diff --git a/.coveragerc b/.coveragerc
deleted file mode 100644
index c1d6ccd3e6..0000000000
--- a/.coveragerc
+++ /dev/null
@@ -1,45 +0,0 @@
-[run]
-source = arch
-branch = True
-omit =
-    */_version.py
-    */compat/*
-    # Scripts that simulate and fit the critical values
-    */critical_values/simulation/*
-plugins = Cython.Coverage
-
-[report]
-# Regexes for lines to exclude from consideration
-exclude_lines =
-    # Have to re-enable the standard pragma
-    pragma: no cover
-
-    # Don't complain if tests don't hit defensive assertion code:
-    raise NotImplementedError
-    except NotImplementedError
-    # Ignore pass
-    pass
-    # Ignore failure messages
-    pytest.xfail
-    # Ignore ImportError protection
-    except ImportError
-    # Ignore type checking code
-    if TYPE_CHECKING
-    elif TYPE_CHECKING
-    # Cython function declarations
-    cdef
-    # Cython functions with void
-    cdef void
-    # Numba jit decorators
-    @jit
-
-
-include = */arch/*
-omit =
-    */_version.py
-    */compat/*
-    # Scripts that simulate and fit the critical values
-    */critical_values/simulation/*
-    *recursions.py
-    *samplers.py
-ignore_errors = True
diff --git a/.flake8 b/.flake8
deleted file mode 100644
index 0417842f92..0000000000
--- a/.flake8
+++ /dev/null
@@ -1,4 +0,0 @@
-[flake8]
-# Leave at 99 for now
-max-line-length = 99
-ignore = E203,W503,BLK100
diff --git a/.gitattributes b/.gitattributes
deleted file mode 100644
index f5a58b76e9..0000000000
--- a/.gitattributes
+++ /dev/null
@@ -1 +0,0 @@
-arch/_version.py export-subst
diff --git a/.github/workflows/generate-documentation.yml b/.github/workflows/generate-documentation.yml
index b0fdea1912..0e490b2197 100644
--- a/.github/workflows/generate-documentation.yml
+++ b/.github/workflows/generate-documentation.yml
@@ -34,8 +34,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        python -m pip install -r requirements.txt
-        python -m pip install -r requirements-dev.txt
+        python -m pip install --group dev --group doc
 
     - name: Install arch
       run: |
diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
index 033cf8ae20..fbea753f10 100644
--- a/.github/workflows/lint.yml
+++ b/.github/workflows/lint.yml
@@ -8,8 +8,8 @@ on:
 
 jobs:
   lint:
-    # The oldest and the newest supported Python. flake8 and black parse the code with
-    # the grammar of the Python that runs them.
+    # The oldest and the newest supported Python. black parses the code with the grammar
+    # of the Python that runs it.
     name: Lint, Python ${{ matrix.python-version }}
     runs-on: ubuntu-latest
     defaults:
@@ -27,19 +27,16 @@ jobs:
         with:
           python-version: ${{ matrix.python-version }}
 
+      # The lint dependency group in pyproject.toml
       - name: Install the linters
         id: install
         run: |
           python -m pip install --upgrade pip
-          python -m pip install black flake8 isort ruff "numpydoc>=1.10"
+          python -m pip install --group lint
           python -m pip list
 
       # Every check runs even when an earlier one fails, so that the log shows all of
       # the problems
-      - name: flake8
-        if: ${{ !cancelled() && steps.install.outcome == 'success' }}
-        run: flake8 arch
-
       - name: ruff
         if: ${{ !cancelled() && steps.install.outcome == 'success' }}
         run: ruff check arch
diff --git a/.github/workflows/windows-arm.yml b/.github/workflows/windows-arm.yml
index a6aa8fc9b9..4b3a11a3e7 100644
--- a/.github/workflows/windows-arm.yml
+++ b/.github/workflows/windows-arm.yml
@@ -64,17 +64,18 @@ jobs:
           python -c "import platform, sys; print(sys.version, platform.machine())"
           python -c "import sys, sysconfig; print(sysconfig.get_platform()); sys.exit(sysconfig.get_platform() != 'win-arm64')"
 
