It's still Lollipop, but this update will improve stability and performance.



From ArsTechnica:

After prematurely launching an Android One site with tons of references to Android 5.1, Google has finally announced Android 5.1 via its official Android blog. It looks to be a minor update, with Google saying it "improves stability and performance" over 5.0.

The update isn't all bugfixes though. Android 5.1 adds support for multiple SIM slots and HD voice. There's also a new security feature called "Device Protection," which will lock a lost or stolen device until the user signs in with their Google account—the lockout even survives a factory reset.

We'll dive in as soon as we get a copy. Google has only said it is "rolling out" 5.1; the company didn't say where. We'd imagine it will hit AOSP and Nexus devices soon.

  Google officially announces Android 5.1