It looks like Sony is rolling out its Marshmallow update to select versions of the Xperia Z2, Xperia Z3, and Xperia Z3 Compact. Specifically, it appears that the update is arriving for the D6503 version of the Z2, the D6603 Z3, and the D5803 Z3 Compact.
As noted by Xperia Blog, in addition to general Marshmallow improvements like Doze, this update brings a new Camera interface to these Xperia phones. It also adds the February Android security patch to the devices.
The models in question were previously involved with Sony's Marshmallow beta program.