Is iOS 7 paid and does it also work for iPhone 4S?

Apple is launching out new iOS this 7 on the same month it use to release iPhones every year. So they seem to show a lot of improvement in the software and no new device is coming out so is it required to pay for iOS 7

IOS 7 is an update, it'll be free.
There have been rumors that a new iPhone will be released, however, it was not mentioned in WWDC.