Study finds 440 diamond open-access journals dropped free model since 2009

A preprint led by Lisa Matthias at Humboldt University of Berlin tracked 440 academic journals that began as diamond open-access, meaning free for both authors and readers, but later shifted to charging fees between 2009 and 2026. Most of these titles, 369, moved to gold open access with article-processing charges, 52 adopted hybrid models, and 19 became fully paywalled, with fees ranging from $8 to $5,300 depending on publisher type.