diff --git a/.github/workflows/release-to-pypi.yml b/.github/workflows/release-to-pypi.yml
index fdf3af13c..df657b36c 100644
--- a/.github/workflows/release-to-pypi.yml
+++ b/.github/workflows/release-to-pypi.yml
@@ -16,10 +16,10 @@ jobs:
     steps:
 
     - name: Check out the release commit
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Set up QEMU
-      uses: docker/setup-qemu-action@v2
+      uses: docker/setup-qemu-action@v3
       with:
         platforms: arm64
       if: runner.os == 'Linux'
@@ -27,24 +27,18 @@ jobs:
     - name: Set up Python
       uses: actions/setup-python@v4
       with:
-        python-version: '3.8'
+        python-version: '3.10'
 
     - name: Install Python packages needed for wheel build and upload
-      run: |
-        python -m pip install --upgrade pip setuptools
-        python -m pip install twine wheel
+      run: python -m pip install twine
 
     - name: Build wheels
-      uses: pypa/cibuildwheel@v2.14.1
-      env:
-        CIBW_SKIP: 'pp*'
-        CIBW_ARCHS_LINUX: "auto aarch64"
-        CIBW_ARCHS_MACOS: "auto universal2"
+      uses: pypa/cibuildwheel@v2.16.2
 
     - name: Check and upload wheels
       env:
-        TWINE_USERNAME: ${{ secrets.PYPI_USERNAME }}
-        TWINE_PASSWORD: ${{ secrets.PYPI_PASSWORD }}
+       TWINE_USERNAME: ${{ secrets.PYPI_USERNAME }}
+       TWINE_PASSWORD: ${{ secrets.PYPI_PASSWORD }}
       run: |
         python -m twine check --strict wheelhouse/*.whl
         python -m twine upload wheelhouse/*.whl
@@ -55,26 +49,23 @@ jobs:
     steps:
 
     - name: Check out the release commit
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: Set up Python
       uses: actions/setup-python@v4
       with:
-        python-version: '3.8'
+        python-version: '3.10'
 
     - name: Install Python packages needed for sdist build and upload
-      run: |
-        python -m pip install --upgrade pip setuptools
-        python -m pip install twine
+      run: python -m pip install build twine
 
     - name: Build sdist
-      run: |
-        python setup.py sdist
+      run: python -m build --sdist
 
     - name: Publish sdist to PyPI
       env:
         TWINE_USERNAME: ${{ secrets.PYPI_USERNAME }}
         TWINE_PASSWORD: ${{ secrets.PYPI_PASSWORD }}
       run: |
-        python -m twine check --strict dist/*.tar.gz
-        python -m twine upload dist/*.tar.gz
+        python -m twine check --strict dist/*
+        python -m twine upload dist/*
diff --git a/.github/workflows/run-core-traits-tests.yml b/.github/workflows/run-core-traits-tests.yml
index 26c65f650..85b2b3a24 100644
--- a/.github/workflows/run-core-traits-tests.yml
+++ b/.github/workflows/run-core-traits-tests.yml
@@ -11,19 +11,19 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest]
-        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11']
+        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12']
 
     runs-on: ${{ matrix.os }}
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python-version }}
+        allow-prereleases: true
     - name: Install local package
       run: |
-        python -m pip install --upgrade pip
         # Uninstall setuptools so that the tests will catch any accidental
         # dependence of the Traits source on setuptools. Note that in future
         # setuptools may not exist in a newly-created venv
diff --git a/.github/workflows/run-style-checks.yml b/.github/workflows/run-style-checks.yml
index 82d10f3c7..c20e5973d 100644
--- a/.github/workflows/run-style-checks.yml
+++ b/.github/workflows/run-style-checks.yml
@@ -5,22 +5,16 @@ on:
 
 jobs:
   style:
-    strategy:
-      matrix:
-        os: [ubuntu-latest]
-        python-version: ['3.8']
-
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
-    - name: Set up Python ${{ matrix.python-version }}
+    - uses: actions/checkout@v4
+    - name: Set up Python 3.10
       uses: actions/setup-python@v4
       with:
-        python-version: ${{ matrix.python-version }}
+        python-version: '3.10'
     - name: Install dependencies and local packages
       run: |
-        python -m pip install --upgrade pip
         python -m pip install flake8
         python -m pip install flake8-ets
     - name: Run style checks
diff --git a/.github/workflows/run-traits-tests.yml b/.github/workflows/run-traits-tests.yml
index ed61ff5bd..27b4e6267 100644
--- a/.github/workflows/run-traits-tests.yml
+++ b/.github/workflows/run-traits-tests.yml
@@ -5,7 +5,7 @@ on:
 - workflow_dispatch
 
 env:
-  # Temporary workaround prior to release of Traits 8.0
+  # Temporary workaround prior to release of TraitsUI 8.0
   # xref: enthought/traits#1742
   ETS_QT4_IMPORTS: 1
 
