Two obscure Swift changes I want to note:
ASCII String literals bridged to ObjC will produce a different type in the beta OSs. This generally has no impact (other than greatly improved performance), but code incorrectly treating `NSString *` as `char *` or `SEL` may need to change (e.g. %s format strings).
A message will be logged in any situation we're applying compatibility workarounds for this, and the workaround will be disabled if you use the latest SDK version.