All the support libraries are dropping the v4 v7 v12 v13 etc tags and everything is refactored into the androidx packages.
They are essentially the same but for future reference androidx will be the library that we should use in our apps.
Android studio 3.2 canary that comes out this week (week of May 14, 2018) should have the tool that allows automatic refactoring to the androidx packages. There was an announcement about this at google i/o 2018.