The Budapest Open Access Initiative (2002) advocated for a new generation of journals that would rely on alternative sources of funding to support Open Access (OA) dissemination. Author fees or article processing charges (APCs) have now become one of the most common sources of funding for OA journals. These APCs dominate the public discourse surrounding financial models of OA, ultimately contributing to increased inequalities among researchers. Diamond OA, a model in which scientific publications are free for both authors and readers, is an alternative to APCs. Given their lack of indexing in major bibliographic databases such as Web of Science (WoS) and Scopus, it remains a challenge to assess the uptake of diamond OA. This paper aims to provide a global picture of the current adoption of diamond OA journals based on their coverage in various data sources. Results show the low coverage of diamond OA journals by both WoS and Scopus and the higher coverage of diamond OA in OpenAlex, as well as the generally smaller and local scope of those journals. This highlights the importance of having inclusive databases—such as OpenAlex—to increase the visibility of journals using this model.