As of May 1st, 2023, Heroku will no longer be supporting the Heroku-18 stack. The reason for this deprecation is to maintain synchronization with the Ubuntu Long Term Support releases. If you are currently running your Rails application on this stack, when you navigate to the Heroku dashboard you will notice a warning to upgrade to either Heroku-20 or Heroku-22 before the end of the Heroku-18 stack life on April 30th, 2023.
While Heroku-18 will not be supported, do not be alarmed or concerned that the apps running on this stack will stop working. Heroku has confirmed that all existing applications will not be interrupted and non-build functionality will still be available. However, to maintain access to security updates, technical support and the ability to perform new builds, an upgrade will be necessary and is highly recommended.Read more