Sony released a concept build of software based on Android 6.0 Marshmallow to users in Europe a couple of months ago. The purpose of doing this is that those users could test it and report back to the company in order to fix some errors or bugs before the final build is released for a number of their smartphones. The software was released as a pretty bare-bones version of what they usually offer, basically looking like the stock version of Android. Sony has been adding new features to that software to make it better and more usable. The software was supposed to be tested until mid-December, but Sony extended the testing period until early 2016. While Android 6.0 was expected to make its way through certain devices in January, this fact made us wonder if it could be delayed a little longer.
It has been reported that the Wi-Fi Alliance certified Android 6.0 for a number of the Japanese variants of certain Xperia models. The software was certified for some carrier-branded versions of the Xperia Z5, including NTT docomo (SO-01H), SoftBank (501SO) and au (SOV32), and the software for the Xperia Z5 Premium got certified for the carrier NTT docomo (SO-03H). This version of the operating system was also certified for some versions of the Xperia Z4 (this phone became known as Xperia Z3+ internationally) including NTT docomo (SO-03G), SoftBank (402SO) and au (SOV31).
The fact that the software has been certified for so many variants surely suggests that devices in that region could be updated soon. However, since the Wi-Fi Alliance is not the same as the PTCRB, which certifies cellular operator-related software in North America, the update could take quite some time before it reaches devices in that region. It has been suggested that the Xperia Z5 lineup could be updated in January and older models could follow shortly, which might be true, but the company hasn't confirmed a specific time-frame for the update to start rolling out in any region. Sony has been one of the last manufacturers to update their devices, and they usually update their latest generation devices first, the previous generation second, the generation before that third, and so on. But once the update is available for the latest generation, it doesn't take too long before it shows on older devices.