How to install Xcode 6? I just got myself a MBA and I am wondering how do I install Xcode 6 on my MBA?

In the Mac App Store I can see Xcode 5.1.1 so I have started installing that on the MBA. But, I want to install Xcode 6 and more specifically Swift. How do I do that?
Xcode 6 currently requires an active iOS or Mac Developer Program membership, available from developer.apple.com/programs, as Xcode 6 and Swift is not publicly available yet.  Once Xcode 6 is out of beta / prerelease anyone should be able to download it from the MAS, but that is speculation based on past experience and not something Apple has announced.