"Swift and Objective-C Interoperability" - WWDC 2015 (Nullability qualifiers, audited regions, generics, typed collections, kind of types)
https://developer.apple.com/videos/play/wwdc2015/401/
"What's New in LLVM" - WWDC 2017 (API Availability checks, ARC warnings and stronger function declarations)
https://developer.apple.com/videos/play/wwdc2017/411/
"What's New in LLVM" - WWDC 2018 (ARC updates)
https://developer.apple.com/videos/play/wwdc2018/409/
"What's New in Clang and LLVM" - WWDC 2019 (runtime optimizations)
https://developer.apple.com/videos/play/wwdc2019/409/
"Advancements in the Objective-C runtime" - WWDC 2020
https://developer.apple.com/videos/play/wwdc2020/10163/
I didn't fell to go all the way back to the WWDC 2006 when Objective-C 2.0 was announced.
Explicit enough?