As the world turns, so too does the cycle of Android updates. The first part of 2017's version bump, known only as Android O for the time being, was just announced. And just like the last two years, developer preview versions will be available for some of the latest officially supported Google hardware. This year that list includes the Nexus 5X, Nexus 6P, Pixel, and Pixel XL phones, the Pixel C tablet, and the Nexus Player Android TV set-top box. You can download the new images here.
The Nexus Player is the big outlier here, since it's coming up on three years old. But despite being officially discontinued (and one of only a handful of standalone devices that actually use the platform), it's still the only retail Android TV hardware Google has ever produced. The Nexus 5X/6P generation and the Pixel C are both from late 2015. The Nexus 6 phone and Nexus 9 tablet, both still supported as of Android Nougat, are not part of the program.
Note that these releases are the first Developer Preview, not part of the wider Android Beta program, so current devices can't be upgraded with an over-the-air download. You'll need to download the images and flash them manually with Fastboot on a local PC. This initial developer preview is not intended for daily use - though a lot of enthusiasts are going to update their phones anyway - so prepare for a few bugs and incompatible apps as Google and app developers work through the teething troubles.
- Android Developers