heroku run is now available for Fir-generation apps

Change effective on 08 September 2025

You can now run interactive one-off dynos with the heroku run CLI command in Fir. The default one-off dyno size for apps using Fir dynos is dyno-1c-0.5gb. Ensure that you have a SSH key before using the feature.

Unlike one-off dynos for Cedar-generation apps, you must connect to a Fir one-off dyno within 120 seconds. Additionally, the inactivity timeout limit for Fir is 15 minutes, instead of 1 hour like most Cedar one-off dynos.

See One-Off Dynos, Working with One-Off Dynos, and our blog post for more info on one-off dynos and the heroku run commands.