Some days ago, Google has launched Android 4.4 over-the-air (OTA) for Wi-Fi only version of Nexus 7 and Nexus 10. Google also said that Nexus 4 and Nexus 7 3G/4G version will get KitKat update soon.
Although the Android 4.4 KitKat OTA update for Nexus 4 and Nexus 7 3G/4G version is not available yet, Google has just released factory images of Android 4.4 for those devices. It means that for those who can’t wait to taste Android KitKat, you can flash Android 4.4 manually to your device. Consequently, your data will be deleted, so don’t forget to store your data on your computer or other storage device first before flashing.
Factory images are available for Nexus 4, 2012 Nexus 7 (Wi-Fi and 3G), and 2013 Nexus 7 (Wi-Fi and LTE). No factory images for Nexus 10 currently, but OTA update has been rolled out for the tablet. Download Factory Images for Nexus Devices.