The latest update has a size of 376MB with version number MIUI 184.108.40.206.MALMIEK and also brings the April 2017 security patch update to the two smartphones. However, it is important to note that this is a Nightly built version, which means everyone is not going to receive this update right now. It is available to random users to provide feedback about the latest security patch. If the feedback is mostly positive, then the company would plan to launch the update for all the users of the above-mentioned devices.
Talking about the update, it brings a host of new improvements and bug fixes. It brings better readability along with new gallery app, Mi Video app, Mi Drop app, Mi Mover app, improved notification bar and new app vault features. Additional features include a more simplified UI and a reading mode that can turn off/on automatically at sunset and sunrise. The new update also enables users to select multiple apps and put them in a folder together and also add new widgets in an empty space with a single tap only.
Xiaomi officially revealed the MIUI 9.0 update last year in July. It was later rolled out from November 2017 onwards alongside the launch of Redmi Y1 and Y1 Lite series of smartphones. The company has previously rolled out the MIUI 9.0 update Redmi Note 4, Mi Max 2, Redmi 4 and the Redmi 4A.
As previously mentioned, the new update is available only to random users of Redmi 3S and 3S Prime users. In case you want to check the availability of the new update, you may dive into Settings >About Phone> System Updates. The device would start to look for new updates automatically.