The GSMA published a blog post to announce the new features coming to RCS. The iPhone is getting end-to-end encryption RCS messages via the Messaging Layer Security (MLS) protocol:

Apple will, at long last, enabling end-to-end encryption for RCS messages, allowing iPhones and Android phones to text each other with the security encryption provides for the first time.

Today, the GSMA made it official in the RCS Universal Profile 3.0, and, true to its word, Apple is already preparing to adopt the new profile, bringing full E2EE to RCS conversations between iPhone and Android users.