-      # Only wheels, so that the job fails if a dependency would have to be compiled
+      # Only wheels, so that the job fails if a dependency would have to be compiled. The
+      # test requirements are the test dependency group in pyproject.toml.
       - name: Install the dependencies
         env:
           NUMBA: ${{ matrix.numba }}
         run: |
-          packages=(numpy scipy pandas statsmodels matplotlib seaborn "pytest>=9,<10" pytest-xdist)
+          packages=(numpy scipy pandas statsmodels matplotlib seaborn)
           if [[ "${NUMBA}" == "true" ]]; then
             packages+=(numba)
           fi
           python -m pip install --upgrade pip
-          python -m pip install --only-binary=:all: "${packages[@]}"
+          python -m pip install --only-binary=:all: --group test "${packages[@]}"
 
       - name: Build the wheel
         run: |
diff --git a/README.md b/README.md
index 4e0cb6d79d..69e83d5442 100644
--- a/README.md
+++ b/README.md
@@ -266,14 +266,19 @@ Building the extensions from source needs the Visual Studio Build Tools
 
 ### Developing
 
-The development requirements are:
-
-- Cython (3.1+), meson-python and ninja, unless building without the binary
-  modules
-- pytest (9+, for tests)
-- sphinx (to build docs)
-- sphinx-immaterial (to build docs)
-- jupyter, notebook and nbsphinx (to build docs)
+The development requirements are dependency groups in `pyproject.toml`,
+which pip 25.1 or later installs. From a clone of the repository,
+
+```shell
+python -m pip install --group dev
+python -m pip install -e . --no-build-isolation
+```
+
+installs the tools to build (Cython 3.1+, meson-python and ninja), test
+(pytest 9+) and lint arch, and then arch itself. Adding `--group doc` to the
+first command also installs what the documentation needs (sphinx,
+sphinx-immaterial and nbsphinx). `doc/source/contributing.rst` lists the
+commands that check the code.
 
 ### Installation Notes
 
diff --git a/arch/unitroot/critical_values/simulation/requirements.txt b/arch/unitroot/critical_values/simulation/requirements.txt
deleted file mode 100644
index 2322d57dd7..0000000000
--- a/arch/unitroot/critical_values/simulation/requirements.txt
+++ /dev/null
@@ -1,3 +0,0 @@
-joblib
-colorama
-psutil
diff --git a/ci/azure/azure_template_posix.yml b/ci/azure/azure_template_posix.yml
index a708e9e1b8..9c252848ac 100644
--- a/ci/azure/azure_template_posix.yml
+++ b/ci/azure/azure_template_posix.yml
@@ -212,7 +212,7 @@ jobs:
 
