diff --git a/.github/workflows/create-release.yml b/.github/workflows/create-release.yml
index e35982b..7f3ab71 100644
--- a/.github/workflows/create-release.yml
+++ b/.github/workflows/create-release.yml
@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: 🎉 Create release
-        uses: googleapis/release-please-action@v4
+        uses: googleapis/release-please-action@v5
         id: release
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
diff --git a/.github/workflows/testing.yml b/.github/workflows/testing.yml
index 12ee9d7..d1ccaf8 100644
--- a/.github/workflows/testing.yml
+++ b/.github/workflows/testing.yml
@@ -12,7 +12,7 @@ on:  # yamllint disable-line rule:truthy
 
 jobs:
   testing:
-    timeout-minutes: 4
+    timeout-minutes: 15
     runs-on: ${{ matrix.os }}
     env:
       COMPOSER_ROOT_VERSION: '1.x-dev'
@@ -25,6 +25,7 @@ jobs:
         os:
           - ubuntu-latest
         php-version:
+          - '8.1'
           - '8.2'
           - '8.3'
           - '8.4'
@@ -46,15 +47,25 @@ jobs:
       - name: 🤖 Validate composer.json and composer.lock
         run: composer validate --ansi --strict
 
-      # Infection is dev-only and requires PHP >= 8.3, which breaks installation
-      # on the 8.2 matrix leg. It is not needed to run the test suite.
+      # Remove unused libs
       - name: 🧹 Remove Infection (incompatible with PHP 8.2)
-        run: composer remove --dev infection/infection --no-update --no-interaction
+        run: composer remove --dev infection/infection vimeo/psalm spiral/code-style buggregator/trap testo/bridge-infection --no-update --no-interaction
 
       - name: 📥 Install dependencies with composer
+        if: matrix.php-version != '8.1'
         uses: ramsey/composer-install@v3
         with:
           dependency-versions: ${{ matrix.dependencies }}
 
+      - name: 📥 Install and downgrade for PHP 8.1
+        if: matrix.php-version == '8.1'
+        uses: php-internal/actions/downgrade@v1
+        with:
+          php-version: '8.1'
+          dependency-versions: ${{ matrix.dependencies }}
+          # Downgrade the test harness (which uses 8.2+ syntax) and the testo config, but not src:
+          # the shipped library must be exercised on 8.1 as written.
+          paths: tests testo.php
+
       - name: 🧪 Run tests
         run: composer test
diff --git a/composer.json b/composer.json
index 3ed890e..35a47b6 100644
--- a/composer.json
+++ b/composer.json
@@ -30,12 +30,12 @@
     },
     "require-dev": {
         "buggregator/trap": "^1.15",
-        "infection/infection": "^0.33.2",
+        "infection/infection": "^0.35.2",
         "llm/skills": "^1.7",
         "roxblnfk/unpoly": "^1.8.1",
         "spiral/code-style": "^2.3.1",
         "testo/bridge-infection": "^0.1.6",
-        "testo/testo": "^0.10.21",
+        "testo/testo": "^0.10.47",
         "vimeo/psalm": "^7"
     },
     "minimum-stability": "dev",