In December, Apple announced that RCS is finally coming to iOS, but left a possible release date vague, stating support would be added "later next year." In a recent landing page for Google Messages — which has since been removed — Google revealed that "Apple has announced it will be adopting RCS in the fall of 2024," giving iPhone users a more concrete timeline to look forward to (via 9to5Google).
Most people assumed that Apple would release RCS support with iOS 18 rather than an iOS 17 update later in the year, but this 'fall of 2024' information basically confirms it'll be an iOS 18 feature. RCS support will likely be added as a feature for the first iOS 18 release, but it's possible that it could launch in October or November as an update feature and still meet the 'fall of 2024' deadline.
