In the current scientific and political discourse surrounding the transformation of the scientific publication system, significant attention is focused on Diamond Open Access (OA). Diamond OA is characterized by no charges for readers or authors and relies on monetary allowances and voluntary work. This article explores the potential and challenges of Diamond OA journals, using Germany as a case study. Two key questions are addressed: first, the current role of such journals in the scientific publication system is determined through bibliometric (...) analysis across various disciplines. Second, an investigation is conducted to assess the sustainability of Diamond OA journals and identify associated structural problems or potential breaking points. This investigation includes an in-depth expert interview study involving 20 editors of Diamond OA journals. The empirical results are presented using a landscape map that considers two dimensions: 'monetized and gift-based completion of tasks' and 'journal team size.' The bibliometric analysis reveals a substantial number of Diamond OA journals in the social sciences and humanities, but limited adoption in other fields. The model proves effective for small to mid-sized journals, but not for larger ones. Additionally, it was found that 23 Diamond OA journals have recently discontinued their operations. The expert interviews demonstrate the diversity within the landscape and the usefulness of the two dimensions in understanding key differences. Journals in two of the four quadrants of the map exemplify sustainable conditions, while the other two quadrants raise concerns about long-term stability. These concerns include limited funding leading to a lack of division of labor and an excessive burden on highly committed members. Gift-like contributions, while appealing, also present challenges as potential donors not only decide whether to contribute but also how to contribute, potentially creating friction between the gift and the journal's requirements. Furthermore, journals in the lower right quadrant often rely on third-party funding, necessitating a transformation once the funding expires. Common pathways for sustaining operations include lobbying for funding at the journal's home institution or increasing reliance on gift-based completion of tasks. These findings underscore the need for the development of more sustainable funding models to ensure the success of Diamond OA journals. (shrink)