Bigger Slugs and Greater Build Timeout Flexibility

Modern applications, especially those leveraging AI and data-heavy libraries, need more room to breathe. To support these evolving stacks and reduce developer friction, we’ve increased the default maximum compressed slug size from 500MB to 1GB.

Understanding app slugs and deployment

App slugs are the container build artifacts produced by Heroku Buildpacks and run in dynos. Allowing larger slugs makes it easier to deploy apps with large library or package dependencies on Heroku. Many AI and machine learning libraries fit this pattern and we’re looking forward to seeing what new types of apps will be possible with the higher limit.

How this can affect your dyno boot times

While the new 1GB limit provides more headroom, there is a direct correlation between slug size and dyno boot times. Larger slugs are slower to download and extract and starting large apps takes longer, which can slow down common tasks like scaling and heroku run commands. We still recommend that you try to keep slugs small and nimble to ensure optimal performance.

Increased build compile timeouts for complex apps

We’re also increasing the build compile timeouts as part of this change. Build timeout is another limitation commonly hit for complex Heroku apps with many dependencies. Heroku already has a lot of flexibility to allow occasional long-running builds when build caches are cleared, and today’s update increases these timeout limits across the board.

Removing deployment friction for developers

Slug size limits and build timeouts weren’t just minor inconveniences, they were recurring points of friction that disrupted developer flow. By easing these constraints, we’re ensuring that your deployment pipeline stays out of your way, allowing you to focus on building complex applications.