While Android 6.0 Marshmallow may have been announced last September, it's only now that we are beginning to see it come to more and more smartphones and tablets that run Android. This is quite normal in the world of Android, unfortunately. Now, Sony appears to be next in line to roll out Android 6.0 Marshmallow. They are bringing it to the Xperia Z2, Xperia Z3 and Xperia Z3 Compact. However it's only coming to a few specific models. And no, there are zero carrier models included here (that includes the Xperia Z3 from T-Mobile).
The models that are getting Marshmallow as of today, are the same ones that were part of Sony's Marshmallow Beta program that the company began in February of this year. This includes the Xperia Z2 model D6503, the Xperia Z3 model D6603 and the Xperia Z3 Compact model D8503. All other models will have to wait a bit longer before they get their precious Android 6.0 Marshmallow update. It shouldn't be too much longer though, as long as there are no issues with this Marshmallow update.
This update brings these three models to Android 6.0, and also brings the February 2016 security patch. With Marshmallow, you're getting things like Doze. Which was a pretty popular and exciting feature for Android 6.0 Marshmallow, because it means much better standby time. With Doze, if you haven't used your phone for a good while, it will go into deep sleep, thus extending your standby time. It's especially noticeable on tablets, more so than on smartphones. On top of that, you're also getting Google Now on Tap, allowing you to have Google Now on any screen. If you're on a web page, just hold down the home button (on devices with software buttons) and Google Now will pull in some information from that page to show you. For instance, if you're on a page that mentions a company like Sprint or T-Mobile, it'll give you information about those companies.
The update should be available now for these three models, and if you own one of them you'll be able to download the update now. Just head into Settings, then tap on About Phone, System Updates and tap on Check for Updates and it should download momentarily.