4.3, which is still part of Jelly Bean, will be a minor update ahead of Android 5.0 Key Lime Pie, which is still expected for later this year.
A welcome update (as all Nexus users can attest too) is the update to the dialer. The phone will now automatically suggest your contacts as you dial numbers, like it used to before 4.2. You currently have to type out the full number or head to contacts to search.
It is important to note that the new dialer autofill will not be turned on by default.
Additionally, the camera application will come with new minor updates. Another cool update is a setting that you can allow your Wi-Fi to be turned on to get a lock on your location before it is automatically turned off again. Apps will not send you push notifications asking you to try to hop on a Wi-Fi network anymore if you have that setting enabled.
In a move that was likely spurred by the launch of Google Glass, 4.3 devices can now utilize Bluetooth Low Energy to save battery when linked to Glass or smartwatches (for example).
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