Iris: fastest go web framework

It's the fastest go framework!! it says that you the server is optimizing itself at the runtime, if you use more than one core it uses other router, if you have domains in your router it uses other router mechanism if you use cache it uses other router. It is real I am using this framework 1 week for a site with million requests it operates faster than httprouter and gin and others I tried before

Do they have a document talking about what they did to achieve those speeds?

I wonder if a framework that uses fasthttp instead of net/http can be even more performant.