The Sony Concept team announced that it's preparing an Android 7.1.2 concept update for the Xperia X smartphone. Concept releases
are a way to get the latest pure Android version running on your Xperia phone
if you would like that in place of the official Sony firmware, which is a reasonably clean build of Android as well.
The Android 7.1.2 update will bring Bluetooth connectivity improvements, battery usage alerts, and various other fixes. Notably, this Android build gave Google Pixel and some Nexus phones issues with their fingerprint sensors. The changes Google applied to this part won't be included in the Xperia X Concept Update.
A drawback to the update is that the setup wizard for the initial setup (or after performing 'factory reset' and 'add user' functions) after powering the phone will only work with Wi-Fi. It's not very likely you will be impacted by this in any major way.
The concept update is ready for release and is going to be published soon. The Xperia X Concept program is only available to Sony's European users for some reason. You can read more about the Xperia X here