Xcode 10.3 GM was released on 22 Jul 2019 and requires macOS 10.14.3+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/Xcode_10.3/Xcode_10.3.xip.
Release notes are located at https://developer.apple.com/documentation/xcode_release_notes/xcode_10_3_release_notes/.
The SDKs it contains are:
- iOS 12.4 (Build 16G73)
- macOS 10.14.6 (Build 18G74)
- tvOS 12.4 (Build 16M567)
- watchOS 5.3 (Build 16U567)
The compilers it contains are:
- clang 10.0.1 (Build 1001.0.46.4)
- swift 5.0.1 (Build 1001.0.82.4)