diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 2775ad7e..570b26ee 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -5,6 +5,11 @@
 
 version: 2
 updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    target-branch: "develop"
+    schedule:
+      interval: "weekly"
   - package-ecosystem: "pip" # See documentation for possible values
     directory: "/" # Location of package manifests
     schedule:
diff --git a/.github/requirements-develop.txt b/.github/requirements-develop.txt
new file mode 100644
index 00000000..0cdf227f
--- /dev/null
+++ b/.github/requirements-develop.txt
@@ -0,0 +1,3 @@
+# Install these inside tox for checks against the development branches.
+comb-spec-searcher @ git+https://github.com/PermutaTriangle/comb_spec_searcher.git@develop
+permuta @ git+https://github.com/PermutaTriangle/Permuta.git@develop
diff --git a/.github/workflows/build-and-deploy.yml b/.github/workflows/build-and-deploy.yml
index faccd5cc..b7e1ab84 100644
--- a/.github/workflows/build-and-deploy.yml
+++ b/.github/workflows/build-and-deploy.yml
@@ -9,10 +9,10 @@ jobs:
   build-and-deploy:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v4
-    - uses: actions/setup-python@v5
+    - uses: actions/checkout@v7
+    - uses: actions/setup-python@v7
       with:
-        python-version: "3.14"
+        python-version: "3.15"
     - name: install dependencies
       run: |
         python -m pip install --upgrade pip
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 4963c6d0..b8b62fea 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -1,83 +1,87 @@
-name: tests
-
-on: [push, pull_request]
-
-jobs:
-
-  test:
-    strategy:
-      fail-fast: false
-      matrix:
-        include:
-          - python: "3.14"
-            toxenv: flake8
-            os: ubuntu-latest
-          - python: "3.14"
-            toxenv: mypy
-            os: ubuntu-latest
-          - python: "3.14"
-            toxenv: pylint
-            os: ubuntu-latest
-          - python: "3.14"
-            toxenv: black
-            os: ubuntu-latest
-
-          - python: "3.10"
-            toxenv: py310
-            os: ubuntu-latest
-          - python: "3.11"
-            toxenv: py311
-            os: ubuntu-latest
-          - python: "3.12"
-            toxenv: py312
-            os: ubuntu-latest
-          - python: "3.13"
-            toxenv: py313
-            os: ubuntu-latest
-          - python: "3.14"
-            toxenv: py314
-            os: ubuntu-latest
-
-          - python: "pypy-3.10"
-            toxenv: pypy310
-            os: ubuntu-latest
-          - python: "pypy-3.11"
-            toxenv: pypy311
-            os: ubuntu-latest
-
-          - python: "3.14"
-            toxenv: py314
-            os: macos-latest
-          - python: "3.14"
-            toxenv: py314
-            os: windows-latest
-
-    runs-on: ${{ matrix.os }}
-    steps:
-      - uses: actions/checkout@v4
-      - uses: actions/setup-python@v5
-        with:
-          python-version: ${{  matrix.python }}
-      - name: Install dependencies from develop branch
-        if: github.ref != 'refs/heads/master' && !(github.event_name == 'pull_request' && github.event.pull_request.base.ref == 'master')
-        run: |
-          echo "Installing dependencies from develop branches instead of PyPI"
-          python -m pip install git+https://github.com/PermutaTriangle/comb_spec_searcher.git@develop
-          python -m pip install git+https://github.com/PermutaTriangle/Permuta.git@develop
-
-          # Install the project in development mode to work with the new dependencies
-          python -m pip install -e .
-
-          # Verify installed versions
-          echo "Checking installed comb_spec_searcher version:"
-          python -c "import comb_spec_searcher; print(comb_spec_searcher.__version__)"
-          echo "Checking installed permuta version:"
-          python -c "import permuta; print(permuta.__version__)"
-      - name: install dependencies
-        run: python -m pip install --upgrade pip tox
-      - name: run
-        env:
-          TOXENV: ${{ matrix.toxenv }}
-        run: tox
-      - name: setup
-        run: pip install -e .
+name: tests
+
+on:
+  push:
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+
+  test:
+    timeout-minutes: 60
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - python: "3.15"
+            toxenv: flake8
+            os: ubuntu-latest
+          - python: "3.15"
+            toxenv: mypy
+            os: ubuntu-latest
+          - python: "3.15"
+            toxenv: pylint
+            os: ubuntu-latest
+          - python: "3.15"
+            toxenv: black
+            os: ubuntu-latest
+
+          - python: "3.11"
+            toxenv: py311
+            os: ubuntu-latest
+          - python: "3.12"
+            toxenv: py312
+            os: ubuntu-latest
+          - python: "3.13"
+            toxenv: py313
+            os: ubuntu-latest
+          - python: "3.14"
+            toxenv: py314
+            os: ubuntu-latest
+          - python: "3.15"
+            toxenv: py315
+            os: ubuntu-latest
+
+          - python: "pypy-3.11"
+            toxenv: pypy311
+            os: ubuntu-latest
+          - python: "pypy-3.12"
+            toxenv: pypy312
+            os: ubuntu-latest
+
+          - python: "3.15"
+            toxenv: py315
+            os: macos-latest
+          - python: "3.15"
+            toxenv: py315
+            os: windows-latest
+
+    runs-on: ${{ matrix.os }}
+    env:
+      # Release checks use PyPI; other branches test both development dependencies.
+      # tox reads this when resolving dependencies inside each test environment.
+      TILINGS_TEST_DEPS: >-
+        ${{ github.ref != 'refs/heads/master' &&
+            !(github.event_name == 'pull_request' && github.event.pull_request.base.ref == 'master') &&
+            '-r.github/requirements-develop.txt' || '' }}
+    steps:
+      - uses: actions/checkout@v7
+      - uses: actions/setup-python@v7
+        with:
+          python-version: ${{ matrix.python }}
+          cache: pip
+          cache-dependency-path: |
+            pyproject.toml
+            tox.ini
+            .github/requirements-develop.txt
+      - name: Install tox
+        run: python -m pip install --upgrade pip "tox>=4,<5"
+      - name: Run checks
+        run: python -m tox run -e ${{ matrix.toxenv }}
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index fe30c3b4..640716bf 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -1,5 +1,5 @@
 repos:
   - repo: https://github.com/psf/black
-    rev: 22.10.0
+    rev: 25.12.0
     hooks:
       - id: black
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3c317fe0..58ef3f09 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,19 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Changed
+- Minimum Python version is now 3.11; CPython and PyPy 3.10 are no longer supported.
+- Python 3.15 is the primary version for linting, packaging, and cross-platform
+  tests, with compatibility tests for CPython 3.11 through 3.14.
+- Black targets Python 3.11, the minimum supported version.
+
+### Added
+- Required CI coverage for stable PyPy 3.12 alongside PyPy 3.11.
+
+### Fixed
+- Install the dependencies of PyPy's bundled cffi and HPy packages in tox so
+  dependency checks pass.
+
 ## [4.1.0] - 2026-01-15
 ### Changed
 - new GriddedPerm.contains_patt function checks positions first, then pattern
diff --git a/README.rst b/README.rst
index 874ac7bb..19695163 100644
--- a/README.rst
+++ b/README.rst
@@ -52,6 +52,8 @@ To install ``tilings`` on your system, run:
 
