Brando himself told us about it on the cosmere sub:

https://redd.wereii.cz/r/Cosmere/comments/1qps9wy/update_from_brandon/

Update From Brandon

Hey, all! News has broken. Rather than post on all the threads, I figured I would do a new post here with some info and thoughts.

In May I flew to Hollywood to start looking for a new partner on the Cosmere. This is something I've done before, but this time it was different. I'd been off the market for many years, working with Epic and my friends there.

That means this was my first time being in Hollywood with my Cosmere rights since...oh, 2016?

This time, I got to meet the real decision makers. Not just producers or low level executives. And this led to some really tough choices. I got the red carpet treatment, and liked everyone I met.

The decision to pick Apple was due to two factors. First, the level of approvals and control. Apple wants to be a true partner with me, and they feel like they really get what I want to do. Second, their track record. Apple does fewer things, but with higher quality, than some other studios. I find virtually every thing of theirs I watch is excellent and creator driven.

Join me for a livestream on Friday, probably 6pm mountain. I'll talk more then. But I will be writing the Mistborn screenplay myself over the next 5 months, as my full time work. Goal is for a theatrical Mistborn, then Stormlight show after. Focus on doing it carefully and right.

I promise not to get too distracted to do books. However, if I want this done right, I need to give some real attention and heart to it now.