Digitalization drives societal transformation to reform existing practices in the evolving environment. Central to this transformation is the creation of interoperable digital public services across diverse organizations, increasingly guided by human-centric principles and life-event orientation. This paper explores the complex process of achieving digital service innovation, emphasizing the need for inter-organizational balancing between radical transformation and efficiency through collective ambidexterity, where multiple ecosystem actors coordinate to balance innovation and efficiency simultaneously. While previous research predominantly studied ambidexterity at the organizational level, focusing on its antecedents, mechanisms, and outcomes, our study extends this inquiry to the broader ecosystem. Via a single-case study, we investigate how collective ambidexterity can be governed in a large-scale digital service ecosystem. To address the research question, we developed a multi-level conceptual model of governing mechanisms, antecedents, and outcomes of collective ambidexterity across three analytical levels: the ecosystem, organization group, and organization. Our theoretical contribution is twofold. First, we enhance conceptual clarity on collective ambidexterity and show how Modes of Collaboration (MoC) can facilitate innovation and efficiency of human-centric digital services throughout the three levels of governance. Second, the resulting governance model emphasizes the need to connect centralized, decentralized, and group-level governance strategies for developing digital services—to achieve and govern collective ambidexterity in the development of digital services in the public sector.