The 2025 release of Cloudy

We present the 2025 release of the spectral synthesis code CLOUDY, highlighting the significant enhancements in the scope and accuracy of the physics that have been made since the previous release. This key development resolves the Lyman α line into ϳ-resolved fine-structure doublets, thereby making CLOUDY useful to the X-ray community. We also updated the inner-shell ionization line energies and incorporated the 1 keV feature that is commonly observed in X-ray binaries. In addition, we updated the Stout database for the carbon isoelectronic sequence, improving the CLOUDY microphysical calculations for all wavelengths. The molecular network has also been extended with new silicon-bearing species, titanium-related reactions, and phosphorus-containing molecules, enhancing CLOUDY’s ability to model the complex chemistry relevant to exoplanet atmospheres. Finally, we outline future developments aimed at maximizing scientific returns from current and upcoming generations of observatories.