If you own a Sony Z3 Compact, the official Sony updates are limited to Android 6.0.1 - alternative ROMs such as CarbonROM provide a remedy.
Sony itself won't provide any further updates for the Z3 and the Z3 Compact - Android 6.0.1 remains the latest version. Fortunately, Sony allows the simple unlocking of the bootloader so that other ROMs can be installed.
Before CarbonROM can be installed, a custom recovery system must be installed: TWRP is a common system for this. The latest version of CarbonROM is available on the project's website at get.carbonrom.org
After the flashing, whereby all data is lostthe new ROM is available. After the first version was still a bit "bumpy" (the camera didn't work at first go), most of the problems are solved with the current version. Advantage of the weekly updates: the security fixes are also always up to date.
CarbonROM 7.1.2 in everyday life
Even though the Z3 Compact is not one of the newest devices (it was introduced in 2014 and works with a Snapdragon-801-SoC), the everyday performance is still good (and significantly better than the Moto G 1st generation). The only disadvantage: the camera quality suffers because certain DRM codes are lost during flashing. But the camera remains quite usable. Also the hardware buttons (mainly the camera button) do not work 100%.
The other advantages of the Z3 Compact (water and dust protection, small display and good battery life) are of course retained, but with the latest Android. Used devices are available on Ebay for about 130,- Euroand in some cases even cheaper.
Update: CarbonROM 8.1
The makers of CarbonROM have discontinued the variants based on Android 7.1.2, skipped version 8.0 and jumped directly to the current version 8.1 "Oreo": CarbonROM "Noct“. If you already had CarbonROM installed in the previous version, you can update to the new version using your existing recovery system.
The changes are still very subtle, basically it corresponds to Stock-Android. What works better than in the previous version is the camera button on the Z3 Compact, which can now actually be used to release the camera and focus.
Apart from that, there are still weekly updates that can be installed as a partial update - but this still seems to be a bit shaky, at least on my device the update hung up once. Another problem is that not always the device name seems to be set correctly. This can only be solved by unpacking the ROM-ZIP and adapting the corresponding files, but after that the installation is problem-free.
The Z3 Compact from Sony thus gets another significant lifetime extension, after the Snapdragon 821 is still quite competitive (and faster than for example the Snapdragon 625 in the Xiami Mi A1).