Update: After pulling the RUU file for the HTC 10 Oreo in the U.S. the company has started rolling out the update in Taiwan (v3.16.709.3) and Hong Kong (v3.16.708.3), other countries should get it soon.
Earlier: HTC confirmed Android 8.0 (Oreo) update for some of its devices back in August last year. The HTC U11 was the first phone to get the Oreo update in November starting from Taiwan, later the U11 Life got the update, now the unlocked HTC 10 units have started receiving the update starting from the U.S.
Android Oreo comes with lots of new features and improvements including Background limits, Notification channels, snooze notifications, Autofill APIs, Picture in Picture (PIP) display, Adaptive icons and much more.
The v3.16.617.2 for the HTC 10 also includes Android security patch for December, 2017. OTA update should roll out for unlocked units in the U.S. from today, but the RUU file is available, which you can download and manually flash at your own risk.
No details when the T-Mobile and other carriers variants will get the update. European units should get the update later this month or early next month. HTC U Ultra is expected to get the Oreo update next as the company had already promised."HTC 10 Android 8.0 Oreo update starts rolling out",