Xcode 8.3.1 Release was released on 6 Apr 2017 and requires macOS 10.12+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/Xcode_8.3.1/Xcode_8.3.1.xip.
Release notes are located at https://developer.apple.com/library/content/releasenotes/DeveloperTools/RN-Xcode/Chapters/Introduction.html#//apple_ref/doc/uid/TP40001051-CH1-SW848.
The SDKs it contains are:
- iOS 14E269
- macOS 16E185
- tvOS 14W260
- watchOS 14V243
The compilers it contains are:
- clang 8.1.0 (Build 802.0.41)
- swift 3.1 (Build 802.0.51)