diff --git a/.github/workflows/upstream.yml b/.github/workflows/upstream.yml
index a15861ee47..721a920281 100644
--- a/.github/workflows/upstream.yml
+++ b/.github/workflows/upstream.yml
@@ -1,4 +1,3 @@
-
 name: Upstream
 
 on:
@@ -7,108 +6,137 @@ on:
 
 concurrency:
   group: upstream-${{ github.ref }}
-  cancel-in-progress: true
+  cancel-in-progress: false
 
 env:
-  PIP_ONLY_BINARY: numpy
-  # For cmake:
-  VERBOSE: 1
+  PYTEST_TIMEOUT: 300
 
 jobs:
   standard:
-    name: "🐍 3.11 latest internals • ubuntu-latest • x64"
+    name: "🐍 3.12 latest • ubuntu-latest • x64"
     runs-on: ubuntu-latest
+
+    # Hint: Select the 'python dev' label in the PR web view.
     if: "contains(github.event.pull_request.labels.*.name, 'python dev')"
 
     steps:
+    - name: Show env
+      run: env
+
     - uses: actions/checkout@v3
 
-    - name: Setup Python 3.11
+    - name: Setup Python 3.12
       uses: actions/setup-python@v4
       with:
-        python-version: "3.11-dev"
+        python-version: "3.12-dev"
 
-    - name: Setup Boost (Linux)
-      if: runner.os == 'Linux'
+    - name: Setup Boost
       run: sudo apt-get install libboost-dev
 
     - name: Update CMake
       uses: jwlawson/actions-setup-cmake@v1.13
 
-    - name: Prepare env
+    - name: Run pip installs
       run: |
-        python -m pip install -r tests/requirements.txt
+        python -m pip install --upgrade pip
+        python -m pip install --prefer-binary -r tests/requirements.txt
+    #   python -m pip install --prefer-binary numpy  # SLOW
+    #   python -m pip install --prefer-binary scipy  # FAILED ~Nov 2022
+
+    - name: Show platform info
+      run: python -m platform
 
-    - name: Setup annotations on Linux
-      if: runner.os == 'Linux'
-      run: python -m pip install pytest-github-actions-annotate-failures
+    - name: Show CMake version
+      run: cmake --version
 
-    # First build - C++11 mode and inplace
+    # FIRST BUILD
     - name: Configure C++11
       run: >
-        cmake -S . -B .
+        cmake -S . -B build11
+        -DCMAKE_VERBOSE_MAKEFILE=ON
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=11
+        -DCMAKE_BUILD_TYPE=Debug
 
     - name: Build C++11
-      run: cmake --build . -j 2
+      run: cmake --build build11 -j 2
 
     - name: Python tests C++11
-      run: cmake --build . --target pytest -j 2
-
-    - name: C++11 tests
-      run: cmake --build .  --target cpptest -j 2
+      run: cmake --build build11 --target pytest -j 2
+
+    # python-3.12.0-alpha.1-linux-22.04-x64.tar.gz  PASSED
+    # python-3.12.0-alpha.2-linux-22.04-x64.tar.gz  FAILED
+    # python-3.12.0-alpha.3-linux-22.04-x64.tar.gz  FAILED
+    #     free(): invalid pointer
+    #     Custom PyConfig
+    #     /home/runner/work/pybind11/pybind11/tests/test_embed/test_interpreter.cpp:175
+    #     /home/runner/work/pybind11/pybind11/tests/test_embed/test_interpreter.cpp:179: FAILED:
+    # gdb traceback points here:
+    #     https://github.com/python/cpython/blame/54289f85b2af1ecf046089ddf535dda1bdf6af24/Python/import.c#L524
+    # - name: C++ tests C++11
+    #   run: cmake --build build11 --target cpptest -j 2
 
     - name: Interface test C++11
-      run: cmake --build . --target test_cmake_build
+      run: cmake --build build11 --target test_cmake_build
 
     - name: Clean directory
       run: git clean -fdx
 
-    # Second build - C++17 mode and in a build directory
+    # SECOND BUILD
     - name: Configure C++17
       run: >
-        cmake -S . -B build2
+        cmake -S . -B build17
+        -DCMAKE_VERBOSE_MAKEFILE=ON
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=17
-        ${{ matrix.args }}
-        ${{ matrix.args2 }}
+        -DCMAKE_BUILD_TYPE=Debug
+
+    - name: Build C++17
+      run: cmake --build build17 -j 2
 
-    - name: Build
-      run: cmake --build build2 -j 2
+    - name: Python tests C++17
+      run: cmake --build build17 --target pytest
 
-    - name: Python tests
-      run: cmake --build build2 --target pytest
+    # - name: C++ tests C++17
+    #   run: cmake --build build17 --target cpptest
 
-    - name: C++ tests
-      run: cmake --build build2 --target cpptest
+    - name: Interface test C++17
+      run: cmake --build build17 --target test_cmake_build
 
-    # Third build - C++17 mode with unstable ABI
-    - name: Configure (unstable ABI)
+    - name: Clean directory
+      run: git clean -fdx
+
+    # THIRD BUILD
+    - name: Configure C++17 max DPYBIND11_INTERNALS_VERSION
       run: >
-        cmake -S . -B build3
+        cmake -S . -B build17max
+        -DCMAKE_VERBOSE_MAKEFILE=ON
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         -DCMAKE_CXX_STANDARD=17
+        -DCMAKE_BUILD_TYPE=Debug
         -DPYBIND11_INTERNALS_VERSION=10000000
-        "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
-        ${{ matrix.args }}
 
-    - name: Build (unstable ABI)
-      run: cmake --build build3 -j 2
+    - name: Build C++17 max DPYBIND11_INTERNALS_VERSION
+      run: cmake --build build17max -j 2
+
+    - name: Python tests C++17 max DPYBIND11_INTERNALS_VERSION
+      run: cmake --build build17max --target pytest
 
-    - name: Python tests (unstable ABI)
-      run: cmake --build build3 --target pytest
+    # - name: C++ tests C++17 max DPYBIND11_INTERNALS_VERSION
+    #   run: cmake --build build17max --target cpptest
 
-    - name: Interface test
-      run: cmake --build build3 --target test_cmake_build
+    - name: Interface test C++17 max DPYBIND11_INTERNALS_VERSION
+      run: cmake --build build17max --target test_cmake_build
 
-    # This makes sure the setup_helpers module can build packages using
-    # setuptools
+    # Ensure the setup_helpers module can build packages using setuptools
     - name: Setuptools helpers test
       run: pytest tests/extra_setuptools
+
+    - name: Clean directory
+      run: git clean -fdx