OnePlus today announced OxygenOS 9.0.16 for the OnePlus 6T and OxygenOS 9.0.8 for the OnePlus 6. These updates include the August 2019 Android security patches, Quick Reply in landscape mode, a new Fnatic gaming mode, more Zen Mode features, and more.
Here's the official changelog for these updates from OnePlus:
This update is now rolling out over the air, but as with most OnePlus updates, it's only going out to a small number of OnePlus 6 and 6T customers to start. After OnePlus has confirmed that everything is working smoothly, it'll begin a broader rollout.