<p>Digital platforms rely on third-party complementors to create and sustain value over time. While early research has emphasized platform strategies to attract and onboard complementors, less is known about how complementors sustain their engagement with a platform after the initial product launch. We conceptualize complementor engagement as sustained, behaviorally enacted involvement in a platform and examine how ongoing product enhancement activities—specifically, routine maintenance and adaptation to platform-wide changes—act as observable manifestations of this engagement. Focusing on product complexity arising from the addition of features, which is facilitated by the unique characteristics of digital platforms, we investigate how complexity influences the sustained engagement behaviors of complementors. Using a multimethod approach that combines longitudinal panel data from the Apple iOS App Store with a randomized experiment, we find that more complex products are associated with more frequent product maintenance, indicating stronger ongoing engagement at the product level. At the same time, while the experimental participants perceive higher product complexity as substantially constraining their ability to adapt quickly to platform-wide changes, archival evidence reveals that complexity does not slow complementors’ actual adaptation in practice. This difference between perceived difficulty and enacted behavior provides an important insight into how complementors navigate real market incentives, development capabilities, and platform governance when responding to platform evolution. Collectively, our findings clarify how product complexity shapes sustained complementor engagement and contribute to research on digital product strategy, platform governance, and the behavioral foundations of engagement in digital platform ecosystems.</p>