The rumours comes from AndroidSAS, although no source is mentioned but it is expected that Sony Xperia Z1 will be updated to Android 4.4 KitKat this November, more specifically on 7th of this month(even the date is specific).
Precisely this isn’t going to happen, the best Sony can provide to their Xperia Z1 owners is provide them with Android 4.3 Jelly Bean in that same month. Google has not even officially announced what new features Android 4.4 KitKat will bring and judging by previous releases, a more likely Sony launch is into 2014