and standardizing effect, the Carnegie Unit has been the subject of a great deal of criticism over the years. Managing and measuring everything by the same time-based standard, critics have argued, limits flexibility and obscures quality. Today, this credit-hour critique is more pointed than ever. With mounting accountability and cost pressures, critics say the Unit now stands in the way of higher education reforms that are necessary to create more accessible and affordable pathways to degree completion and, eventually, employment. Chief among these reforms is the shift to "competency-based education" models, which assess and grant credit based on learning rather than time. While it is true that the Carnegie Unit presents some real obstacles to these models (primarily through rigid federal financial-aid requirements), calls for its demise frequently overlook the Unit's significance as the only universal standard and common currency that unites our vast and varied system. This article presents an examination of the Unit's past and present that reveals much about its future utility as a platform on which innovations such as competency-based education can advance at scale.