How to enable production mode in RC0

Automatically enabled! how come.
But the browser still display
"Angular 2 is running in the development mode. Call enableProdMode() to enable the production mode."

I think it’s not in prod mode by default and we have to enable it in order to run the “src/app/main.prod.ts” file not “src/app/main.dev.ts file”, but I don’t know how?