@@ -14,12 +14,12 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11']
+        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12']
 
     runs-on: ${{ matrix.os }}
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@v4
     - name: Install Linux packages for Qt support
       run: |
         sudo apt-get update
@@ -37,9 +37,9 @@ jobs:
       uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python-version }}
+        allow-prereleases: true
     - name: Install dependencies and local packages
       run: |
-        python -m pip install --upgrade pip
         python -m pip install .[test]
         python -m pip install traits-stubs/[test]
     - name: Create clean test directory
diff --git a/.github/workflows/test-documentation-build.yml b/.github/workflows/test-documentation-build.yml
index c2d122b68..50906edc8 100644
--- a/.github/workflows/test-documentation-build.yml
+++ b/.github/workflows/test-documentation-build.yml
@@ -5,23 +5,16 @@ on:
 
 jobs:
   docs:
-    strategy:
-      matrix:
-        os: [ubuntu-latest]
-        python-version: ['3.8']
-
-    runs-on: ${{ matrix.os }}
+    runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v3
-    - name: Set up Python ${{ matrix.python-version }}
+    - uses: actions/checkout@v4
+    - name: Set up Python 3.10
       uses: actions/setup-python@v4
       with:
-        python-version: ${{ matrix.python-version }}
+        python-version: '3.10'
     - name: Install dependencies and local packages
-      run: |
-        python -m pip install --upgrade pip
-        python -m pip install ".[docs]"
+      run: python -m pip install .[docs]
     - name: Build HTML documentation with Sphinx
       run: |
         cd docs
diff --git a/.github/workflows/test-from-pypi.yml b/.github/workflows/test-from-pypi.yml
index d89e315d0..5850587f9 100644
--- a/.github/workflows/test-from-pypi.yml
+++ b/.github/workflows/test-from-pypi.yml
@@ -6,12 +6,17 @@ on:
     # Run at 03:27 UTC on the 8th and 22nd of every month
     - cron: '27 3 8,22 * *'
 
+env:
+  # Temporary workaround prior to release of Traits 8.0
+  # xref: enthought/traits#1742
+  ETS_QT4_IMPORTS: 1
+
 jobs:
   test-pypi-sdist:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11']
+        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12']
         python-architecture: [x86, x64]
         exclude:
         - os: macos-latest
@@ -40,12 +45,15 @@ jobs:
       with:
         python-version: ${{ matrix.python-version }}
         architecture: ${{ matrix.python-architecture }}
-    - name: Install prerequisites
+        allow-prereleases: true
+    - name: Install test dependencies and Traits from PyPI sdist (no PySide6)
       run: |
-        python -m pip install --upgrade pip setuptools wheel
-    - name: Install Traits and test dependencies from PyPI sdist
+        python -m pip install --no-binary traits Cython numpy Sphinx traits traitsui
+      if: matrix.python-version == '3.12' || matrix.python-architecture == 'x86'
+    - name: Install test dependencies and Traits from PyPI sdist (PySide6)
       run: |
-        python -m pip install --no-binary traits traits[test]
+        python -m pip install --no-binary traits Cython numpy PySide6 Sphinx traits traitsui
+      if: matrix.python-version != '3.12' && matrix.python-architecture != 'x86'
     - name: Create clean test directory
       run: |
         mkdir testdir
@@ -60,7 +68,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest, macos-latest]
-        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11']
+        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11', '3.12']
         python-architecture: [x86, x64]
         exclude:
         - os: macos-latest
@@ -89,12 +97,15 @@ jobs:
       with:
         python-version: ${{ matrix.python-version }}
         architecture: ${{ matrix.python-architecture }}
-    - name: Install prerequisites
+        allow-prereleases: true
+    - name: Install test dependencies and Traits from PyPI wheel (no PySide6)
       run: |
-        python -m pip install --upgrade pip setuptools wheel
-    - name: Install Traits and test dependencies from PyPI wheel
+        python -m pip install --only-binary traits Cython numpy Sphinx traits traitsui
+      if: matrix.python-version == '3.12' || matrix.python-architecture == 'x86'
+    - name: Install test dependencies and Traits from PyPI wheel (PySide6)
       run: |
-        python -m pip install --only-binary traits traits[test]
+        python -m pip install --only-binary traits Cython numpy PySide6 Sphinx traits traitsui
+      if: matrix.python-version != '3.12' && matrix.python-architecture != 'x86'
     - name: Create clean test directory
       run: |
         mkdir testdir
diff --git a/CHANGES.rst b/CHANGES.rst
index 2908138e8..0144482fe 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,6 +1,22 @@
 Traits CHANGELOG
 ================
 
