The Hamburg State and University Library (Staats- und Universitätsbibliothek Hamburg) provides with Hamburg University Press an established Institutional Publishing Service Provider (IPSP) in the Hamburg metropolitan region. Among other open access publication services, Hamburg University Press offers the hosting of Diamond Open Access journals with the open source software Open Journal Systems (OJS). The service's basic idea emerged from the Hamburg Open Science Framework, funded by the Free and Hanseatic City of Hamburg, and the associated project Modern Publishing. The project's outcome was a professional state-of-the-art hosting service. Now in regular operation, the Diamond Open Access hosting is a standardized scholar-led service. This is based on clear formal and technical standards as well as on policies which derive from international requirements and recommendations (e.g. Plan S, DOAJ, OpenAIRE). In addition, the service is closely linked to the ongoing European projects CRAFT-OA and DIAMAS. The standards apply to the journals as well as to the service as whole. Researchers are supported in publishing scholar-led and quality-assured articles and journals. As a result Hamburg University Press provides a professional hosting service that is sustainable, scalable, and resource-efficient. Upscaling services like the described hosting service keep pace with the dynamics of the scholarly communication ecosystem and can respond to evolving needs of technology, policies, and especially research. With this poster we will explain the concept of Hamburg Universits Press' Diamond OA journal hosting. This poster has been accepted for the poster session of the endorsers of the Action Plan for Diamond Open Access on the occasion of the Global Summit on Diamond Open Access, Toluca, Mexico, 23-27 October, 2023.