The OnePlus 5T has been updated to Android 8.1 Oreo, but only if you're on the Open Beta program. OnePlus has also added the ability to backup app data, in case you are looking to switch smartphones in the near future, and of course there are some changes to the system - which include being updated to the February 2018 security patch.
The latest OxygenOS beta released for OnePlus 5T contains the overlay image attached above which shows that the display will have a cutout so as to optimize the apps for this cutout.
The OxygenOS Open Beta 6 version comes with general bug fixes and performance improvements, but no other details about camera upgrade or any other performance based upgrades has been mentioned yet.
The update introduces a new feature called "Gaming Mode", which enables immersive gaming experience including power saving and pausing adaptive brightness.
For the OnePlus Switch, the company has also added support to migrate application data, allowing users to switch between devices seamlessly. However, for those who've not flashed Open Beta build, they'll need to flash this new update manually by downloading it from downloads.oneplus.net.
Users can download the open beta ROM for their OnePlus 5T by downloading it from the official website.
Do note that since these are beta builds, you may face some issues with stability. Those running the open beta on their OnePlus 5T smartphones will get this as an Over-The-Air update. OnePlusalso actively maintains a forum, where key announcements are made and feedback is taken. However, advanced users can get a taste of upcoming features and software through the open beta program, before these features are thoroughly tested and rolled out as stable OTAs. There is no word from OnePlus regarding the older phones' 3/3T 8.1 updates as they are on Android 8.0 already. This means, OnePlus 5T users will be able to answer an incoming call just by picking up the device in hand.
In addition to this, the Open Beta 4 update rolls out the gaming mode to the OnePlus 5T.