If it works like in Zig (which also currently integrates Clang), then it will compile C, C++ and ObjC source files directly to LLVM IR, and headers to AST-level

If it works like in Zig (which also currently integrates Clang), then it will compile C, C++ and ObjC source files directly to LLVM IR, and headers to AST-level and then use that rich AST information to generate Swift interfaces on the fly. The main difference to Zig seems to be that Swift can also generate bindings for C++ interfaces while Zig is limited to C interfaces.