Yeah, that was released with iOS 14 in September 2020. There's very little official information or documentation I can find on it, but it's mentioned here:
I wish I could adjust the curve though. It's still too white in the evenings for me.
This is part of why I wrote my own software to do this. Lifx kinda had the feature implemented (I do no like how theirs works) but also the curve was not great. Too dim in daytime, too bright at 2am.