The official rollout of Android 10 has already started for the OnePlus 7 and 7 Pro, but older OnePlus devices are still without the latest software. That won't be the case for too much longer, though, at least for some phones. OnePlus has shared a tentative schedule of when the OnePlus 6T, 6, 5T, and 5 will see the update, and it's as soon as this month.
The OnePlus 6T and 6 are scheduled to get an Oxygen OS Open Beta based on Android 10 sometime in the next couple of weeks, before the end of October. A stable build is expected to follow in November. The 5T and 5 won't be getting Android 10 Open Betas at all, but a stable update is planned for the second quarter of 2020 — that's sometime between April and the end of June.
In a forum post, OnePlus notes that "software development requires rigorous development and meticulous testings," and reiterates that the above dates are approximations that assume there aren't any hiccups in development. Considering how quickly the 7 Pro moved from Open Beta to stable, though, it seems likely the 6 and 5 families will stay on track.
- OnePlus Community forum