ARPA-E aims to support the development of timely, commercially viable fusion energy. [1] Based on numerous studies examining the cost challenges facing advanced nuclear energy, [2] which shares some attributes with fusion such as unit size, capital cost, and power-generation characteristics, ARPA-E believes that a commercial fusion power plant should target an overnight capital cost (OCC) of <US$2B and <$5/W. [3] If a grid-ready fusion demonstration can be realized within approximately twenty years while satisfying these cost metrics, then, as a firm low-carbon energy source, fusion can contribute to meeting global, growing low-carbon energy demand and cost-effective deep decarbonization [4] in the latter half of the century.