Xcode 9.4 Beta 1 was released on 2 Apr 2018 and requires macOS 10.13.2+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/Xcode_9.4_beta/Xcode_9.4_beta.xip.
Release notes are located at https://download.developer.apple.com/Developer_Tools/Xcode_9.4_beta/Xcode_9.4_beta_Release_Notes.pdf.
The SDKs it contains are:
- iOS 11.4 (Build 15F5037c)
- macOS 10.13.4 (Build 17E189)
- tvOS 11.4 (Build 15L5536b)
- watchOS 4.3 (Build 15T212)
The compilers it contains are:
- clang 9.1.0 (Build 902.0.39.1)
- swift 4.1.1 (Build 902.0.50)