diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index b44ad7fe..484c7dbf 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -6,6 +6,10 @@ on:
     tags:
       - 'v*'
   pull_request:
+  schedule:
+    # run every Monday at 5am UTC
+    - cron: '0 5 * * 1'
+  workflow_dispatch:
 
 jobs:
 
@@ -16,8 +20,8 @@ jobs:
       matrix:
         os: [ubuntu-latest]
         python-version: ["3.9", "3.10", "3.11", "3.12", "3.13"]
-        sphinx: [">=5,<9"]  # Newest Sphinx (any)
-        myst-parser: [">=1,<3"]  # Newest MyST Parser (any)
+        sphinx: [""]  # Newest Sphinx (any)
+        myst-parser: [""]  # Newest MyST Parser (any)
         include:
           # Just check the other platforms once
           - os: windows-latest
@@ -57,12 +61,12 @@ jobs:
     - name: Install myst-nb with Sphinx ${{ matrix.sphinx }}
       shell: bash
       run: |
-        pip install --upgrade pip
         # Temporary: for python 3.13 we need the nightly pyarrow wheels
         if [[ ${{ matrix.python-version }} == '3.13' ]] ; then
           PIP_EXTRA_INDEX_URL=https://pypi.anaconda.org/scientific-python-nightly-wheels/simple pip install --pre pyarrow
         fi
         pip install --upgrade "Sphinx${{ matrix.sphinx }}" "myst-parser${{ matrix.myst-parser }}" -e .[testing]
+        pip freeze
 
     - name: Run pytest
       run: pytest --durations=10
@@ -80,8 +84,8 @@ jobs:
         cache: pip
     - name: Install dependencies
       run: |
-        pip install --upgrade pip
         pip install -e .[testing]
+        pip freeze
 
     - name: Run pytest
       run: pytest --durations=10 --cov=myst_nb --cov-report=xml --cov-report=term-missing
diff --git a/.github/workflows/tests_devdeps.yml b/.github/workflows/tests_devdeps.yml
new file mode 100644
index 00000000..3a3743e2
--- /dev/null
+++ b/.github/workflows/tests_devdeps.yml
@@ -0,0 +1,36 @@
+name: continuous-integration-devdeps
+
+on:
+  push:
+    branches: [master]
+  schedule:
+    # run every Monday at 5am UTC
+    - cron: '0 5 * * 1'
+  workflow_dispatch:
+
+jobs:
+
+  tests:
+
+    strategy:
+      fail-fast: false
+      matrix:
+        sphinx: [""]  # Newest Sphinx (any)
+        myst-parser: [""]  # Newest MyST Parser (any)
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up Python 3.12
+      uses: actions/setup-python@v5
+      with:
+        python-version: "3.12"
+        cache: pip
+    - name: Install myst-nb with development Sphinx and myst-parser versions
+      run: |
+        pip install --upgrade pip
+        pip install --upgrade git+https://github.com/executablebooks/MyST-Parser.git#egg=myst-parser git+https://github.com/sphinx-doc/sphinx.git#egg=sphinx -e .[testing]
+
+    - name: Run pytest
+      run: pytest --durations=10
diff --git a/tox.ini b/tox.ini
index ed46aa30..dc5edcf0 100644
--- a/tox.ini
+++ b/tox.ini
@@ -31,10 +31,11 @@ deps =
     ipython
 setenv =
     BUILDER = {env:BUILDER:html}
-whitelist_externals =
+allowlist_externals =
     echo
     rm
 commands =
+    pip freeze
     clean: rm -rf docs/_build
     sphinx-build {posargs} -nW --keep-going -b {env:BUILDER} docs/ docs/_build/{env:BUILDER}
 commands_post = echo "open file://{toxinidir}/docs/_build/{env:BUILDER}/index.html"