   - script: |
       echo "Testing editable install"
-      export COVERAGE_OPTS="--cov-config=.coveragerc --cov=arch --cov-branch --cov-report xml:coverage.xml --cov-report term"
+      export COVERAGE_OPTS="--cov=arch --cov-branch --cov-report xml:coverage.xml --cov-report term"
       echo pytest -m "${PYTEST_PATTERN}" --junitxml=junit/test-results.xml -n auto --durations=25 ${COVERAGE_OPTS} arch/tests
       pytest -m "${PYTEST_PATTERN}" --junitxml=junit/test-results.xml -n auto --durations=25 ${COVERAGE_OPTS} arch/tests
     displayName: 'Run tests (editable)'
@@ -230,7 +230,7 @@ jobs:
       echo "Testing with Cython coverage"
       # Uninstall xdist to avoid issues with coverage and Cython
       python -m pip uninstall pytest-xdist -y || true
-      export COVERAGE_OPTS="--cov-config=.coveragerc --cov=arch --cov-branch --cov-report xml:coverage.xml --cov-report term"
+      export COVERAGE_OPTS="--cov=arch --cov-branch --cov-report xml:coverage.xml --cov-report term"
       echo pytest --junitxml=junit/test-results.xml --durations=25 ${COVERAGE_OPTS} arch/tests/univariate/test_recursions.py arch/tests/bootstrap/test_samplers.py arch/tests/univariate/test_arch_in_mean.py
       pytest --junitxml=junit/test-results.xml --durations=25 ${COVERAGE_OPTS} arch/tests/univariate/test_recursions.py arch/tests/bootstrap/test_samplers.py arch/tests/univariate/test_arch_in_mean.py
     displayName: 'Run tests (cython coverage)'
diff --git a/ci/azure/azure_template_windows.yml b/ci/azure/azure_template_windows.yml
index cdadb1edfd..3441b492a0 100644
--- a/ci/azure/azure_template_windows.yml
+++ b/ci/azure/azure_template_windows.yml
@@ -18,11 +18,14 @@ jobs:
   strategy:
     # The newest Python with the newest packages, and the oldest Python with numpy 1.x
     # (the default integer is 32 bits on Windows) and pandas 2.1. PACKAGES is installed
-    # in a single pip command with requirements.txt, so that pip also picks versions
-    # of the other packages that work with the pins.
+    # in a single pip command with the build and test dependency groups in
+    # pyproject.toml, so that pip also picks versions of the other packages that work
+    # with the pins. pip installs scipy, pandas and statsmodels with arch when PACKAGES
+    # does not list them.
     matrix:
       python314_win_latest:
         python.version: '3.14'
+        PACKAGES: 'matplotlib seaborn'
       python310_win_numpy126:
         python.version: '3.10'
         PACKAGES: 'numpy==1.26.4 scipy==1.11.4 pandas==2.1.4 statsmodels==0.14.1 matplotlib seaborn numba build'
@@ -40,9 +43,8 @@ jobs:
   - script: |
       python -m venv arch-test
       call arch-test\Scripts\activate.bat
-      python -m pip install --upgrade pip wheel
-      python -m pip install -r requirements-dev.txt -U
-      python -m pip install %PACKAGES% -r requirements.txt -U || exit /b 1
+      python -m pip install --upgrade pip
+      python -m pip install --group build --group test %PACKAGES% -U || exit /b 1
       python -m pip list
     displayName: 'Create Venv and Install dependencies'
 
diff --git a/ci/azure/install-posix.sh b/ci/azure/install-posix.sh
index 8620605079..416708f5d4 100644
--- a/ci/azure/install-posix.sh
+++ b/ci/azure/install-posix.sh
@@ -1,5 +1,9 @@
 #!/usr/bin/env bash
 
+# The build tools, the test requirements and the packages that the example notebooks
+# need are dependency groups in pyproject.toml, which pip 25.1 or later installs
+DEP_GROUPS=(--group build --group test --group notebooks)
+
 if [[ ${USE_CONDA} == "true" ]]; then
   # Miniforge (conda-forge only) is installed by the pipeline and the env's bin
   # directory is on PATH, so no activation is needed.
@@ -13,16 +17,15 @@ if [[ ${USE_CONDA} == "true" ]]; then
   fi
   CMD="mamba install -n arch-test -y -c conda-forge numpy"
 else
-  CMD="python -m pip install numpy"
+  CMD="python -m pip install ${DEP_GROUPS[*]} numpy"
 fi
 
-python -m pip install --upgrade pip "setuptools>=61" wheel
-python -m pip install cython "pytest>=9,<10" pytest-xdist "coverage[toml]" pytest-cov ipython jupyter notebook nbconvert "property_cached>=1.6.3" nbconvert setuptools_scm colorama "meson-python>=0.18.0" meson ninja "numpydoc>=1.10"
-
+python -m pip install --upgrade pip
 
