HMD Global has already confirmed that the Nokia 6 (and all other Nokia Android phones) will be updated to Oreo, but there's no timing available for each update's release. If you've got a Nokia 6 and don't feel like waiting for your Oreo treat any longer, you can now try a pre-release version.
HMD is now offering an Android Oreo beta for the Nokia 6. Simply register with your email, Facebook, or Google account and then validate your phone using its IMEI and carrier. The update should then be pushed to your phone over the air.
The update brings Oreo features like picture-in-picture and notification dots as well as the December 2017 Android security patches. You'll need to connect to Wi-Fi to download the 1140.4MB update.
As with other beta updates, this version of Oreo for the Nokia 6 may have some bugs, so be aware of that before putting it on your phone. In exchange for living with some bugginess, though, you'll get to try Oreo on your Nokia 6 before most other people.