The Google Nexus 5X has been given Android 7.1 Nougat unofficially thanks to a custom ROM.
Owners of the Nexus 5X have CyanogenMod to thank for the CM14.1 ROM that brings Android Nougat to the handset. This is a nightly build and as such there may be some issues on it and some of the features don’t work as they should.
To install Android 7.1 Nougat onto your Nexus 5X you should backup the handset and make sure that you have at least 80% battery left and USB debugging is enabled. You will also need a rooted handset and have TWRP or CWM installed.
Download the CM14.1 Nougat ROM to the computer along with Google Apps and then connect the handset to the computer and transfer the files over to the SD card.
Disconnect the device from the computer after switching it off and then hold down recovery, power, volume up and volume down and you should see Bootloader or Fastboot. Use your volume keys for navigating and power button to choose. Pick Bootloader and then recovery.
Choose backup and make a Nandroid backup and you can then go to the main menu. Wipe data by choosing wipe data/factory reset and then wipe cache partition and delvik cache.
You can now install the ROM by finding it on your SDcard and choosing confirm. You can repeat this for GApps and then reboot the Google Nexus 5X and enjoy Nougat.