diff --git a/.github/workflows/ci_sh_def.yml b/.github/workflows/ci_sh_def.yml
index a86088642e..d18076fa6d 100644
--- a/.github/workflows/ci_sh_def.yml
+++ b/.github/workflows/ci_sh_def.yml
@@ -319,6 +319,9 @@ jobs:
           - clang: 15
             std: 20
             container_suffix: "-bullseye"
+          - clang: 16
+            std: 20
+            container_suffix: "-bullseye"
 
     name: "🐍 3 • Clang ${{ matrix.clang }} • C++${{ matrix.std }} • x64"
     container: "silkeh/clang:${{ matrix.clang }}${{ matrix.container_suffix }}"
@@ -483,6 +486,7 @@ jobs:
           - { gcc: 10, std: 17 }
           - { gcc: 11, std: 20 }
           - { gcc: 12, std: 20 }
+          - { gcc: 13, std: 20 }
 
     name: "🐍 3 • GCC ${{ matrix.gcc }} • C++${{ matrix.std }}• x64"
     container: "gcc:${{ matrix.gcc }}"
diff --git a/.github/workflows/ci_sh_def.yml.patch b/.github/workflows/ci_sh_def.yml.patch
index e62ebe36a3..d416c43483 100644
--- a/.github/workflows/ci_sh_def.yml.patch
+++ b/.github/workflows/ci_sh_def.yml.patch
@@ -1,5 +1,5 @@
---- ci.yml	2023-07-12 13:23:42.051641241 -0700
-+++ ci_sh_def.yml	2023-07-12 13:24:17.295586495 -0700
+--- ci.yml	2023-08-03 22:50:35.724639197 -0700
++++ ci_sh_def.yml	2023-08-03 22:54:28.312146852 -0700
 @@ -1,4 +1,16 @@
 -name: CI
 +# PLEASE KEEP THIS GROUP OF FILES IN SYNC AT ALL TIMES:
@@ -59,7 +59,7 @@
  
      - name: Build
        run: cmake --build build -j 2
-@@ -320,6 +336,7 @@
+@@ -323,6 +339,7 @@
          -DPYBIND11_WERROR=ON
          -DDOWNLOAD_CATCH=ON
          -DCMAKE_CXX_STANDARD=${{ matrix.std }}
@@ -67,7 +67,7 @@
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
      - name: Build
-@@ -349,7 +366,7 @@
+@@ -352,7 +369,7 @@
        run: apt-get update && DEBIAN_FRONTEND="noninteractive" apt-get install -y cmake git python3-dev python3-pytest python3-numpy
  
      - name: Configure
@@ -76,7 +76,7 @@
  
      - name: Build
        run: cmake --build build -j2 --verbose
-@@ -430,7 +447,7 @@
+@@ -433,7 +450,7 @@
          cmake3 -S . -B build -DDOWNLOAD_CATCH=ON \
                              -DCMAKE_CXX_STANDARD=11 \
                              -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)") \
@@ -85,7 +85,7 @@
                              -DPYBIND11_TEST_FILTER="test_smart_ptr.cpp"
  
      # Building before installing Pip should produce a warning but not an error
-@@ -489,6 +506,7 @@
+@@ -493,6 +510,7 @@
          -DPYBIND11_WERROR=ON
          -DDOWNLOAD_CATCH=ON
          -DCMAKE_CXX_STANDARD=${{ matrix.std }}
@@ -93,7 +93,7 @@
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
      - name: Build
-@@ -511,6 +529,7 @@
+@@ -515,6 +533,7 @@
          -DPYBIND11_WERROR=ON
          -DDOWNLOAD_CATCH=ON
          -DCMAKE_CXX_STANDARD=${{ matrix.std }}
@@ -101,7 +101,7 @@
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
          "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
  
