Yes, it's happening. Dot. Gif. Android apps are finally getting state backup in the new "M" version of the OS. The full details are here. The short of it is that Android apps will now automatically back up to Google Drive, up to 25MB per app, with no new code required from developers. This is huge.

What's backed up? Settings and app data, which is to say, basically everything so long as you're not talking about something over 25MB in total size. While this may still mean signing into your apps on a new device depending on the app's security, once you do log in, the concept here is that all your settings and saved app data should just reappear on your new device. Which, holy cow, haven't we been asking for this since the beginning of time?

We haven't seen the feature in action yet, and the documentation does make it clear that while automatic backup (which happens every 24 hours) is universal on Android "M," developers can write in code to opt-out of certain parts of it, or opt their apps out of it entirely. Some apps may require specific code if they want to include app data that the new auto-backup tool doesn't natively recognize as needing to be backed up, but hopefully such cases won't be terribly common. It also sounds like apps will have to be able to target the "M" SDK level to utilize this feature, but that's obviously the case with any new API introduced with a new Android version. And, of course, most regularly-updated apps are going to write in that compatibility anyway, meaning there shouldn't be any extra work to do beyond getting your app ready for Android M.

Either way, this sounds amazing, and I have no idea why Google left it out of the keynote.

Source: Android Developers