[EXPERIMENTAL] Drop C++11 and C++14 support

.appveyor.yml

@@ -39,7 +39,7 @@ build_script:
 - cmake -G "%CMAKE_GENERATOR%" -A "%CMAKE_ARCH%"
     -DPython_ROOT_DIR="%PYTHON_ROOT%"
     -DCMAKE_MAP_IMPORTED_CONFIG_DEBUG=Release
-    -DCMAKE_CXX_STANDARD=14
+    -DCMAKE_CXX_STANDARD=17
     -DPYBIND11_WERROR=ON
     -DDOWNLOAD_CATCH=ON
     -DCMAKE_SUPPRESS_REGENERATION=1

.github/workflows/ci.yml

@@ -40,7 +40,7 @@ jobs:
         include:
           - runs-on: ubuntu-22.04
             python-version: '3.9'
-            cmake-args: -DPYBIND11_FINDPYTHON=OFF -DPYBIND11_NUMPY_1_ONLY=ON
+            cmake-args: -DPYBIND11_FINDPYTHON=OFF
           - runs-on: ubuntu-latest
             python-version: '3.13'
             cmake-args: -DCMAKE_CXX_STANDARD=23 -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON
@@ -58,7 +58,7 @@ jobs:
             cmake-args: -DCMAKE_CXX_STANDARD=20
           - runs-on: macos-latest
             python-version: '3.14'
-            cmake-args: -DCMAKE_CXX_STANDARD=14
+            cmake-args: -DCMAKE_CXX_STANDARD=17
           - runs-on: windows-2022
             python-version: '3.9'
             cmake-args: -DPYBIND11_FINDPYTHON=OFF
@@ -88,18 +88,18 @@ jobs:
             cmake-args: -DPYBIND11_TEST_SMART_HOLDER=ON -DPYBIND11_SIMPLE_GIL_MANAGEMENT=ON
           - runs-on: ubuntu-latest
             python-version: '3.14'
-            cmake-args: -DCMAKE_CXX_STANDARD=14
+            cmake-args: -DCMAKE_CXX_STANDARD=17
           - runs-on: ubuntu-latest
             python-version: '3.15t'
             cmake-args: -DCMAKE_CXX_STANDARD=17 -DPYBIND11_TEST_SMART_HOLDER=ON
 
           # No SciPy for macOS ARM
           - runs-on: macos-15-intel
             python-version: '3.9'
-            cmake-args: -DCMAKE_CXX_STANDARD=14
+            cmake-args: -DCMAKE_CXX_STANDARD=17
           - runs-on: macos-15-intel
             python-version: '3.13'
-            cmake-args: -DCMAKE_CXX_STANDARD=11
+            cmake-args: -DCMAKE_CXX_STANDARD=17
           - runs-on: macos-latest
             python-version: '3.12'
             cmake-args: -DCMAKE_CXX_STANDARD=17 -DPYBIND11_DISABLE_HANDLE_TYPE_NAME_DEFAULT_IMPLEMENTATION=ON
@@ -119,7 +119,7 @@ jobs:
             cmake-args: -DPYBIND11_TEST_SMART_HOLDER=ON
           - runs-on: windows-2022
             python-version: '3.9'
-            cmake-args: -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DPYBIND11_NUMPY_1_ONLY=ON
+            cmake-args: -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded
           # This needs a python built with MTd
           # - runs-on: windows-2022
           #   python-version: '3.11'
@@ -152,7 +152,7 @@ jobs:
       python-version: ${{ matrix.python-version }}
       cmake-args: ${{ matrix.cmake-args }}
 
-  # This checks inplace builds with C++11
+  # This checks inplace builds with C++17.
   inplace:
     if: github.event.pull_request.draft == false
     strategy:
@@ -166,7 +166,7 @@ jobs:
           - runs-on: windows-latest
             python-version: '3.11'
 
-    name: "🐍 ${{ matrix.python-version }} • ${{ matrix.runs-on }} • x64 inplace C++14"
+    name: "🐍 ${{ matrix.python-version }} • ${{ matrix.runs-on }} • x64 inplace C++17"
     runs-on: ${{ matrix.runs-on }}
     timeout-minutes: 90
 
@@ -202,7 +202,7 @@ jobs:
         -DPYBIND11_PYTEST_ARGS=-v
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_STANDARD=14
+        -DCMAKE_CXX_STANDARD=17
         -DPYBIND11_INTERNALS_VERSION=10000000
 
