There is growing consensus that the role of the distribution system operator (DSO) is changing given the implications of net zero. The transition process requires additional roles for the DSO in facilitating the new technologies and business models that will contribute to decarbonization. Discussions on the active DSO abound yet a working definition is still missing. This paper aims to propose such a definition and a workable methodology for measuring the extent to which a DSO is active. The methodology will be applied to electricity and gas DSOs in the UK and the challenges will be presented and analyzed.