 # Versions are exact so that the job tests what its matrix entry says, and all of
-# the packages are installed in a single command so that the installer picks
-# versions of matplotlib, seaborn, ... that work with them
+# the packages (with pip, also the dependency groups) are installed in a single
+# command so that the installer picks versions of matplotlib, seaborn, ... that work
+# with them
 if [[ -n ${NUMPY} ]]; then CMD="$CMD==${NUMPY}"; fi;
 CMD="$CMD scipy"
 if [[ -n ${SCIPY} ]]; then CMD="$CMD==${SCIPY}"; fi;
@@ -47,6 +50,12 @@ CMD="$CMD $EXTRA"
 echo $CMD
 eval $CMD || exit 1
 
+if [[ ${USE_CONDA} == "true" ]]; then
+  # After the conda packages, so that pip keeps the numpy from conda-forge
+  echo python -m pip install "${DEP_GROUPS[@]}"
+  python -m pip install "${DEP_GROUPS[@]}" || exit 1
+fi
+
 if [[ ${NO_MATPLOTLIB,,} == true ]]; then
   # Fail if another package installed matplotlib, so that the job really tests without it
   if python -c "import importlib.util, sys; sys.exit(importlib.util.find_spec('matplotlib') is None)"; then
diff --git a/doc/requirements.txt b/doc/requirements.txt
deleted file mode 100644
index 9258b8671b..0000000000
--- a/doc/requirements.txt
+++ /dev/null
@@ -1,25 +0,0 @@
-wheel
-meson-python
-ninja
-setuptools_scm[toml]>=9.2,<10
-cython>=3.1.0
-numpy >=2
-scipy >=1.15.0
-ipython >=8.0.1
-matplotlib >=3.9
-pandas >=2.3.0
-statsmodels >=0.14.5
-jinja2
-sphinx
-seaborn
-numpydoc>=1.0.0
-nbsphinx
-sphinx-immaterial
-jupyter
-notebook
-sphinx-autodoc-typehints
-fonttools>=4.62.0 # not directly required, pinned by Snyk to avoid a vulnerability
-jupyterlab>=4.4.8 # not directly required, pinned by Snyk to avoid a vulnerability
-nbconvert>=7.17.0 # not directly required, pinned by Snyk to avoid a vulnerability
-jupyter-server>=2.20.0 # not directly required, pinned by Snyk to avoid a vulnerability
-tornado>=6.5.7 # not directly required, pinned by Snyk to avoid a vulnerability
diff --git a/doc/source/changes/9.0.rst b/doc/source/changes/9.0.rst
index a43e00660a..868008eeb6 100644
--- a/doc/source/changes/9.0.rst
+++ b/doc/source/changes/9.0.rst
@@ -1314,6 +1314,13 @@ Documentation and maintenance
   test suite, including the slow tests, on Python 3.13 to 3.15. Unlike the other jobs,
   it does not limit the number of BLAS threads, because NumPy's OpenBLAS on this
   platform crashes with one thread (see "Compatibility") (:issue:`1003`).
+- The development requirements are dependency groups in ``pyproject.toml``, which pip
+  25.1 or later installs, for example with ``python -m pip install --group dev`` (see
+  the contributing guide). They replace ``requirements.txt``, ``requirements-dev.txt``
+  and ``doc/requirements.txt``, and the ``test``, ``doc`` and ``dev`` extras, which have
+  been removed. The settings of coverage moved from ``.coveragerc`` to
+  ``pyproject.toml``, and ruff replaces flake8 in the style checks, with the same limit
+  of 99 characters on comments, docstrings and long strings (:issue:`1021`).
 
