Xcode 6.1 Release was released on 20 Oct 2014 and requires macOS 10.9.4+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/xcode_6.1/56841_xcode_6.1.dmg.
Release notes are located at https://developer.apple.com/library/content/releasenotes/DeveloperTools/RN-Xcode/Chapters/Introduction.html#//apple_ref/doc/uid/TP40001051-CH1-SW432.
The compilers it contains are:
- clang 6.0 (Build 600.0.54)
- swift 1.1 (Build 600.0.54.20)
- LLVM-GCC 3.5 (Build )