Sony changed their strategy of their flagship smartphones when they introduced the Xperia Z lineup back in January 2013. They introduced their OmniBalance design with the new hardware which has been present, for better or for worse, even in their most recent Xperia Z5 lineup with few changes (or let's say, refinements) from the older generation to the newer one. Also, some models were waterproof, which has been a highlighted feature that's also been present on many models including the recently announced ones. The flagship models would also be updated in a 6-month release cycle to keep them competing with the newly announced hardware in that time frame.
The company surprised everyone when they claimed that all of the Xperia Z models would be updated to Android Lollipop, as some smartphones released by the same time would not get the update. That promise has been kept with the newer models getting the update first and the older ones getting it a little later. Now, it has been reported that some older models of the Xperia Z lineup are getting Android 5.1.1, which is the most recent release. The firmware has the number 10.7.A.0.222 and the models that will receive it are the original Xperia Z (models C6602 and C6603), Xperia ZL (models C6503 and C6506), Xperia ZR (C6503). As for the tablets, the Xperia Z Tablet in the Wi-Fi variants SGP311 and SGP312 and the LTE model SGP321 will get the update shortly.
This has kept the owners of the Xperia Z1 and Xperia Z1 Compact wondering when are they getting the update, as this newer version is supposed to fix a lot of bugs and issues that the version of Android 5.0 had. While there are no reports on when this might happen, reports are coming in that it is landed on some devices. It is worth remembering though, that the update process can take some time, as companies have to optimize the firmware for each smartphone and it's better if they do take the time as this can help to prevent issues from occurring. Although, moving forward, it will be interesting to see how many devices from the company are updated to the newer version, Android Marshmallow when it is released.