According to several developers, both in the UK and US, Apple has begun sending out iOS 9 update alerts two days before those registered in the developer program can actually get it; the Gold Master (or final version) of iOS 9 will be made available on Wednesday, September 9 to developers.
One developer received the following message: "A new iOS update is now available. Please update from the iOS 9 beta” on his iPhone 6 Plus, as shown below.
However, after seeing the message like the one above, and checking for an update, there isn"t one. It"s likely to be an error on Apple"s part, as the most recent iOS 9 version released to testers is beta 5, released over a month ago.
Apple"s iPhone event is only two days away, when we will learn more about iOS 9 and the iPhone 6s and 6s Plus which are rumored to include a better camera, 4K video recording and a "3D Touch Display".
The iOS 9 public release will follow around two weeks after the September 9 event.
Source and second image: Product Review