While Sony’s Xperia Z5 and Z5 Compact have just made their way to the US, their British equivalents should start getting Marshmallow early next month. According to the Xperia UK Twitter account, the Z5 series, Z4 Tablet, and Z3+ should get Android 6.0 on March 7th with more details coming later.
Sony has been testing Marshmallow through their Concept for Android program with several thousand people for a few months now. For the most part, Sony very lightly skins Android and provides a close to stock experience. Their concept launcher is similar to the Google Now Launcher and has since been ported to other devices by the developer community.
The company has already confirmed that quite a few generations, including the Z5, Z3+, Z2, and various other low-end devices and tablets, will get updated to Marshmallow. The US version of the Z5 and Z5 Compact should get their updates shortly after that. The rather expensive and fingerprint sensor-less devices have already received price cuts since their US launch a few weeks back.