 Deprecations and removals
 ~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/doc/source/contributing.rst b/doc/source/contributing.rst
index 5646f58e3c..7a3f4e1a6d 100644
--- a/doc/source/contributing.rst
+++ b/doc/source/contributing.rst
@@ -1,6 +1,47 @@
 Contributing
 ============
 
+Development environment
+-----------------------
+
+The development requirements are dependency groups (PEP 735) in ``pyproject.toml``,
+which pip 25.1 or later installs. From the root of a clone of the repository,
+
+.. code-block:: bash
+
+   python -m pip install --group dev
+   python -m pip install -e . --no-build-isolation
+
+installs the build tools, the test runner, the linters and the packages that the example
+notebooks need, and then builds and installs arch in place. Add ``--group doc`` to the
+first command to also build the documentation. The groups are:
+
+* ``build``: what ``python -m pip install -e . --no-build-isolation`` needs (Cython,
+  meson, meson-python, ninja, NumPy and setuptools-scm).
+* ``test``: pytest, pytest-xdist, pytest-cov and numpydoc.
+* ``notebooks``: jupyter and nbconvert, which the slow tests use to run the example
+  notebooks.
+* ``lint``: ruff, black, isort, numpydoc, mypy and the pandas and SciPy stubs.
+* ``docstrings``: numpydoc, which ``test`` and ``lint`` include.
+* ``dev``: ``build``, ``test``, ``lint`` and ``notebooks``, with matplotlib, seaborn and
+  pytest-randomly.
+* ``doc``: Sphinx, sphinx-immaterial and nbsphinx, in addition to ``dev``.
+* ``simulation``: the packages that the scripts in
+  ``arch/unitroot/critical_values/simulation`` need in addition to ``dev``.
+
+The groups do not include the dependencies of arch, which pip installs with arch. The
+tests and the checks that CI runs are
+
+.. code-block:: bash
+
+   python -m pytest arch/tests -n auto -m "not slow"
+   ruff check arch
+   black --check arch
+   isort --check arch
+   python -m numpydoc lint $(git ls-files "arch/*.py")
+
+and the settings of all of these tools are in ``pyproject.toml``.
+
 Docstrings
 ----------
 
@@ -115,8 +156,8 @@ The rules are configured in the ``[tool.numpydoc_validation]`` table of
    python -m numpydoc lint $(git ls-files "arch/*.py")
    python -m pytest arch/tests/test_docstrings.py
 
-Both need numpydoc 1.10 or later, which ``requirements-dev.txt`` and the ``dev`` extra
-install. The Lint workflow runs the first command, and the second is skipped when
+Both need numpydoc 1.10 or later, which the ``test``, ``lint`` and ``dev`` dependency
+groups install. The Lint workflow runs the first command, and the second is skipped when
 numpydoc is not installed.
 
 ``numpydoc lint`` reads the source files. It cannot see a docstring that a class
diff --git a/pyproject.toml b/pyproject.toml
index 787045f8a7..d20f4293a3 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,15 +1,17 @@
 [build-system]
 build-backend = 'mesonpy'
+# The build dependency group below repeats these pins (other than NumPy's) for builds
+# without build isolation, since a dependency group cannot include this table.
+# meson.build also checks the Cython floor.
 requires = [
-  'meson-python',
-  "cython>=3.1.0,<4",  # Sync with the doc and dev extras and requirements-dev.txt
+  "meson-python>=0.18.0",
+  "cython>=3.1.0,<4",
   "numpy>=2.0.0,<3",
-  "setuptools_scm>=9.2.0,<10",
+  "setuptools-scm>=9.2.0,<10",
 ]
 
 [project]
 name = "arch"
-# Keep synced with requirements.txt
 dependencies = [
   "numpy>=1.22.3,<3",
   "pandas>=1.4.0",
@@ -33,6 +35,7 @@ classifiers = [
   "Operating System :: Microsoft :: Windows",
   "Operating System :: POSIX",
   "Programming Language :: Python",
+  "Programming Language :: Python :: 3 :: Only",
   "Programming Language :: Cython",
   "Topic :: Scientific/Engineering",
 ]
@@ -67,101 +70,105 @@ maintainers = [
 readme = "README.md"
 requires-python = ">=3.10"
 
