Earlier this year, Sony launched the Xperia Beta program intended to test Android Marshmallow, stating that it would run until ‘at least the middle of 2016.’
In accordance with that announcement, Sony has confirmed that the Beta program has ended, with 23.5.A.1.238 being the last build released. Do note that the Concept ROM program is not the one being discontinued in this case.
The commercial firmware update is expected to release in the coming weeks for Xperia Z2 and Z3 owners, with beta users being automatically updated to it when it hits. (Source: xda-developers)