Xcode 9.1 Beta 1 was released on 27 Sep 2017 and requires macOS 10.12.6+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/Xcode_9.1_beta/Xcode_9.1_beta.xip.
The SDKs it contains are:
- iOS 15B5066e
- macOS 17A360
- tvOS 15J5559d
- watchOS 15R5823b
The compilers it contains are:
- clang 9.0.0 (Build 900.0.38)
- swift 4.0.1 (Build 900.0.66)