[saagarjha]

Mostly the latter, I would assume. Apple didn't really use anything other than Objective-C for its application frameworks (and still generally does not, for the most part).

[pjmlp]

I read in multiple sources, usually the kind of comments that is only possible to validate with inside info, that to this day not all business units are sold on Swift.

[saagarjha]

Sold or not, it's easy to see that most of the code being written is still in Objective-C just by looking at the code that Apple ships publicly.