Android Developer Previews have been for Nexus devices only—Google develops Android, so it makes sense that its devices run the developer builds. Sony apparently feels left out, though, and has provided binaries and instructions for taking the new Android Open Source Project (AOSP) Android M Developer Preview code and turning it into something that will run on certain Xperia devices. Through Sony's "Open Device" program, the Xperia Z3, Z3 Compact, Z2, Z2 Tablet, Z1, Z1 Compact, E3, M2, T2 Ultra, and T3 are all supported.
Google launched the Android M Developer Preview late last month and has promised several updates between now and the eventual consumer launch. Android M adds user-selectable permissions controls, a fingerprint API, better standby battery usage, and a ton of tweaks. There are even a few experimental features like a multiwindow mode, and Google plans to use the new Assistant API to build a contextual layer called "Google Now on Tap" into the entire OS.
While many users end up running the Android Developer Previews for fun, Sony's implementation sounds like it's for advanced users only. The instructions involve downloading AOSP to your computer, downloading additional files from Sony's repo, downloading the proprietary binary files from Sony, and then compiling everything into a build for your Xperia device. The lives of Nexus users are a lot easier—Google posts ready-to-flash packages on the Nexus System Image page.
Sony posted a video of the build in action, and judging from the video, the build appears to be straight from AOSP—not the Nexus-style loadout that you might expect. There are no Google Play apps, and the device is full of abandoned AOSP apps like the Gallery, Browser, and Messaging. Still, the point is to test Android M, and if you don't have a Nexus device handy but do have an Xperia, you have a solution now.
The Android ecosystem would be a wonderful place if every OEM were this cooperative. Sony runs a GitHub page with prebuilt kernels and all the necessary config files to make AOSP work on your device. It contributes big features to AOSP like its "RRO" theme engine. And now it's supporting developer previews on its devices.
Now we'd like to see Sony take advantage of this AOSP work and turn it into fast updates for its users.