The research on sustainability transitions (ST) addresses the global sustainability challenges, underlying the importance of radical innovations in a systemic way. However, as we argue, the ST scholars tend to use the term “sustainability” without proper justification and operationalisation, often implicitly assuming that the studies empirical cases contribute to sustainability. To address this, our paper analyses this in-house assumption in the ST community and critically questions it. To bring this forward, we address the following questions (I) What ways of inquiry are likely to facilitate the development of reflections on the sustainability assumptions underlying the empirical cases in the ST literature?  (II) To which extent do the ST scholars reflect on the sustainability assumptions underlying the empirical cases they study, as expressed in their research texts?  To address these questions, we revisit the extant literature, propose a framework of six dimensions and, in turn, apply this framework on a number of systematically selected ST cases. Our study shows that the ST scholars don’t always reflect on to which extent the focal cases contribute to the transitions towards more sustainable modes of production and consumption. The alternative sustainability solutions are often overlooked; the sustainability-effects beyond the empirical boundaries are not always reflected; and trade-offs of the focal case’s contributions on (social, economic and environmental) sustainability are mostly not taken into account. Thus, we argue for the necessity of a reflexive inquiry on the future empirical studies of the ST field, as we name it case “sustainabilitiness”. If taken as a methodological tool, the proposed case “sustainabilitiness” framework suggests the primary dimensions which may be applied for the case selection, analysis and interpretation in future ST studies.