Xcode 9.3 Beta 2 was released on 6 Feb 2018 and requires macOS 10.13.2+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/Xcode_9.3_beta_2/Xcode_9.3_beta_2.xip.
The SDKs it contains are:
- iOS 15E5178d
- macOS 17E150d
- tvOS 15L5175d
- watchOS 15T5176c
The compilers it contains are:
- clang 9.1.0 (Build 902.0.31)
- swift 4.1 (Build 902.0.38)