Default Ruby version now 3.3.9 (heroku#1624)

The [default Ruby version for new Ruby applications is 3.3.9](https://devcenter.heroku.com/articles/ruby-support#default-ruby-version-for-new-apps). You’ll only get the default if the application does not specify a Ruby version.

Heroku highly recommends specifying your desired Ruby version. You can specify a Ruby version in your `Gemfile`:

```ruby
ruby "3.3.9"
```

Once you have a Ruby version specified in your `Gemfile`, update the `Gemfile.lock` by running the following command:

```term
$ bundle update --ruby
```

Make sure you commit the results to git before attempting to deploy again:

```term
$ git add Gemfile Gemfile.lock
$ git commit -m "update ruby version"
```

Author: schneems

.github/workflows/ci.yml

@@ -39,7 +39,7 @@ jobs:
           uses: ruby/setup-ruby@v1
           with:
             bundler-cache: true
-            ruby-version: "3.3.8"
+            ruby-version: "3.3.9"
         - name: Hatchet setup
           run: bundle exec hatchet ci:setup
         - name: Run Hatchet integration tests

.github/workflows/hatchet_app_cleaner.yml

@@ -24,7 +24,7 @@ jobs:
         uses: ruby/setup-ruby@v1
         with:
           bundler-cache: true
-          ruby-version: "3.3.8"
+          ruby-version: "3.3.9"
       - name: Run Hatchet destroy
         # Only apps older than 10 minutes are destroyed, to ensure that any
         # in progress CI runs are not interrupted.

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [Unreleased]
 
+- Default Ruby version is now 3.3.9 (https://github.com/heroku/heroku-buildpack-ruby/pull/1624)
 
 ## [v315] - 2025-07-24
 

Gemfile

@@ -1,7 +1,7 @@
 source "https://rubygems.org"
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
-ruby "3.3.8"
+ruby "3.3.9"
 
 group :development, :test do
   gem "toml-rb"

Gemfile.lock

@@ -72,7 +72,7 @@ DEPENDENCIES
   toml-rb
 
 RUBY VERSION
-   ruby 3.3.8p144
+   ruby 3.3.9p170
 
 BUNDLED WITH
    2.5.22

buildpack.toml

@@ -1,6 +1,6 @@
 [buildpack]
 name = "Ruby"
-ruby_version = "3.3.8"
+ruby_version = "3.3.9"
 
 [publish.Ignore]
 files = [

changelogs/unreleased/default_v339.md

@@ -0,0 +1,22 @@
+## Default Ruby version for new apps is now 3.3.9
+
+The [default Ruby version for new Ruby applications is 3.3.9](https://devcenter.heroku.com/articles/ruby-support#default-ruby-version-for-new-apps). You’ll only get the default if the application does not specify a Ruby version.
+
+Heroku highly recommends specifying your desired Ruby version. You can specify a Ruby version in your `Gemfile`:
+
+```ruby
+ruby "3.3.9"
+```
+
+Once you have a Ruby version specified in your `Gemfile`, update the `Gemfile.lock` by running the following command:
+
+```term
+$ bundle update --ruby
+```
+
+Make sure you commit the results to git before attempting to deploy again:
+
+```term
+$ git add Gemfile Gemfile.lock
+$ git commit -m "update ruby version"
+```

changelogs/v309/default_ruby.md

@@ -5,7 +5,7 @@ The [default Ruby version for new Ruby applications is 3.3.8](https://devcenter.
 Heroku highly recommends specifying your desired Ruby version. You can specify a Ruby version in your `Gemfile`:
 
 ```ruby
-ruby "3.3.8"
+ruby "3.3.9"
 ```
 
 Once you have a Ruby version specified in your `Gemfile`, update the `Gemfile.lock` by running the following command:

lib/language_pack/ruby_version.rb

@@ -12,8 +12,8 @@ def initialize(output = "")
       end
     end
 
-    BOOTSTRAP_VERSION_NUMBER = "3.3.8".freeze
-    DEFAULT_VERSION_NUMBER = "3.3.8".freeze
+    BOOTSTRAP_VERSION_NUMBER = "3.3.9".freeze
+    DEFAULT_VERSION_NUMBER = "3.3.9".freeze
     DEFAULT_VERSION        = "ruby-#{DEFAULT_VERSION_NUMBER}".freeze
     RUBY_VERSION_REGEX     = %r{
         (?<ruby_version>\d+\.\d+\.\d+){0}