AstroPad also had this happen to them: https://astropad.com/sherlocked-by-apple/

Apple actually bought Dark Sky, lock, stock, and barrel. (And developers.)

https://news.ycombinator.com/item?id=22739839

I have the new Weather app in iOS 15 which is the replacement for Dark Sky and they made it better. This was surprising to me.

I can't set custom alerts anymore for e.g., umbrella or UV, but the automatic alerts are exactly how I wanted them anyway... and it's nice that the app changes which data is shown based on the current conditions: if it's going to rain, the map shows weather radar instead of temperature