Google has begun to deliver app launcher customizing in what it calls the "Google bar" to its users on Thursday.
The change affects the app grid on the top right of Google services when you're logged in. Before, the apps shown on the grid were locked into place. They included Google+, Search, Gmail, Drive, and Calendar.
If you've received the ability to customize the grid, you'll see a notification at the top of the launcher.
By placing the Google+ app at the top-left of the grid, in addition to a Google+ link next to the grid icon, Google was signaling just how much it wanted people to use Google+ more.
Some people reported their customizations not sticking in the comments on the Google+ post announcing the update, although the problem doesn't seem to be affecting all users.