At PUBMET 2025, the LUMEN data mesh framework was presented as an architectural response to a problem: scientific data locked within disciplinary silos, communities unable to share resources across domain boundaries. The architecture proposed a federation of four scientific communities – Social Sciences and Humanities, Mathematics, Earth System Science, and Molecular Dynamics – organised around data products, data contracts, and a shared discovery infrastructure, with a federated governance layer as one of its three core components.

This contribution picks up where that presentation left off. Architectural frameworks for federated infrastructures necessarily leave certain questions open: how governance responsibilities are distributed across participating communities, what mechanisms enable collective decision-making, and how community-level arrangements align with the requirements of broader infrastructural contexts such as the European Open Science Cloud (EOSC). This talk examines how LUMEN is approaching these questions in practice, and what the process reveals about the organisational dimensions of building federated open science infrastructure.

Three layers of complexity emerge.

The first is institutional. LUMEN brings together communities of different natures: research groups embedded in a large national research organisation with its own internal decision-making structures, and an independent research infrastructure with its own governance model and member network. This diversity of institutional structures makes it necessary to establish, early on, how governance decisions are made and whose mandate they carry.

The second layer is component-level. A federated infrastructure is not a single thing – it is a set of outputs, each with different institutional owners, different user communities, and different sustainability trajectories. Governing the federation means governing the relationships between these outputs. When the question of who sustains any given component after the project ends is raised, the answer is not obvious: an existing research infrastructure, the coordinating institution, an EOSC node, or some combination. Governance must accommodate this complexity while remaining actionable.

The third layer is infrastructural. EOSC integration adds external requirements – authentication, persistent identifiers, monitoring, service onboarding – that carry their own governance logic, which does not always map cleanly onto how academic communities organise themselves.

Rather than waiting for these questions to resolve before acting, the LUMEN governance community is building iteratively: a cross-institutional task force meeting regularly, internal alignment sessions across workstreams, and a stakeholder panel planned for autumn 2026 to bring in expertise from distributed and federated platform communities. Data contracts – already piloted across five communities – serve as the first concrete instrument: making expectations explicit, establishing accountability, and providing a shared language across communities with different cultures and institutional backgrounds.

This talk presents the LUMEN case not as a model but as a worked example of what federated governance looks like from the inside – and an invitation to the PUBMET community to share how similar challenges have been approached elsewhere.