Well, one "surprise" is that a new thing called "module stability" was invented. The Swift ABI isn't going to be the ABI-thing you are used to from C (or COM) or JVM or, well ABIs ;-) And sure, they'll give you an ABI. But whether that is going to be a _stable_ ABI is to be seen. I have some doubts given the complexity of the language, but we'll see how it turns out.