With Xcode 6 GM coming out this week we couldn’t wait anymore and so pushed support for Xcode 6 into production. Now you should be able to compile and test your projects with iOS 8 SDK, including code written on Swift.
For now however Xcode 6 is still marked as beta, so you have to enable it explicitly by selecting iOS 8 SDK when configuring your project targets:
That’s all, after you save project settings new builds would use iOS 8 SDK. Please contact us at firstname.lastname@example.org if you have any problems / questions.