This document reports on the third EOSC Winter School, organised in Nice (France) on 27–29 January 2026 by the EOSC Association (EOSC-A), with the support of the EOSC Gravity project.Building on the momentum created by the EOSC Symposium 2025 and the substantial progress achieved by the EOSC Federation Build-up Group, the EOSC Winter School 2026 among all stakeholders. The event was designed to align efforts, deepen collaboration, and ensure that all relevant EOSC structures and expert groups actively contribute to the implementation of the EOSC Federation.The Winter School was co-located with a closed meeting of the EOSC Federation Build-up Group (26–27 January 2026). The main objective of this co-located format was to ensure that Opportunity Area Expert Groups (OAEGs), EOSC-A Task Forces, and EOSC Federation Build-up Working Groups work in a coordinated and complementary manner towards supporting the EOSC Federation. This format strengthened the connection between expert recommendations and governance-level decision-making.Under the motto “Supporting the EOSC Federation”, the Winter School featured two related parts:• EOSC Stakeholder Brokerage Event (27 January): A matchmaking session that brought representatives from the EOSC Nodes in contact with potential service providers from EOSC-related projects and the broader stakeholder environment• Thematic Tracks (28-29 January): Engaging sessions dedicated respectively to the (i) Federating capabilities and interoperability, (ii) resources, and (iii) competences and training related to Open Science.