Vivo S1 started receiving Funtouch OS 11 based on Android 11 update. Vivo S1 was announced on July 2019 based on Funtouch OS 9 based on Android 9.0. And last year it received Funtouch OS 10 based on Android 10. And Now its getting its 2nd Major Android 11 update and Probably the last major update based on Vivo Update track record. Although Vivo Have Now improved its update schedule much better than prior years.
It currently rolling out for limited users. The Update size is around 3.27 GB with Build Number EX_A_8.71.10. It features number of changes and also improves system stability. The Security Patch also jumps to March Security patch. To check out FunTouch OS 11 Features check out Here.
As of Now (22 April) Known issues include some stutters here and there, Auto Rotate Not working properly and for some users Amazon Prime Not working. Hopefully this should be fixed soon as this is a limited roll out.
As usual the update is rolling out to a small number of users. And should be getting wider roll out in coming weeks. As usual always Backup important files before updates for your safety.
To check update manually goto Settings > System Update > Check.