     # Checks to makes sure defining `_` is allowed
@@ -254,12 +254,15 @@ jobs:
         run: uv tool install ninja
 
       - name: Configure via preset
-        run: cmake --preset venv -DPYBIND11_CREATE_WITH_UV="${{ matrix.python-version }}"
+        run: >
+          cmake --preset venv
+          -DPYBIND11_CREATE_WITH_UV="${{ matrix.python-version }}"
+          -DCMAKE_CXX_STANDARD=17
 
-      - name: Build C++11
+      - name: Build C++17
         run: cmake --build --preset venv
 
-      - name: Python tests C++11
+      - name: Python tests C++17
         run: cmake --build --preset testsvenv -t pytest
 
   # Testing on clang using the excellent silkeh clang docker images
@@ -270,10 +273,11 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - clang: 5
-            std: 14
+          # Clang 11 is the oldest LLVM toolchain available on a Debian base
+          # that meets pybind11's current Python and CMake requirements.
           - clang: 11
-            std: 20
+            std: 17
+            container_suffix: "-bullseye"
           - clang: 16
             std: 20
             container_suffix: "-bullseye"
@@ -333,7 +337,12 @@ jobs:
       run: apt-get update && DEBIAN_FRONTEND="noninteractive" apt-get install -y cmake git python3-dev python3-pytest python3-numpy
 
     - name: Configure
-      run: cmake -S . -B build -DPYBIND11_CUDA_TESTS=ON -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
+      run: >
+        cmake -S . -B build
+        -DPYBIND11_CUDA_TESTS=ON
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DCMAKE_CXX_STANDARD=17
 
     - name: Build
       run: cmake --build build -j2 --verbose
@@ -371,7 +380,7 @@ jobs:
 #      run: |
 #        source /etc/profile.d/modules.sh
 #        module load /opt/nvidia/hpc_sdk/modulefiles/nvhpc/20.11
-#        cmake -S . -B build -DDOWNLOAD_CATCH=ON -DCMAKE_CXX_STANDARD=14 -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
+#        cmake -S . -B build -DDOWNLOAD_CATCH=ON -DCMAKE_CXX_STANDARD=17 -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 #
 #    - name: Build
 #      run: cmake --build build -j 2 --verbose
@@ -536,44 +545,6 @@ jobs:
         set +e; source /opt/intel/oneapi/setvars.sh; set -e
         python3 -m pip install -r tests/requirements.txt
 
-    - name: Configure C++11
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake -S . -B build-11     \
-        -DPYBIND11_WERROR=ON    \
-        -DDOWNLOAD_CATCH=ON     \
-        -DDOWNLOAD_EIGEN=OFF    \
-        -DCMAKE_CXX_STANDARD=11             \
-        -DCMAKE_CXX_COMPILER=$(which icpc)  \
-        -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
-
-    - name: Build C++11
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake --build build-11 -j 2 -v
-
-    - name: Python tests C++11
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        sudo service apport stop
-        cmake --build build-11 --target check
-
-    - name: C++ tests C++11
-      timeout-minutes: 3
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake --build build-11 --target cpptest
-
-    - name: Interface test C++11
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake --build build-11 --target test_cmake_build
-
-    - name: Visibility test
-      run: |
-        set +e; source /opt/intel/oneapi/setvars.sh; set -e
-        cmake --build build-11 --target test_cross_module_rtti
-
     - name: Configure C++17
       run: |
         set +e; source /opt/intel/oneapi/setvars.sh; set -e
@@ -659,7 +630,7 @@ jobs:
         -DPYBIND11_WERROR=ON
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
-        -DCMAKE_CXX_STANDARD=11
+        -DCMAKE_CXX_STANDARD=17
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 
     - name: Build
@@ -701,6 +672,7 @@ jobs:
       run: >
         cmake .
         -DPYBIND11_INSTALL=1 -DPYBIND11_TEST=0
+        -DCMAKE_CXX_STANDARD=17
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
 
     - name: Make and install
@@ -717,6 +689,7 @@ jobs:
         cmake ../pybind11-tests
         -DDOWNLOAD_CATCH=ON
         -DPYBIND11_WERROR=ON
+        -DCMAKE_CXX_STANDARD=17
         -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
       working-directory: /build-tests
 
