Google announced Android 4.4 KitKat two weeks back along with Nexus 5 smartphone. Google promised that Android 4.4 KitKat will also be made available to Nexus 4, Nexus 7 and Nexus 10 devices in the coming weeks. Google has started rolling the Android 4.4 KitKat updates for Nexys 7 and Nexus 10 now. Other devices that will receive KitKat update includes Galaxy S4 and HTC One Google Play edition phones.
Google announced on Google+ that Wi-Fi versions of the Nexus 7 including the old (2012) and new (2013) models and Nexus 10 will receive the update starting today. Nexus 7 3G & LTE versions will receive the update in the next few weeks.
Google Nexus devices are the first to receive KitKat updates, other manufacturers will take some time before pushing the update to their devices. HTC, Motorola and Sony already announced that their devices will receive the updates in the coming weeks to months.