Gmail for iOS got an update today, and the big addition in the app is the ability for Gmail to update itself in the background. The app had always been able to get push notifications, but now the app will also automatically sync all of your messages, including the read ones so they are faster to open when you launch the app. Certainly a nice feature.
The app also now allows you to sign-in to your Google account once in the Gmail app, and that sign-in will sync across all Google apps on iOS (Maps, YouTube, Chrome, Drive, etc). So, you won't have to sign-in to each app individually.
Download: Gmail for iOS
source: Gmail Blog