-[project.optional-dependencies]
-test = [
-  # test
-  "pytest>=9,<10",
-  "pytest-randomly",
-  "pytest-xdist",
-  "pytest-cov",
-  "coverage[toml]",
-  "meson",
+[project.urls]
+homepage = "https://github.com/bashtage/arch"
+documentation = "https://bashtage.github.io/arch/"
+repository = "https://github.com/bashtage/arch"
+issues = "https://github.com/bashtage/arch/issues"
+changelog = "https://bashtage.github.io/arch/changes.html"
+
+# Development dependencies (PEP 735), installed with pip 25.1 or later. For example,
+#   python -m pip install --group dev
+#   python -m pip install -e . --no-build-isolation
+# installs everything needed to build, test and lint arch, and adding "--group doc" to
+# the first command also installs what the documentation needs. The groups do not
+# include the dependencies of arch, which pip installs with arch.
+[dependency-groups]
+# Everything that "python -m pip install -e . --no-build-isolation" needs
+build = [
+  "cython>=3.1.0,<4",
+  "meson>=1.9.0",  # meson_version in meson.build
+  "meson-python>=0.18.0",
   "ninja",
+  "numpy",  # Its range is in the dependencies of arch
+  "setuptools-scm>=9.2.0,<10",
 ]
-doc = [
-  # Documentation
-  "setuptools>=61",
-  "wheel",
-  "setuptools_scm[toml]>=9.2.0,<10",
-  "cython>=3.1.0,<4",  # Sync with the doc and dev extras and requirements-dev.txt
-  "numpy >=2.3.4",
-  "scipy >=1.16.0",
-  "ipython >=8.0.1",
-  "matplotlib >=3.10",
-  "patsy >=0.5.3",
-  "statsmodels >=0.13.5",
-  "jinja2",
-  "sphinx>=7",
-  "seaborn",
+# numpydoc checks the docstrings, in "python -m numpydoc lint" and in
+# arch/tests/test_docstrings.py
+docstrings = [
   "numpydoc>=1.10",
-  "nbsphinx",
-  "sphinx-immaterial",
+]
+# The test runner and the docstring checks. Without matplotlib and seaborn, the tests of
+# the plots are skipped, and CI tests both with and without them. numba runs the
+# recursions only when arch is built without the Cython extensions.
+test = [
+  "pytest>=9",  # minversion in [tool.pytest]
+  "pytest-cov",
+  "pytest-xdist",
+  "coverage[toml]",  # Python 3.10 needs the extra to read [tool.coverage]
+  { include-group = "docstrings" },
+]
+# The example notebooks, which the slow tests in arch/tests/test_examples.py run and the
+# documentation shows
+notebooks = [
+  "ipython>=8",
   "jupyter",
+  "nbconvert>=7.17.0",
   "notebook",
-  "sphinx-autodoc-typehints",
-  "fonttools>=4.43.0", # not directly required, pinned by Snyk to avoid a vulnerability
-  "jupyterlab>=4.4.8", # not directly required, pinned by Snyk to avoid a vulnerability
-  "ipython>=7",
-  "sphinx_immaterial",
-  "nbconvert",
-  "pickleshare",
-  # Requirements for doc build, in addition to requirements.txt
-  "pandas~=2.3.3",
+  "jupyter-server>=2.20.0",  # not directly required, pinned by Snyk to avoid a vulnerability
+  "jupyterlab>=4.4.8",  # not directly required, pinned by Snyk to avoid a vulnerability
+  "tornado>=6.5.7",  # not directly required, pinned by Snyk to avoid a vulnerability
+]
+lint = [
+  "black[jupyter]~=26.10.1",
+  "isort~=9.0",
+  "mypy>=1.3",
+  "pandas-stubs",
+  "ruff>=0.17.4",
+  "scipy-stubs",
+  { include-group = "docstrings" },
 ]
 dev = [
-  # versioning
-  "setuptools_scm[toml]>=9.2.0,<10",
-  "packaging",
-  # Performance
-  "cython>=3.1.0",
-  "numba>=0.55",
-  # Graphics
+  { include-group = "build" },
+  { include-group = "test" },
+  { include-group = "lint" },
+  { include-group = "notebooks" },
   "matplotlib>=3",
   "seaborn",
-  # Tests
-  "pytest>=9,<10",
   "pytest-randomly",
-  "pytest-xdist",
-  "pytest-cov",
-  # docstrings: the numpydoc linter and arch/tests/test_docstrings.py
-  "numpydoc>=1.10",
-  # formatting
-  "black[jupyter]~=25.9.0",
-  "isort~=6.0",
+  "fonttools>=4.62.0",  # not directly required, pinned by Snyk to avoid a vulnerability
+  "urllib3>=2.8.0",  # not directly required, pinned by Snyk to avoid a vulnerability
+  "zipp>=3.19.1",  # not directly required, pinned by Snyk to avoid a vulnerability
+]
+# The documentation, in addition to the dev group
+doc = [
+  "nbsphinx",
+  "pickleshare",
+  "sphinx>=7",
+  "sphinx-immaterial",
+]
+# The scripts in arch/unitroot/critical_values/simulation that simulate the critical
+# values, in addition to the dev group
+simulation = [
   "colorama",
-  "flake8",
-  "flake8-bugbear",
-  "mypy>=1.3",
-  "pandas-stubs",
-  "scipy-stubs",
-  "ruff>=0.8.6",
-  "pyupgrade>=3.4.0",
-  "jupyterlab-code-formatter",
-  "jupyterlab>=4.4.8",  # not directly required, pinned by Snyk to avoid a vulnerability
-  "zipp>=3.19.1", # not directly required, pinned by Snyk to avoid a vulnerability
+  "joblib",
+  "psutil",
 ]
 
