How do I install Xcode 9 without updating macOS?

Question

Does anyone have any idea to install Xcode 8 OR Xcode 9 without updating macOS?

I want to update my Xcode 7.1 to Xcode 8 or Xcode 9 (or 9.1) Beta.

But it is

Answer 1

From the Xcode 8 Beta 6 Release Notes:

Xcode 8 beta 6 requires a Mac running macOS Sierra beta 3 or later, or OS X El Capitan 10.11.5 or later.

macOS 10.10 is an unsupported configuration and is not supported by Xcode 8. Your only solution is to update to 10.11.