Nexus 6 is quite an old phone manufactured by Motorola and directly under Google’s software support. However, Nexus 6 is past the support period now. Hence, it will never receive official Android version upgrades. Google recently released official update of Android 8.0.0 Oreo. But Nexus 6 will never receive it. It will continue to receive monthly Security Patch updates. There is still a way to update your Nexus 6 to Android 8.0.0 Oreo via custom ROMS like Lineage OS 15 and AOSP ROM port.
Developers called S.i.X have deployed a near stable AOSP ROM based on Oreo. It can be rooted with either SuperSU or Magisk. It also comes with Oreo six Boot animation and all the Pixel Oreo features like Pixel stock navigation bar icons, system colors, Pixel stock sounds, AOSP Messaging, AOSP Camera, and much more. The ROM is based on Revision 8.0.0 r4 (OPR6.170623).
Currently, the LineageOS 15 for nexus 6 isn’t available. The device will sure receive the official LOS 15 build. But right now, you will have to settle for AOSP 8.0.0 Oreo ROM only.
Features of Android 8.0 Oreo ROM for Nexus 6:
Revision 8.0.0 r4 (OPR6.170623)
ROM Logo in About Phone
SuperSU or Magisk
No Forced Encryption ( Kernel )
Disable Tether checks
Oreo six bootanimation
Pixel stock navigation bar icons
Pixel system colors
Pixel stock sounds
Show link to Google Play
Allow sorting applications by size
Improve app info screen
Correctly align cursor
Quick settings pull down with one finger
Double tap to sleep on lockscreen
Remove unused drawables
Disable automatic update
Remove unnecessary videos
Option to use volume keys to control media volume anytime
Allow to swap volume buttons rotation based
Navbar double tap to sleep
Advanced Power Menu
NightLight lower temperatures
Enable SysUI tuner by default
Disable qs footer warnings
Toggle to change USB MTP/STORAGE default
Toast icon switch
Battery light customization
Launch music player on headset/bt connect
Doubletap or longpress power to toggle flashlight
Allow to customize max SMS per minute limit
Disable Lockscreen Media Art
Volume rocker music control
PhoneInfo in About Phone > status
Additional Battery saver steps
Set custom brightness for ambient display and liftToWwake
Night Light brightness mode options
Increase QS columns to 4
Add/remove QS with one click
Auto hiding IME cursors as left/right nav buttons
Display bluetooth battery status when available
Build prop tweaks
Tons of fixes
How to update Nexus 6 to Android 8.0.0 Oreo via AOSP 8.0.0_R4 ROM port?
Step 1: Make sure your device has an unlocked bootloader and rooted with latest TWRP.
Step 2: Download the latest AOSP Oreo ROM for Nexus 6 from here.
Step 3: Download the Gapps for Android oreo.
Step 4: Transfer all the files to device storage.
Step 5: Reboot into TWRP recovery.
Step 6: Wipe the current system and data.
Step 7: Flash the Oreo ROM.
Step 8: Install Busybox
Step 9: Flash Magisk for Root.
For a full tutorial, visit this page.
See: How to root Android 8.0 Oreo?