It can be downloaded from https://download.developer.apple.com/Developer%5FTools/Xcode%5F10.2%5FBeta%5F3/Xcode%5F10.2%5FBeta%5F3.xip.
Release notes are located at https://developer.apple.com/documentation/xcode%5Frelease%5Fnotes/xcode%5F10%5F2%5Fbeta%5F3%5Frelease%5Fnotes.
The SDKs it contains are:
- iOS 12.2 (Build 16E5201d)
- macOS 10.14.4 (Build 18E194d)
- tvOS 12.2 (Build 16L5201d)
- watchOS 5.2 (Build 16T5201c)