Background: While researchers in graduate engineering education are beginning to study facets of student experiences as they relate to attrition and persistence, theoretical applications of thriving theory have not been applied to graduate education contexts. Literature addresses students who persist and those who depart, inherently making assumptions that students who persist are doing well. Purpose/Hypothesis: The purpose of this article was to understand graduate student well-being within students that persist and depart from the engineering PhD through an adapted model of the Spreitzer et al.'s Socially Embedded Model for Thriving at Work. Design/Method: Semi-structured interviews were conducted with 64 current and former engineering PhD students, representing various stages of the PhD, status of persistence, questioning departure, or having left a PhD program. Interview transcripts were analyzed using an abductive analysis approach. Results: An expanded model for thriving in graduate school was developed. While this study contextualizes the core elements of thriving theory (context features, agentic behaviors, and produced resources), we propose that the mechanisms for thriving in graduate school lie in interactions across these themes in processes we call Adapting, Internalizing, and Cultivating. We also reveal the presence of hidden competencies (from the point of view of the graduate student participants) that facilitate these transitions. Conclusion: Thriving in graduate school is an interconnected process which has not been explored in the context of engineering. This study shows how even students who persist in their degree may only be surviving, rather than thriving.