Today OnePlus has started rolling out the newest OxygenOS build for the 6T. This is OxygenOS 9.0.6, and it brings with it a bunch of improvements. Chief among those is the supposedly better unlocking experience, alongside the optimized camera image processing.
OnePlus 6T gets OxygenOS 9.0.6 update with improved unlocking experience and image processing - GSMArena news
OnePlus 6T gets OxygenOS 9.0.6 update with improved unlocking experience and image processing - GSMArena news

You also get further optimized standby power consumption, as well as general (and unnamed) bug fixes and improvements. Issues with adding APNs on Verizon have been fixed, and apparently some units weren't getting notifications from the Play Store - that's also fixed now.
As usual, the new software is enjoying a staged rollout. This means that the over-the-air update will reach a limited number of users today and will have a broader release in a few days after the company makes sure that there are no critical bugs hiding inside it.
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