diff --git a/.github/workflows/actions-security.yml b/.github/workflows/actions-security.yml
index 321c1196..303c0bfa 100644
--- a/.github/workflows/actions-security.yml
+++ b/.github/workflows/actions-security.yml
@@ -24,7 +24,7 @@ jobs:
           persist-credentials: false
 
       - name: Run zizmor
-        uses: zizmorcore/zizmor-action@v0.5.6
+        uses: zizmorcore/zizmor-action@70fb788f84895a7701f5643d103d587e460b5c99 # v0.6.3
         with:
           advanced-security: false
           annotations: true
diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 07195e52..48489249 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -56,7 +56,7 @@ jobs:
           key: ${{ env.EXTENSIONS_CACHE_KEY }}
 
       - name: Cache PHP extensions
-        uses: actions/cache@v5
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6
         with:
           path: ${{ steps.extcache.outputs.dir }}
           key: ${{ steps.extcache.outputs.key }}
@@ -114,7 +114,7 @@ jobs:
           key: ${{ env.EXTENSIONS_CACHE_KEY }}
 
       - name: Cache PHP extensions
-        uses: actions/cache@v5
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6
         with:
           path: ${{ steps.extcache.outputs.dir }}
           key: ${{ steps.extcache.outputs.key }}
@@ -163,7 +163,7 @@ jobs:
           key: ${{ env.EXTENSIONS_CACHE_KEY }}
 
       - name: Cache PHP extensions
-        uses: actions/cache@v5
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6
         with:
           path: ${{ steps.extcache.outputs.dir }}
           key: ${{ steps.extcache.outputs.key }}
@@ -217,7 +217,7 @@ jobs:
           key: ${{ env.EXTENSIONS_CACHE_KEY }}
 
       - name: Cache PHP extensions
-        uses: actions/cache@v5
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6
         with:
           path: ${{ steps.extcache.outputs.dir }}
           key: ${{ steps.extcache.outputs.key }}
@@ -252,7 +252,7 @@ jobs:
 
       - name: Upload Psalm report to GitHub Code Scanning
         if: ${{ always() && hashFiles('results.sarif') != '' }}
-        uses: github/codeql-action/upload-sarif@v4.36.2
+        uses: github/codeql-action/upload-sarif@cdf488f595d80d6e07e03d4674febd5ab45fa938 # v4.37.9
         with:
           sarif_file: results.sarif
           category: psalm
@@ -318,7 +318,7 @@ jobs:
           key: ${{ env.EXTENSIONS_CACHE_KEY }}
 
       - name: Cache PHP extensions
-        uses: actions/cache@v5
+        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6
         with:
           path: ${{ steps.extcache.outputs.dir }}
           key: ${{ steps.extcache.outputs.key }}
diff --git a/.github/workflows/scorecard.yml b/.github/workflows/scorecard.yml
index db6d7a28..65376dd4 100644
--- a/.github/workflows/scorecard.yml
+++ b/.github/workflows/scorecard.yml
@@ -29,7 +29,7 @@ jobs:
           persist-credentials: false
 
       - name: Run OpenSSF Scorecard
-        uses: ossf/scorecard-action@v2.4.3
+        uses: ossf/scorecard-action@2d1146689b8cda280b9bc96326124645441f03bc # v2.4.4
         with:
           results_file: scorecard-results.json
           results_format: json
diff --git a/CHANGELOG.md b/CHANGELOG.md
index d4a0db37..de3ef689 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,17 @@ history, the old changelog, and committed file changes. Older Zemit-era entries
 are summarized where the commit history is too granular to be useful as
 release notes.
 
+## Unreleased
+
+### Changed
+
+- Raise the optional/development Guzzle baseline to `^8.2.0` and OAuth2
+  client to `^2.9.1`, the compatible provider release. Guzzle 8 uses PSR-7
+  and Promises 3 and validates request methods, headers, and options more
+  strictly; review custom HTTP integrations before updating.
+- Update the cache, CodeQL upload, OpenSSF Scorecard, and zizmor CI actions
+  and pin the upgraded versions to immutable commits.
+
 ## 3.10.8 - 2026-09-21
 
 ### Fixed
diff --git a/composer.json b/composer.json
index ae7335cf..a9cb135a 100644
--- a/composer.json
+++ b/composer.json
@@ -99,11 +99,11 @@
     "cweagans/composer-patches": "^2.0.0",
     "fakerphp/faker": "^1.24.1",
     "google/recaptcha": "^1.5",
-    "guzzlehttp/guzzle": "^7.15.3",
+    "guzzlehttp/guzzle": "^8.2.0",
     "jetbrains/phpstorm-attributes": "^1.3",
     "joshtronic/php-loremipsum": "^3.0.0",
     "league/csv": "^9.28.0",
-    "league/oauth2-client": "^2.9.0",
+    "league/oauth2-client": "^2.9.1",
     "league/oauth2-facebook": "^2.2.0",
     "league/oauth2-github": "^3.1.1",
     "league/oauth2-google": "^5.0",
@@ -133,11 +133,11 @@
     "cweagans/composer-patches": "^2.0.0",
     "fakerphp/faker": "^1.24.1",
     "google/recaptcha": "^1.5",
-    "guzzlehttp/guzzle": "^7.15.3",
+    "guzzlehttp/guzzle": "^8.2.0",
     "jetbrains/phpstorm-attributes": "^1.3",
     "joshtronic/php-loremipsum": "^3.0.0",
     "league/csv": "^9.28.0",
-    "league/oauth2-client": "^2.9.0",
+    "league/oauth2-client": "^2.9.1",
     "league/oauth2-facebook": "^2.2.0",
     "league/oauth2-github": "^3.1.1",
     "league/oauth2-google": "^5.0",