Folks, great news today. After releasing an open beta of Android 10 on May 1st OnePlus released Android Q stable update for the OnePlus 5 and OnePlus 5T today. This is a stable version; therefore, it is meant for everybody and should not contain any major bugs or issues. Should you however encounter any, you can report them to OnePlus on their feedback forum or from the Community app on your phone so that they get fixed in future releases.
This is also the last major Android upgrade these devices will officially receive.

We've added links for both devices (5 AND 5T).

Read below to see what's new, and more detailed instructions on how to install it.

What's new?

The official changelog is as follows: 

A few other features have also been added: smart display in ambient display, new notifications modes and Share Wi-Fi.

How do I get it?

For users running the Android 10 open beta version of OxygenOS

We linked stable build to Android Q Open Beta update method, as stable build can be installed over open beta. When next stable update will be released, we will discontinue this update method so that people using it migrates to Full Update/Incremental Update update methods.


For users running the regular / stable version of OxygenOS

You don't need to do anything as long as your selected update method is Full or Incremental update.

Should you still be running an old OxygenOS version before 5.1.4 (released in July 2018), you will need to update to 5.1.4 using the Full update method first, as OnePlus introduced partial Project Treble support with this update. After that, you will need to update to OxygenOS Pie (OxygenOS 9) by using Full update method again, as otherwise /vendor partition will not be updated correctly (I've personally noticed that camera doesn't work at all if going from any OOS Oreo build to Q directly).

For users still running the last Pie Open Beta (35 for OP5 and 33 for OP5T) released in June 2019:

You can still install this stable version by switching the update method to Android Q Open Beta update method. This can be done by tapping the three dots in the top right of Oxygen Updater, choosing Settings and selecting a new update method on that screen.

Do however consider that due to under the hood differences, a data wipe will be mandatory otherwise your device will bootloop.

Follow the instructions below:

Power off the device -> Press power and volume up key simultaneously until the device enters the Fastboot Mode

Navigate to the Recovery option using volume and power button -> Choose English -> Install from Internal storage -> Select the downloaded zip file -> Select 'Yes'

Wait until the installation is complete -> Reboot

Any recommendations?

Yes.
As general advice, backup your data before updating as it's good practice.

Rooted users: disable any Magisk modules you might have installed as they might not be compatible with Android Q and therefore lead to a bootloop.
Remember that you need to use at least Magisk 20.0 which has full Android 10 support.
As a reminder, you can download Magisk from its official GitHub repository.