OxygenOS 9.0.5 and OxygenOS 9.0.13 over the air update are rolling out now. OnePlus 6/6T users may need to wait a few hours or sometimes even a few days to get the update notification on the phone. Alternatively, install the update manually. Below is the direct link to download the firmware. OxygenOS 9.0.6/9.0.14 changelogs:

Updated Android Security Patch to May 2019 Support for Quick Pairing of Bullets Wireless 2 added Improved stability and compatibility of Bluetooth Improved confirm password UI for hidden space Optimized photo quality from the front camera (OnePlus 6T? Fixed issue with ringtone for SMS Fixed issue with speed dial getting cleared Fixed issue loading credentials required WiFi requiring Login General bug fixes and improvements

As said above, this is a minor update with March patch, general bug fixes, and optimizations. After installing the update, users should see a new feedback tool on their phone. This new tool lets users reporting bugs and submitting feature requests. A few days back OnePlus 6 and OnePlus 6T received April 2019 security patches with OxygenOS Open Beta 16 and Open Beta 8. It brought Parking location feature, quick reply in the notification bar and a few other features to both phones. In addition, OnePlus released first public beta of Android 9 Pie for OnePlus 3 and 3T.

Download Oxygen OS update for OnePlus 6/6T

In case you want to install the update manually, then download the full firmware from below link. You can also use a VPN app to download the OTA by setting the location to Germany or Canada. Full OTA update Oxygen OS 9.0.6 for OnePlus 6 [download] – [MD5: 8420f41ac48fd82cfdeb3e3aea77a2f7] Oxygen OS 9.0.14 for OnePlus 6T [download] – [MD5: b53aeec1b3dfa4c598ee5d367e8ddd41] Oxygen OS 9.0.5 for OnePlus 6 [coming] Oxygen OS 9.0.13 for OnePlus 6T [here] Incremental OTA Oxygen OS 9.0.5 – 9.0.6 for OnePlus 6 [here] Oxygen OS 9.0.13 – 9.0.14 for OnePlus 6T [coming]

Installation

After downloading the firmware zip file, users may follow this installation guide to update the phone to latest OxygenOS version manually. (source)