+Release 6.4.3
+-------------
+
+Released: 2023-10-09
+
+This is a bugfix release that fixes test failures with Sphinx 7.2 and later,
+and adds support for Python 3.12.
+
+Fixes
+~~~~~
+* Use ``pathlib.Path`` instead of ``sphinx.testing.path.path`` for Sphinx
+  7.2 and later. (#1755)
+* Fix uses of the deprecated ``datetime.utcnow`` method. (#1758)
+* Update CI and workflows for Python 3.12 support. (#1757)
+
+
 Release 6.4.2
 -------------
 
diff --git a/pyproject.toml b/pyproject.toml
index 96043e943..ea061849c 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -11,5 +11,14 @@ profile = 'black'
 line_length = 79
 order_by_type = 'False'
 
+[tool.cibuildwheel]
+skip = 'pp*'
+
+[tool.cibuildwheel.macos]
+archs = ['auto', 'universal2']
+
+[tool.cibuildwheel.linux]
+archs = ['auto', 'aarch64']
+
 [tool.pytest.ini_options]
 addopts = '--ignore=traits-stubs'
diff --git a/setup.py b/setup.py
index 81d91e591..9686bb39a 100644
--- a/setup.py
+++ b/setup.py
@@ -20,7 +20,7 @@
 # into the package source.
 MAJOR = 6
 MINOR = 4
-MICRO = 2
+MICRO = 3
 PRERELEASE = ""
 IS_RELEASED = True
 
@@ -281,6 +281,7 @@ def get_long_description():
         Programming Language :: Python :: 3.9
         Programming Language :: Python :: 3.10
         Programming Language :: Python :: 3.11
+        Programming Language :: Python :: 3.12
         Programming Language :: Python :: Implementation :: CPython
         Topic :: Scientific/Engineering
         Topic :: Software Development
@@ -313,7 +314,9 @@ def get_long_description():
             "flake8",
             "flake8-ets",
             "mypy",
-            "numpy",
+            # NumPy is not yet available for Python 3.12, but that should be
+            # fixed soon: https://github.com/numpy/numpy/issues/23808
+            "numpy; python_version < '3.12'",
             "pyface",
             # Doc builds are hanging with pygments 2.15.0 and 2.15.1.
             # Maybe related: https://github.com/pygments/pygments/issues/2427
diff --git a/traits/util/event_tracer.py b/traits/util/event_tracer.py
index 0769f315f..acb226c70 100644
--- a/traits/util/event_tracer.py
+++ b/traits/util/event_tracer.py
@@ -15,7 +15,7 @@
 import os
 import threading
 from contextlib import contextmanager
-from datetime import datetime
+from datetime import datetime, timezone
 
 from traits import trait_notifiers
 
@@ -228,7 +228,7 @@ def pre_tracer(self, obj, name, old, new, handler):
 
         """
         indent = self.indent
-        time = datetime.utcnow().isoformat(" ")
+        time = datetime.now(timezone.utc).isoformat(" ")
         container = self.container
         container.record(
             ChangeMessageRecord(
@@ -255,7 +255,7 @@ def post_tracer(self, obj, name, old, new, handler, exception=None):
         """ Record a string representation of the trait change return
 
         """
-        time = datetime.utcnow().isoformat(" ")
+        time = datetime.now(timezone.utc).isoformat(" ")
         self.indent -= 1
         indent = self.indent
         if exception:
diff --git a/traits/util/tests/test_trait_documenter.py b/traits/util/tests/test_trait_documenter.py
index d06d36d46..b51430719 100644
--- a/traits/util/tests/test_trait_documenter.py
+++ b/traits/util/tests/test_trait_documenter.py
@@ -27,7 +27,6 @@
 if sphinx is not None:
     from sphinx.ext.autodoc import ClassDocumenter, INSTANCEATTR, Options
     from sphinx.ext.autodoc.directive import DocumenterBridge
-    from sphinx.testing.path import path
     from sphinx.testing.util import SphinxTestApp
     from sphinx.util.docutils import LoggingReporter
 
@@ -37,6 +36,11 @@
         TraitDocumenter,
     )
 
+    if sphinx.version_info < (7, 2):
+        from sphinx.testing.path import path as Path
+    else:
+        from pathlib import Path
+
 
 # Configuration file content for testing.
 CONF_PY = """\
@@ -223,7 +227,7 @@ def create_directive(self):
             with open(conf_file, "w", encoding="utf-8") as f:
                 f.write(CONF_PY)
 
-            app = SphinxTestApp(srcdir=path(tmpdir))
+            app = SphinxTestApp(srcdir=Path(tmpdir))
             app.builder.env.app = app
             app.builder.env.temp_data["docname"] = "dummy"