-@@ -562,6 +581,7 @@
+@@ -566,6 +585,7 @@
          -DDOWNLOAD_CATCH=ON     \
          -DDOWNLOAD_EIGEN=OFF    \
          -DCMAKE_CXX_STANDARD=11             \
@@ -109,7 +109,7 @@
          -DCMAKE_CXX_COMPILER=$(which icpc)  \
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
-@@ -594,6 +614,7 @@
+@@ -598,6 +618,7 @@
          -DDOWNLOAD_CATCH=ON     \
          -DDOWNLOAD_EIGEN=OFF    \
          -DCMAKE_CXX_STANDARD=17             \
@@ -117,7 +117,7 @@
          -DCMAKE_CXX_COMPILER=$(which icpc)  \
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
-@@ -661,6 +682,7 @@
+@@ -665,6 +686,7 @@
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
          -DCMAKE_CXX_STANDARD=11
@@ -125,7 +125,7 @@
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
      - name: Build
-@@ -711,6 +733,7 @@
+@@ -715,6 +737,7 @@
          cmake ../pybind11-tests
          -DDOWNLOAD_CATCH=ON
          -DPYBIND11_WERROR=ON
@@ -133,7 +133,7 @@
          -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
        working-directory: /build-tests
  
-@@ -806,6 +829,7 @@
+@@ -810,6 +833,7 @@
          -DPYBIND11_WERROR=ON
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
@@ -141,7 +141,7 @@
          ${{ matrix.args }}
      - name: Build C++11
        run: cmake --build build -j 2
-@@ -860,6 +884,7 @@
+@@ -864,6 +888,7 @@
          -DPYBIND11_WERROR=ON
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
@@ -149,7 +149,7 @@
          ${{ matrix.args }}
      - name: Build C++11
        run: cmake --build build --config Debug -j 2
-@@ -900,6 +925,7 @@
+@@ -904,6 +929,7 @@
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
          -DCMAKE_CXX_STANDARD=20
@@ -157,7 +157,7 @@
  
      - name: Build C++20
        run: cmake --build build -j 2
-@@ -920,6 +946,7 @@
+@@ -924,6 +950,7 @@
          -DDOWNLOAD_CATCH=ON
          -DDOWNLOAD_EIGEN=ON
          -DCMAKE_CXX_STANDARD=20
@@ -165,7 +165,7 @@
          "-DPYBIND11_TEST_OVERRIDE=test_call_policies.cpp;test_gil_scoped.cpp;test_thread.cpp"
  
      - name: Build C++20 - Exercise cmake -DPYBIND11_TEST_OVERRIDE
-@@ -962,7 +989,7 @@
+@@ -966,7 +993,7 @@
      - name: Configure C++11
        # LTO leads to many undefined reference like
        # `pybind11::detail::function_call::function_call(pybind11::detail::function_call&&)
@@ -174,7 +174,7 @@
  
      - name: Build C++11
        run: cmake --build build -j 2
-@@ -980,7 +1007,7 @@
+@@ -984,7 +1011,7 @@
        run: git clean -fdx
  
      - name: Configure C++14
@@ -183,7 +183,7 @@
  
      - name: Build C++14
        run: cmake --build build2 -j 2
-@@ -998,7 +1025,7 @@
+@@ -1002,7 +1029,7 @@
        run: git clean -fdx
  
      - name: Configure C++17
@@ -192,7 +192,7 @@
  
      - name: Build C++17
        run: cmake --build build3 -j 2
-@@ -1065,6 +1092,7 @@
+@@ -1069,6 +1096,7 @@
            -DDOWNLOAD_EIGEN=ON
            -DCMAKE_CXX_COMPILER=clang++
            -DCMAKE_CXX_STANDARD=17
@@ -200,7 +200,7 @@
  
        - name: Build
          run: cmake --build . -j 2
-@@ -1130,6 +1158,7 @@
+@@ -1134,6 +1162,7 @@
            -DDOWNLOAD_EIGEN=ON
            -DCMAKE_CXX_COMPILER=clang++
            -DCMAKE_CXX_STANDARD=17
@@ -208,7 +208,7 @@
            -DPYTHON_EXECUTABLE=$(python3 -c "import sys; print(sys.executable)")
  
        - name: Build
-@@ -1153,6 +1182,7 @@
+@@ -1157,6 +1186,7 @@
            -DDOWNLOAD_EIGEN=ON
            -DCMAKE_CXX_COMPILER=clang++
            -DCMAKE_CXX_STANDARD=17