Seems like Sony will be the first this time (Obviously after Google and Motorola) to bring Marshmallow update for its flagship lineup. Today Sony started rolling out Marshmallow based Beta firmware called “Concept for Android” for Xperia Z3 and Xperia Z3 Compact. Sony will keep improving the firmware based on user’s experience and feedback. They will gradually roll out new updates over coming weeks.
Using this Concept for Android App you can register for the Marshmallow concept update and taste the new firmware before others. Just note, you must be Xperia Z3 or Z3 Compact user based in Sweden, Denmark, Norway, Finland, Iceland, Estonia, Latvia, Lithuania, United Kingdom, Ireland or Germany. So go ahead and download the right away. You can even download its APK file directly from this page.
Download APK | Download from PlayStore