Firms in open innovation ecosystems expand organizational resources and allow for collaborations across organizations, which can promote the flow, aggregation, and integration of resources within business network ecosystems. Yet, particular gaps in the literature limit our understanding of how open innovation ecosystems contribute to firm product innovation. Therefore, this study explores the causal recipes of how open innovation ecosystem modes promote product innovation by using both grounded theory and fuzzy set qualitative comparative analysis (fsQCA). First, by taking four innovative firms as case studies and applying grounded theory, we identify six specific open innovation ecosystem modes: “firm-university-institute cooperation,” “interfirm cooperation,” “firm-intermediary cooperation,” “firm-user cooperation,” “asset divestiture,” and “technology transfer.” Then, based on the data of 226 innovative firms, we employ fsQCA to explore the causal configurations of the open innovation ecosystem modes that consistently improve product innovation. The findings reveal that three particular combinations can explain the high level of product innovation: (1) interfirm cooperation, firm-intermediary cooperation, and technology transfer combined with asset divestiture; (2) interfirm cooperation, firm-intermediary cooperation, and technology transfer combined with firm-university-institute cooperation; and (3) interfirm cooperation, firm-intermediary cooperation, and firm-university-institute cooperation combined with firm-user cooperation. Overall, this work contributes to the theoretical literature on open innovation ecosystems and provides practical information for firms looking to achieve value creation.