Xcode 7.1.1 opens up as Xcode 7.0.1 I updated my Xcode to 7.1.1 (it said so in the Mac App Store).

When I click on "Open", Xcode 7.0.1 showed up instead of Xcode 7.1.1.

Do I need OSX El Capitan to run Xcode 7.1.1 ?

In the past, I had Xcode 7.1 Beta 2 installed, I wonder if that caused some files to be corrupted.

Seems like someone else had a similar problem here: Updated XCode to 7.0.1 via the app store but it still shows itself at 6.4 in the app and missing the new features 

The answer there recommended deleting all copies of Xcode and reinstall from scratch.

I'll download OS X El Capitan to see if it fixes it before I decide to nuke Xcode to oblivion on my computer and redownload it all again

Update 1:

Updated my laptop to Mac OS X El Capitan but didn't fix it either. Xcode still start up as Xcode 7.0.1 =/

I guess it's time to nuke Xcode.
If you are tired downloading Xcode from the App Store or searching for old Xcode.apps somewhere hidden on your volumes, go to Developer Apple Downloads, enter a valid Apple ID and password and download Xcode 7.1.1.dmg (direct link) and any other tool you need to code or debug.

Remove any Xcode.app in your /Applications folder, open the dmg and copy Xcode to your /Applications folder.