@@ -772,6 +745,7 @@ jobs:
           - python: '3.9'
             args: -DCMAKE_CXX_STANDARD=17
           - python: '3.13'
+            args: -DCMAKE_CXX_STANDARD=17
 
 
     name: "🐍 ${{ matrix.python }} • MSVC 2022 • x86 ${{ matrix.args }}"
@@ -810,7 +784,7 @@ jobs:
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         ${{ matrix.args }}
-    - name: Build C++11
+    - name: Build C++17
       run: cmake --build build -j 2
 
     - name: Python tests
@@ -859,7 +833,7 @@ jobs:
         -DDOWNLOAD_CATCH=ON
         -DDOWNLOAD_EIGEN=ON
         ${{ matrix.args }}
-    - name: Build C++11
+    - name: Build C++20
       run: cmake --build build --config Debug -j 2
 
     - name: Python tests
@@ -969,80 +943,30 @@ jobs:
 
     - uses: actions/checkout@v7
 
-    - name: Configure C++11
+    - name: Configure C++17
       # LTO leads to many undefined reference like
       # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
       run: >-
-        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=11 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
+        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
         -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
         -S . -B build
 
-    - name: Build C++11
+    - name: Build C++17
       run: cmake --build build -j 2
 
-    - name: Python tests C++11
+    - name: Python tests C++17
       run: cmake --build build --target pytest -j 2
 
-    - name: C++11 tests
+    - name: C++17 tests
       timeout-minutes: 3
       run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build --target cpptest -j 2
 
-    - name: Interface test C++11
+    - name: Interface test C++17
       run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build --target test_cmake_build
 
     - name: Visibility test
       run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build --target test_cross_module_rtti
 
-    - name: Clean directory
-      run: git clean -fdx
-
-    - name: Configure C++14
-      run: >-
-        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=14 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
-        -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
-        -S . -B build2
-
-    - name: Build C++14
-      run: cmake --build build2 -j 2
-
-    - name: Python tests C++14
-      run: cmake --build build2 --target pytest -j 2
-
-    - name: C++14 tests
-      timeout-minutes: 3
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build2 --target cpptest -j 2
-
-    - name: Interface test C++14
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build2 --target test_cmake_build
-
-    - name: Visibility test
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build2 --target test_cross_module_rtti
-
-    - name: Clean directory
-      run: git clean -fdx
-
-    - name: Configure C++17
-      run: >-
-        cmake -G "MinGW Makefiles" -DCMAKE_CXX_STANDARD=17 -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
-        -DPYTHON_EXECUTABLE=$(python -c "import sys; print(sys.executable)")
-        -S . -B build3
-
-    - name: Build C++17
-      run: cmake --build build3 -j 2
-
-    - name: Python tests C++17
-      run: cmake --build build3 --target pytest -j 2
-
-    - name: C++17 tests
-      timeout-minutes: 3
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build3 --target cpptest -j 2
-
-    - name: Interface test C++17
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build3 --target test_cmake_build
-
-    - name: Visibility test
-      run: PYTHONHOME=/${{matrix.sys}} PYTHONPATH=/${{matrix.sys}} cmake --build build3 --target test_cross_module_rtti
-
   windows_clang:
     if: github.event.pull_request.draft == false
 

.github/workflows/configure.yml

@@ -71,7 +71,11 @@ jobs:
     # These steps use a directory with a space in it intentionally
     - name: Configure
       shell: bash
-      run: cmake -S. -B"build dir" -DPYBIND11_WERROR=ON -DDOWNLOAD_CATCH=ON
+      run: >
+        cmake -S. -B"build dir"
+        -DPYBIND11_WERROR=ON
+        -DDOWNLOAD_CATCH=ON
+        -DCMAKE_CXX_STANDARD=17
 
     # Only build and test if this was manually triggered in the GitHub UI
     - name: Build

.github/workflows/reusable-standard.yml

@@ -78,6 +78,7 @@ jobs:
           -DPYBIND11_PYTEST_ARGS=-v
           -DDOWNLOAD_CATCH=ON
           -DDOWNLOAD_EIGEN=ON
+          -DCMAKE_CXX_STANDARD=17
           -DPYTHON_EXECUTABLE=${{ steps.python.outputs.python-path }}
           ${{ inputs.cmake-args }}
 

.github/workflows/tests-cibw.yml

@@ -15,6 +15,9 @@ concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
+env:
+  CIBW_CONFIG_SETTINGS: "cmake.define.CMAKE_CXX_STANDARD=17"
+
 jobs:
   build-wasm-emscripten:
     name: Pyodide wheel