While Nexus owners have been working with Android 6.0 Marshmallow for the better part of a month at the least, devices from manufacturers like Sony and others are still being tested with the software so that it might soon be sent out to those who own the phones. Some Xperia users are already running an early stage build of the Marshmallow software as part of Sony's concept builds, which they announced back in October and started pushing out to about 10,000 beta testers. Towards the end of October they began pushing out more builds to testers, and now they have announced that they will be extending the initial time frame of the concept testing into the new year.
The trial was only supposed to be in place for a couple of months and was going to end sometime this week, but with this news it's clear that Sony likely feels they have more work to do with the software, or perhaps they just want people to have more time with the software before they take end things. Either way, this extension should allow Sony to fine tune every angle and every detail of the new software before eventually rolling it out to device owners as a stable and final build.
Sony's announcement most certainly comes as a surprise, and a good one at that, to the testers of the Marshmallow concept as it means they get to spend more time experiencing the software and all it has to offer, which compared to Sony's Lollipop software, comes with an even more stock Android feel to it alongside the usual Sony touches. This could mean that Sony will end up pushing back the release dates for the final software to the public, and Sony have noted that they haven't decided how long this extension on the concept test will run, just that it will be continuing until sometime in 2016 after the first of the year. Sony has at this point in time not announced any release windows for the official software updates, but for those on Xperia devices hopefully it won't be too far off.