[riscy]

> One thing that isn’t part of the [RCS standard ratified by GSMA] is the encryption standard Google is adopting. It’s building it on top of RCS right into the Android Messages client.

> If you are texting with somebody who isn’t using Android Messages (say, somebody using Samsung Messages or an iPhone), the fallback to either less-encrypted RCS chat or SMS will still work just fine.

Sounds like Samsung users need to separately download Android Messages to get E2EE.

Quotes from https://www.theverge.com/2020/11/19/21574451/android-rcs-enc... which is cited by Wikpedia on RCS.