OnePlus has confirmed that the OnePlus 5 and 5T will receive Oreo beta updates by the end of the year, with the full, stable update to come in early 2018. The Oreo beta program for the OnePlus 3 and 3T has been opened for months.
https://www.notebookcheck.net/The-OnePlus-5-and-5T-will-receive-Oreo-by-the-end-of-the-year.264000.0.html