Google's Nexus lineup, including Nexus 5, 6, 7 (2013), Nexus 9 and Nexus Player, were the first to receive stock Android Marshmallow upgrade, whereas the newly-launched Nexus 5X and 6P shipped with the latest Android version on board. But Google stopped further Android support for the Nexus 4 and the Nexus 7 2012.
A lot of beta builds based on Android Marshmallow are already available and the first one among these was released by developer Dmitry Grinberg. This was a pre-built AOSP Marshmallow ROM. For those who were disappointed over the official CyanogenMod support, here is some good news. The CyanogenMod team has released the official CyangenMod 13 nightly build for the smartphone.
Based on Android Marshmallow, the CM13 nightly brings Marshmallow flavour for the Nexus 4.
The team has so far released a handful of nightly versions. Choose the latest one to get the most stable version incorporating all the fixes, with more improvements to come in due course. You can download the nightly directly from the CyanogenMod site and click here if you are looking for a step-by-step guide to install the CM13 build on the Nexus 4.
Download: CyanogenMod 13 nightly for Nexus 4