Google has started rolling out the recently-leaked Google Play device client version 4.4, which brings slide-out (hamburger) navigation. There don’t seem to be many changes and as no official change-log is available right now, we can’t be sure about any under-the-hood tweaks (if there are any).
With the new update, Google Play device client is now in sync design-wise with other Google applications like Gmail, Keep, and Drive etc. As these updates are released in batches, it might take hours to days for this update to reach your Android devices.
You could install one of APKs floating around but it is always better to wait for the official version to automatically reach your device.