A new core content pack was added in the most recent experimental.
You can find the commits related to it by just searching it on the cdda github: https://github.com/CleverRaven/Cataclysm-DDA/pulls?q=dark+skies
(Sorry if this isn’t the most direct way. If someone knows of a more convenient or official place that the commits are displayed, please tell me.)
It’s pretty cool. However, I am playing a new world with it and I just realized that I still have the default core content pack Dark Days Ahead loaded in this world. Is this okay?