https://techcrunch.com/2017/08/21/apple-just-shared-ios-11-beta-7-to-developers/

Apple just dropped a brand new beta for iOS 11. And you know that iOS 11 is going to be your favorite major iOS update of the year, as there’s only one per year. The company has been testing iOS 11 for a couple of months already. Don’t forget that the beta program is primarily targeted at developers working on app updates.

I still wouldn’t recommend installing iOS 11 on the iPhone you use every day. The changes in iOS 11 will take some time to pay off for your iPhone anyway. And beta versions of iOS usually drain your battery life.