A couple of weeks ago I predicted that WatchKit APIs woudl be Swift-only. I was wrong, at least for now – the APIs Apple released on Tuesday work with both Swift and Objective-C. But I'm not admitting defeat just yet, because these APIs aren't the whole story.
Essentially, what Apple released on this week is a way to project UI from an iOS app extension onto the Apple Watch. Under the hood, it's still mostly an iOS app. Apple says developers will be able to create "fully native apps" for the Watch starting "later next year." It's clear that the SDK for fully native Watch apps isn't finished, and that could still be Swift-only. Or, I could just be wrong. We'll probably know for sure after WWDC in Summer 2015.