Just when the Google Pixel 3 roll out it latest June security patch, the OnePlus 7 which went on sale recently in the UK, Europe, India, and China is already receiving its first update - OxygenOS 9.5.4.
The update is not much different from what the phone already has, as just new few features where added and weighs 223MB in size and bumps up with additional Android security patch level from March 1, 2019 to April 1, 2019.
In addition to that, the update also brings in DC Dimming so that the phone's screen doesn't flicker at low brightness settings.
Additionally you get the Fnatic Mode as well as some optimizations for the fingerprint unlock and the photo quality. And then there are also general bug fixes and an improvement to the "smooth-scrolling experience."
The OTA should reach all the units within a week or two, and if you don't get an update notification even then, you can try pulling it manually by heading over to your phone's Settings> System > System updates menu.