A Formal Analysis of Apple’s #iMessage PQ3 Protocol:
"Moreover, #PQ3's integration of hybrid-cryptography into the double ratchet provides stronger guarantees than #Signal, where a post-quantum Key Encapsulation Mechanism (KEM) is just integrated into the protocol's setup phase, but not into its ratcheting".
https://www.usenix.org/system/files/conference/usenixsecurity25/sec25cycle1-prepub-595-linker.pdf