-
-[project.urls]
-homepage = "https://github.com/bashtage/arch"
-documentation = "https://bashtage.github.io/arch/"
-repository = "https://github.com/bashtage/arch"
-changelog = "https://bashtage.github.io/arch/changes.html"
-
 [tool.meson-python.args]
 setup = ['--vsenv']
 
 [tool.setuptools_scm]
 version_file = "arch/_version.py"
 
+# black and ruff take their target Python versions from requires-python
 [tool.black]
-target-version = ['py310']
 exclude = '''
 (
   \.egg
   | \.git
   | \.mypy_cache
-  | \.oytest_cache
+  | \.pytest_cache
   | buck-out
   | ^/build/
   | ^/dist/
@@ -177,7 +184,6 @@ exclude = [
 [tool.ruff]
 line-length = 88
 fix = false
-target-version = "py310"
 
 [tool.ruff.lint]
 typing-modules = ["arch._typing"]
@@ -240,8 +246,6 @@ ignore = [
   # Required to allow black formatting
   # Whitespace before ':' (Needed for black)
   "E203",
-  # Line too long (### > 88 characters) (Needed for black)
-  "E501",
   # Multiple statements on one line (colon) (E701)
   "E701",
   # Always ignore
@@ -304,6 +308,11 @@ ignore = [
   "PLR0917",
 ]
 
+# black keeps code within 88 characters but cannot shorten comments, docstrings and long
+# strings. E501 limits every line to 99 characters, as flake8 did.
+[tool.ruff.lint.pycodestyle]
+max-line-length = 99
+
 [tool.ruff.lint.per-file-ignores]
 # Has function names test for running test suite, not a (pytest) )test
 "arch/utility/__init__.py" = ["PT028"]
@@ -389,7 +398,8 @@ omit = [
 
