Xcode 9.3 Beta 3 was released on 20 Feb 2018 and requires macOS 10.13.2+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/Xcode_9.3_beta_3/Xcode_9.3_beta_3.xip.
The SDKs it contains are:
- iOS 15E5189d
- macOS 17E160d
- tvOS 15L5186d
- watchOS 15T5187d
The compilers it contains are:
- clang 9.1.0 (Build 902.0.34)
- swift 4.1 (Build 902.0.41)