Earlier, OnePlus had made a commitment to bring Pie to its older flagship series. However, the company later admitted that this upgrade would be delayed. Now, it seems that the prospect of Pie for last year's phones, the 5 and 5T, is back on the table with a new Hydrogen OS beta based on the latest version of Android.
https://www.notebookcheck.net/New-reports-suggest-promised-Pie-based-upgrade-coming-to-OnePlus-5-and-5T-soon.361466.0.html