The latest version of Android, the Android Pie was officially introduced by Google to its device with its launch on Monday. And since then Essential was the only third-party OEM to introduce the Android 9.0 update on its device. No other companies have shared its details on the next major OS update with Android Pie, except for Vivo.
In an email emailed to Android Authority Vivo made a statement that it will be rolling out its Android 9.0 Update in the fourth quarter of this year.
Unfortunately, specific date or time is not shared, so just as a guess to be on the safer side lets say that we can expect updates to start rolling out close to December 31.
Vivo did not release the list of devices that will be blessed to get the update, but the email was sent in reference to the X21, so it may be the first one to get the 9.0 update and following up that list would be the flagship NexS or both could get the update at the same time.