Change effective on 24 January 2017
Heroku Autoscaling lets your app automatically adjust its quantity of web dynos to maintain your specified response time as the amount of incoming traffic changes. Autoscaling never adds web dynos beyond a limit you specify, which means you never incur unexpected costs.
Heroku Autoscaling is available for Performance-tier dynos and dynos running in Private Spaces. See the Dev Center for more information.