Bundler version 4.0.0.beta2 is now available for Ruby Applications
Change effective on 02 December 2025
The Ruby Buildpack installs a version of bundler based on the major and minor version listed in the Gemfile.lock under the BUNDLED WITH key:
BUNDLED WITH4.0.x will receive bundler4.0.0.beta2
It is strongly recommended that you have both a RUBY VERSION and BUNDLED WITH version listed in your Gemfile.lock. If you do not have those values, you can generate them and commit them to git:
$ bundle update --ruby
$ git add Gemfile.lock
$ git commit -m "Update Gemfile.lock"
Applications without these values specified in the Gemfile.lock may break unexpectedly when the defaults change.
This version of Bundler is not suitable for production applications. However, it can be used to test that your application is ready for the official release of Bundler 4.0.