After a few beta testing, finally, OnePlus released OxygenOS 5.0 (Android 8.0 Oreo) for OnePlus 3 and OnePlus 3T, whereas Android 8.0 Oreo based Open Beta is also available for both devices. OnePlus starts rolling out OxygenOS 5.0 OTA (over-the-air) update for both devices and since it rolls out in phases, it will take a week or more to get on your device.
You can also download the OxygenOS 5.0 update (OTA/Full ROM) for OnePlus 3 and 3T and install manually as described below. If you prefer OTA update over manual installation, but cannot wait for the OTA, then you can use the Opera PN app and change the location to Germany or Canada to get the OTA update early.
OxygenOS 5.0 (Android 8.0 Oreo) brings a bunch of new features and latest security patches (September, 2017) alongside general bug fixes. The update brings new features like Parallel Apps, Picture in Picture, Smart text selection, Auto-fill and more to OnePlus 3 and 3T.
Highlights of OxygenOS 5.0:
Update to Android O (8.0)
Added Parallel Apps
Added Picture in Picture
Added Smart text selection
New Quick Settings design
Updated security patch to September
Added notification dots
New app folder design
Now able to upload photos directly to Shot on OnePlus
Download OxygenOS 5.0 for OnePlus 3 and 3T:
OxygenOS 5.0 Full ROM Update Method
Note: This guide requires ABD and fastboot set up on your PC. Also, both devices require unlocked bootloader. Backup data before proceeding.
1. Enable ‘USB Debugging’ on your phone in Settings > Developer Options.
2. Save the download OxygenOS 5.0 Full ROM zip file inside the ADB installation folder.
3. Switch off OnePlus 3/3T, press Power + Volume Down buttons together to boot into stock recovery.
4. In recovery, choose “Install from USB” option, tap OK to confirm. A screen with “You are in sideload mode” will be displayed.
5. Connect your OnePlus 3/3T to PC/Mac and issue the following command in command prompt /terminal
adb sideload File Name.zip
./adb sideload File Name.zip
[File Name.zip=OxygenOS 5.0 file name]
7. Wait a while, your phone should now update to the selected build and reboot automatically to take you into OxygenOS 5.0.
OxygenOS 5.0 OTA Update Method:
1. Save the downloaded OxygenOS 5.0 OTA zip file on your phone’s memory.
2. Turn off the phone and boot into recovery (Use Power + Volume Down buttons).
3. In recovery, select ‘Apply Update’ and select ‘Choose from Internal Storage‘
4. Browse the OTA zip file (you just saved) and select it. The update will start and reboot automatically after finishing the update.
(Source – OnePlus)