Binaries are used by Sony, or third parties, to make sure that AOSP will run on specific pieces of hardware. This release doesn’t allow Sony handset owners to run Sony’s official Android 5.1 on their smartphones just yet, but it does show that development in under way for all of these devices.
XDA forum member cheep5k8 has already taken the files and implemented an early alpha AOSP 5.1 build for the Xperia Z2. Most of the features already work, except the camera and a few sound glitches, but you’ll need to know what you’re doing with .img files if you want to test it out. Perhaps waiting for a more polished build would be wise.
Previously, Sony’s Twitter account had responded that Android 5.0 Lollipop would only be heading to Xperia Z branded devices. Either Sony was being cheeky and knew that it would be skipping 5.0 straight to 5.1 for some of its other devices, or, more likely, there was some miscommunication between Sony engineers and its social media team.
Hopefully we will hear official news from Sony regarding Android 5.1 updates for all of these handsets in the near future.