 [tool.coverage.report]
 show_missing = true
-ignore_errors = false
+# Report on the other files when one cannot be read
+ignore_errors = true
 # Regexes for lines to exclude from consideration
 exclude_also = [
   # Have to re-enable the standard pragma
@@ -448,14 +458,6 @@ disallow_untyped_defs=true
 disallow_incomplete_defs=true
 show_error_context=true
 
-[tool.mypy-arch.conftest]
-check_untyped_defs=false
-disallow_untyped_defs=false
-
-[tool.mypy-arch._version]
-check_untyped_defs=false
-disallow_untyped_defs=false
-
 [[tool.mypy.overrides]]
 module = "arch.tests.*"
 check_untyped_defs=false
@@ -463,16 +465,11 @@ disallow_untyped_defs=false
 disallow_incomplete_defs=false
 
 [[tool.mypy.overrides]]
-module = ["conftest", "arch.conftest"]
+module = ["conftest", "arch.conftest", "arch._version"]
 check_untyped_defs=false
 disallow_untyped_defs=false
 disallow_incomplete_defs=false
 
-[tool.pyrefly]
-project-excludes = ["**/tests*"]
-preset = "legacy"
-ignore-missing-imports = ["*"]
-
 [[tool.mypy.overrides]]
 module = [
   "unitroot.critical_values.simulation.*",
@@ -482,6 +479,11 @@ check_untyped_defs=false
 disallow_untyped_defs=false
 disallow_incomplete_defs=false
 
+[tool.pyrefly]
+project-excludes = ["**/tests*"]
+preset = "legacy"
+ignore-missing-imports = ["*"]
+
 [tool.numpydoc_validation]
 # Run with ``python -m numpydoc lint $(git ls-files "arch/*.py")``.  "all" with other
 # codes listed is "everything except those codes".
diff --git a/requirements-dev.txt b/requirements-dev.txt
deleted file mode 100644
index 21bd955465..0000000000
--- a/requirements-dev.txt
+++ /dev/null
@@ -1,56 +0,0 @@
-# versioning
-meson-python>=0.18.0
-meson
-ninja
-setuptools_scm[toml]>=9.2.0,<10
-packaging
-
-# Performance
-cython>=3.1.0
-numba>=0.49,!=0.50.*;python_version<"3.12"
-
-# Graphics
-matplotlib>=3
-seaborn
-
-# Tests
-pytest>=9,<10
-pytest-xdist
-pytest-cov
-pytest-randomly
-
-# docstrings: the numpydoc linter and arch/tests/test_docstrings.py
-numpydoc>=1.10
-
-# formatting
-black[jupyter]~=25.1.0
-isort~=5.12
-colorama
-flake8
-flake8-bugbear
-mypy
-ruff>=0.8.6
-pyupgrade>=3.4.0
-jupyterlab-code-formatter
-
-# Documentation
-ipython>=7
-sphinx>=7
-sphinx_immaterial
-nbsphinx
-jupyter
-notebook
-nbconvert
-sphinx-autodoc-typehints
-pickleshare
-jupyterlab>=4.4.8 # not directly required, pinned by Snyk to avoid a vulnerability
-zipp>=3.19.1 # not directly required, pinned by Snyk to avoid a vulnerability
-urllib3>=2.8.0 # not directly required, pinned by Snyk to avoid a vulnerability
-fonttools>=4.62.0 # not directly required, pinned by Snyk to avoid a vulnerability
-jupyter-server>=2.20.0 # not directly required, pinned by Snyk to avoid a vulnerability
-tornado>=6.5.7 # not directly required, pinned by Snyk to avoid a vulnerability
-
-
-# typing
-pandas-stubs
-scipy-stubs
diff --git a/requirements.txt b/requirements.txt
deleted file mode 100644
index 4dba3fa5f2..0000000000
--- a/requirements.txt
+++ /dev/null
@@ -1,6 +0,0 @@
-# Keep synced with pyproject.toml
-numpy>=1.22.3
-scipy>=1.8
-pandas>=1.4
-statsmodels>=0.13.1
-packaging
\ No newline at end of file