Sony Mobile and Japanese carrier SoftBank have released an Android Marshmallow update that sees the return of the STAMINA mode, as expected. The battery-saving mode was axed when Marshmallow first arrived, as Google’s native Doze feature does something very similar. The new firmware build number 32.1.D.0.284 is currently live on the Xperia Z4 (402so), which also includes STAMINA mode. The Xperia Z4 has been updated to build number 32.1.E.1.38.
Source:- Xperia Blog