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:

The new specifications will use RCS Universal Profile 3.0, a cross-platform encryption protocol that will make it easier for iPhones and Android devices to identify each other. The profile allows for richer deep linking,

When RCS messaging became available on the iPhone with the rollout of iOS 18, the technical director of the GSM Association teased that the next major milestone for the messaging standard is the addition of interoperable end-to-end encryption.