Samsung Galaxy S3 and S3 Mini will not get KitKat
Samsung Galaxy S3 and the Samsung Galaxy S3 Mini launched loaded with Android 4.0 and their hardware specs allow both of them to properly run Android 4.4 KitKat. Unfortunately, while stock KitKat supports devices with 512 MB of memory, Samsung claims its TouchWiz UI customization requires no less than 2 GB to run in optimal conditions.
SamMobile recently received an official statement from Samsung Mobile UK that says "Samsung has decided not to roll-out the KitKat upgrade to Galaxy S3 and S3 mini 3G versions, and the KitKat upgrade will be available to the Galaxy S3 LTE version as the device’s 2GB RAM is enough to support the platform upgrade."
While Samsung claims the Galaxy S3 and S3 Mini "cannot effectively support the platform upgrade while continuing to provide the best consumer experience" it would not be a surprise to see unofficial KitKat updates that work as intended showing up soon. Unfortunately, less adventurous users who only update their handsets via the official channels will have their devices stuck to Android 4.3 (Galaxy S3) and 4.2 (S3 Mini).
Samsung Galaxy S3 variants with 2 GB of memory should get their KitKat update soon, as Sprint already started rolling it out for its Galaxy S3 handsets.