It's still in Beta testing so I think it will be released sometime in the Fall. More info about it here.
iOS 10 release date, new features & supported iPhones & iPads ...
When is ios 10 coming out for the public?
iPhone 7 event is supposed to be September 7th, and phones (along with the new OS) are always released a few weeks after that, so it will probably be released the end of September?