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Automatic app archiving
Change effective on 26 August 2013
Heroku will now automatically archive apps older than 3 months that have never had a user-initiated deploy. That means only empty apps, or apps created from templates and never changed, will be archived. An archived app will not be running any dynos and will yield a “No such app” response when accessed using its .herokuapp.com
domain.
Read more about app archiving on Dev Center.