There are several Nexus devices that just don’t support Android 6.0 Marshmallow, and that fact has left some owners of ancient technology very unhappy. But this is Android, of course, and there’s nothing keeping developers from tinkering with Google’s open source OS. Specifically, owners of the 2012 Nexus 7 should rejoice in this case: It’s definitely at your own risk, but you can now install an early and hacky unofficial build of Google’s latest version of Android on your phone. Here’s how to do it…
The unofficial image comes by way of a developer named Dmitry Grinberg, and his instructions on making the image yourself using the AOSP (Android Open Source Project) are published on his website. That’s the theoretically safer method of installing Marshmallow on your Nexus 4, as we can’t prove that Grinberg didn’t tinker with the full working image he provided. The good news is that if you trust him, you can download the full working image that he provided — and installing it is pretty simple.
You can download the image from Dmitry’s website (the download might take a while at the moment as he doesn’t have the most powerful servers). He suggests that you use the latest publicly available bootloader when flashing.
While we don’t have a dinosaur Nexus 7 (2012) to test it on, we have confidence that it will work given the many reports from Redditors who have praised his Nexus 4 ROM. To install the factory image, simply follow our guide. That guide assumes you already have the ADB tools installed on your computer. If you need the ADB tools, head over and download the Android SDK. The rest of the guide should be pretty straightforward (once you manage to download the image, or create it yourself, of course).