Context: The adoption of Open Source Software (OSS) in Public Sector Organizations (PSOs) is on the rise, driven by benefits such as enhanced interoperability and transparency. However, PSOs encounter challenges stemming from limited technical capabilities and regulatory constraints in public procurement.

Objective: This study, based on a registered report, explores the organizational aspects of development in public sector OSS projects, i.e., projects initiated, developed, and governed by PSOs. We conjecture that the development diverges significantly from the commonly adopted bazaar model, wherein development is carried out collaboratively within a broader community.

Method: A purposefully sampled set of six public sector OSS projects was investigated using mixed-methods and compared with previously reported cases of bazaar OSS projects.

Results: Among the cases, we note that most (80%) of development efforts typically involve a small group of developers (<15) and rely on formalised processes. Developers are commonly procured from national and local service suppliers. Projects are planned top-down by involved PSOs with funding and contributions to development enabled through centralized or decentralized sponsorship. Projects with a centralized sponsorship have one or a few main PSOs funding the major part of the development. Decentralized sponsorship implies multiple PSOs being mutually dependent on each other to pool the necessary resources for the development. All OSS are reported as being of high quality despite limited size and contributions from their communities.

Conclusions: Findings suggest that public sector OSS projects deviate from the typical bazaar model, highlighting the need for tailored approaches to address challenges and solutions specific to their context.