Sony recently started to roll out the KitKat Update for the Xperia Z1 globally in all the markets. The software update marks as 14.3.A.0.681 and apart from bringing in the latest version of the Android OS, it also brings in some features.
It brings in the new and the updated camera interface which is said to be improving the overall shooting experience with your Xperia Z1. Also the camera software is improved so it would let you capture brighter photos as compared to before. Also Sony has update the email app, but we dont know exactly about the interface changes that Sony has brought in thr email app.
Also apart from new features the update also brings in some bug fixes and improved performance of battery. So if you have not got the notification about the update, maybe you should be checking manually about it, by navigating into Settings > About phone > Software updates. Update your device, and let us know how it feels in the comments below.