Google has recently released Android 6.0 Marshmallow as an over the air upgrade for Nexus devices and as full ROM downloads. Unfortunately, not all Nexus devices received the update - those devices released in 2012 have failed to make the list, which means owners of the original Nexus 7, the Nexus 4 and the Nexus 10 will be stuck on Android 5.1.1 Lollipop until either Google decide to push Android 6.0 Marshmallow to the device, or it is made available via an unofficial means. Of these devices, to some minds it may seem a little unusual for Google not to release Android 6.0 for the 2012 Nexus 4 as, on paper at least, it has a similar specification to the 2013 Nexus 7. Both the Nexus 4 and Nexus 7 have what Google calls the Qualcomm Snapdragon S4 Pro chipset with 2 GB of RAM. However, under the skin the 2013 Nexus 7 uses the Qualcomm Snapdragon 600 chipset that has been "badge engineered" to appear to be the same as the S4 Pro.
Nevertheless, whilst we wait for Google to update the Nexus 4, 10 and original generation 7 to 6.0 Marshmallow (and to be clear, the signs are that these Nexus devices will not be updated), there is always the unofficial route. By unofficial, we mean that a ROM developer has pulled apart the AOSP (Android Open Source Project) code for 6.0 Marshmallow and modified it enough to run on the target device. In today's news, we've learnt that ROM developer Dmitry Grinberg has built an Android 6.0 Marshmallow ROM and it's available to download from his website, which is the source for this article showing below. Dmitry has included full instructions on how to download Android 6.0 for the Nexus 4, too.
It appears that the Nexus 4 is still a perfectly capable piece of hardware as the specifications are not too dissimilar to the Nexus 7 and it should be capable of running Android 6.0 Marshmallow, but Google must draw the line under offering support at some point. For readers contemplating installing Android 6.0 onto the Nexus 4, there are a few things to be aware of. One is that Dmitry does not provide the Google application suite so you'll need to find and flash these to the device. The other is that you would be installing an unofficial ROM onto an older device, which could cause undesirable effects. Early reports from Reddit users point to some instability running the 6.0 Marshmallow ROM such as when browsing the web or accessing the GPS. It's possible that the ROM will be improved over time, but the device might not be readily usable as a daily driver. And if something were to go wrong during the installation process, you could brick your device and turn it into a paperweight - so this is very much your own risk. However, that the update runs on a three year old device shows how well Google have optimized the code (and of course, how respectable the Nexus 4 is).