Released in June 2017, the OnePlus 5 and 5T have already received two OS upgrades. However, the company committed to upgrading both devices to Android 10, which would be their third OS upgrade. Now, it seems that the final update for the OnePlus 5 and 5T will be arriving towards the end of Q2 2020.
https://www.notebookcheck.net/OnePlus-5-and-OnePlus-5T-to-receive-Android-10-in-Q2-2020.457455.0.html