diff --git a/.github/actionlint.yml b/.github/actionlint.yml
new file mode 100644
index 00000000..444b5e98
--- /dev/null
+++ b/.github/actionlint.yml
@@ -0,0 +1,6 @@
+---
+# At the time of writing, the latest actionlint version (1.7.12) doesn't
+# recognize the ubuntu-26.04 images.
+self-hosted-runner:
+  labels:
+    - ubuntu-26.04
diff --git a/.github/workflows/super_diff.yml b/.github/workflows/super_diff.yml
index fa0a2a02..fe6c8842 100644
--- a/.github/workflows/super_diff.yml
+++ b/.github/workflows/super_diff.yml
@@ -15,19 +15,19 @@ concurrency:
   cancel-in-progress: true
 jobs:
   analyze:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     if: ${{ github.event_name == 'push' || github.event.action != 'closed' }}
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
       - name: Download actionlint
         id: download-actionlint
-        run: bash <(curl https://raw.githubusercontent.com/rhysd/actionlint/7fdc9630cc360ea1a469eed64ac6d78caeda1234/scripts/download-actionlint.bash) 1.6.23
+        run: bash <(curl https://raw.githubusercontent.com/rhysd/actionlint/7fdc9630cc360ea1a469eed64ac6d78caeda1234/scripts/download-actionlint.bash) 1.7.12
         shell: bash
       - name: Check workflow files
         run: ${{ steps.download-actionlint.outputs.executable }} -color
         shell: bash
       - name: Set up Ruby
-        uses: ruby/setup-ruby@c515ec17f69368147deb311832da000dd229d338 # v1.297.0
+        uses: ruby/setup-ruby@7f797815d8adceb1c412e7abefdd1ab4abc47a5f # v1.338.0
         with:
           bundler-cache: true # `bundle install` and cache gems.
       - name: Use Node.js
@@ -47,7 +47,7 @@ jobs:
   test:
     needs:
       - analyze
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     strategy:
       fail-fast: false
       matrix:
@@ -79,7 +79,7 @@ jobs:
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
       - name: Set up Ruby
-        uses: ruby/setup-ruby@c515ec17f69368147deb311832da000dd229d338 # v1.297.0
+        uses: ruby/setup-ruby@7f797815d8adceb1c412e7abefdd1ab4abc47a5f # v1.338.0
         with:
           ruby-version: ${{ matrix.ruby }}
           bundler-cache: true
@@ -87,7 +87,7 @@ jobs:
         run: bundle exec rake --trace
 
   ready-to-merge:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     needs:
       - analyze
       - test
@@ -95,11 +95,11 @@ jobs:
       - run: echo "Analysis and tests passed. Ready to merge."
 
   collect-release-info:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
       - name: Set up Ruby
-        uses: ruby/setup-ruby@c515ec17f69368147deb311832da000dd229d338 # v1.297.0
+        uses: ruby/setup-ruby@7f797815d8adceb1c412e7abefdd1ab4abc47a5f # v1.338.0
         with:
           bundler-cache: true
       - name: Run command
@@ -110,7 +110,7 @@ jobs:
       RELEASE_VERSION: ${{ steps.command.outputs.RELEASE_VERSION }}
 
   collect-docsite-release-info:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     needs:
       - collect-release-info
     steps:
@@ -153,7 +153,7 @@ jobs:
       HAS_DOCS_CHANGES_TO_RELEASE: ${{ steps.command.outputs.HAS_DOCS_CHANGES_TO_RELEASE }}
 
   build-docsite:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     needs:
       - analyze
       - collect-release-info
@@ -176,7 +176,7 @@ jobs:
           key: docsite-${{ github.sha }}
 
   publish-docsite:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     needs:
       - collect-release-info
       - collect-docsite-release-info
@@ -243,7 +243,7 @@ jobs:
           DOCSITE_DESTINATION_PATH: ${{ needs.collect-docsite-release-info.outputs.DOCSITE_DESTINATION_PATH }}
 
   unpublish_docsite:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     needs:
       - collect-release-info
       - collect-docsite-release-info
diff --git a/.ruby-version b/.ruby-version
index 5ae69bd5..6c165c28 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-3.2.5
+3.3.13