What shipped, newest first.

Mark a server with the builder role and it takes over compiling. Images are pushed to a shared registry, and your serving hosts only ever pull — so a heavy build never competes with live traffic on a small app server.

Builds also gained a registry-backed BuildKit layer cache shared across hosts, one build slot per machine, and a memory cap so a large compile fails cleanly rather than taking the box down.

A deploy is no longer considered finished when the container passes its readiness probe. The agent now probes the application through the proxy over HTTPS and requires five consecutive clean responses before moving traffic.

The probe no longer follows the HTTP-to-HTTPS redirect, which previously let a deploy report success against the redirect rather than the application.

A repository with a Procfile now declares its own process types and release hook. Web and worker processes start from the file, and the release: entry runs before the new version takes any traffic.

Repositories with no Dockerfile can now build with Cloud Native Buildpacks against heroku/builder:24, using prebuilt runtime layers instead of compiling a language from source. The built image is published to a registry and pulled back for the run.

This is the fastest path for an application migrating off Heroku, since it reads your repository the same way Heroku’s own build does.