Shortly after Google announced the new version of their mobile operating system, Android 4.4 KitKat, Sony Mobile News posted a tweet saying that details regarding Android 4.3 and Android 4.4 on Xperia devices will be made available next week. The "Sony Viet" news site has some spicy information along those lines.
According to the publication, Sony will update the Xperia Z, Xperia ZR and Xperia ZL to Android 4.3 Jelly Bean before the end of 2013 (in fact, the Xperia Z should be getting the update this month itself). After the update, all three phones will feature the same UI and updated apps as seen on the new flagship Smartphone, the Xperia Z1. Speaking of which, the Z1 and Z Ultra (phablet) will "leapfrog" Android 4.3 in favor of Android 4.4 KitKat.
In any case, don't expect the update to arrive anytime soon. The earliest that we can expect is late January or early February, 2014. Even then, the update will be arriving sooner than any other OEM updates their phone to the latest version of Android. Thankfully, there's not much to miss on Android 4.3, and users will be perfectly happy with Android 4.2.2 for two or three more months.