The new inbox is now the default for all users, but it's optional
The new tabbed Gmail inbox is here for everyone. For some, it may be the best feature Gmail ever introduced. For others, it may be a very annoying hindrance.Thankfully, the new inbox is completely optional and Google makes it very easy to disable it or to switch to any of the other inbox types it offers.
All you have to do is click on the "gear" settings icon and select "Configure inbox." In the dialog that pops up, you can uncheck any of the tabs you don't want.
If you uncheck them all, you will be reverted to the regular Gmail inbox where all email messages are shoved together in the order they came in.
Alternatively, you can try out any of the other inbox types Gmail offers. From the "gear" icon, select Settings, go to the Inbox type, and you'll be able to choose between Default, Important First, Unread First, Starred First, and Priority Inbox.