Sony has started seeding Android 4.4.2 KitKat updated for the Xperia Z1! However, firmware version 14.3.A.0.681 may still not be available for your particular Z1 unit as these sort of things come in stages, with some markets getting the goodies before others.
Aside from new features and tweaks KitKat brings, Sony also updated its Camera app and overall improved the camera experience. In addition, there’s an “enhanced email app” for those who don’t use GMail, as well as the usual stability, performance and battery improvements.
If you bought the Xperia Z1 from a carrier, you’ll have to wait a little longer before they test out the new software. Hopefully, that won’t last forever, but you are always free to bug them with questions like “when will I get the update,” and “guys/gals why everyone else is getting the goodies but me.” Perhaps that helps. 😉