        pip install tilings
 
+Python 3.11 or newer is required.
+
 If you would like to edit the source code, you should install ``tilings`` in
 development mode by cloning the repository, running
 
diff --git a/pylintrc b/pylintrc
index 0564c0cc..487b41c2 100644
--- a/pylintrc
+++ b/pylintrc
@@ -36,10 +36,6 @@ persistent=yes
 # Specify a configuration file.
 #rcfile=
 
-# When enabled, pylint would attempt to guess common misconfiguration and emit
-# user-friendly hints instead of false-positive error messages.
-suggestion-mode=yes
-
 # Allow loading of arbitrary C extensions. Extensions are imported into the
 # active Python interpreter and may run arbitrary code.
 unsafe-load-any-extension=no
@@ -517,6 +513,6 @@ preferred-modules=
 [EXCEPTIONS]
 
 # Exceptions that will emit a warning when being caught. Defaults to
-# "BaseException, Exception".
-overgeneral-exceptions=BaseException,
-                       Exception
+# "builtins.BaseException, builtins.Exception".
+overgeneral-exceptions=builtins.BaseException,
+                       builtins.Exception
diff --git a/pyproject.toml b/pyproject.toml
index cc3aa80c..5e7872cc 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -29,16 +29,17 @@ classifiers = [
     "Intended Audience :: Science/Research",
     "License :: OSI Approved :: BSD License",
     "Programming Language :: Python :: 3",
-    "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
     "Programming Language :: Python :: 3.12",
     "Programming Language :: Python :: 3.13",
+    "Programming Language :: Python :: 3.14",
+    "Programming Language :: Python :: 3.15",
     "Programming Language :: Python :: Implementation :: CPython",
     "Programming Language :: Python :: Implementation :: PyPy",
     "Topic :: Education",
     "Topic :: Scientific/Engineering :: Mathematics",
 ]
-requires-python = ">=3.10"
+requires-python = ">=3.11"
 dependencies = [
     "comb-spec-searcher>=4.2.1",
     "permuta>=2.3.0",
@@ -68,7 +69,7 @@ include = [
 ]
 
 [tool.black]
-target-version = ['py310']
+target-version = ['py311']
 include = '\.pyi?$'
 exclude = '''
 (
diff --git a/tilings/algorithms/requirement_placement.py b/tilings/algorithms/requirement_placement.py
index e5fb85d0..1a665d22 100644
--- a/tilings/algorithms/requirement_placement.py
+++ b/tilings/algorithms/requirement_placement.py
@@ -97,7 +97,7 @@ def already_placed(
             return cell in self._point_row_cells
         if self.own_col:  # Only placing in own column
             return cell in self._point_col_cells
-        raise Exception("Not placing at all!!")
+        raise ValueError("Not placing at all!!")
 
     def _point_translation(
         self, gp: GriddedPerm, index: int, placed_cell: Cell
@@ -283,7 +283,7 @@ def _farther(c1: Cell, c2: Cell, direction: Dir) -> bool:
             return c1[1] > c2[1]
         if direction == DIR_SOUTH:
             return c1[1] < c2[1]
-        raise Exception("Invalid direction")
+        raise ValueError("Invalid direction")
 
     def forced_obstructions_from_requirement(
         self,
diff --git a/tilings/strategies/factor.py b/tilings/strategies/factor.py
index 686bb468..358a47c7 100644
--- a/tilings/strategies/factor.py
+++ b/tilings/strategies/factor.py
@@ -633,7 +633,7 @@ def __str__(self) -> str:
         elif self.factor_class is FactorWithMonotoneInterleavingStrategy:
             s = "factor with monotone interleaving"
         else:
-            raise Exception("Invalid interleaving type")
+            raise ValueError("Invalid interleaving type")
         if self.unions:
             s = "unions of " + s
         if self.tracked:
diff --git a/tox.ini b/tox.ini
index 0aba2056..d229c47d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,31 +4,36 @@
 # and then run "tox" from this directory.
 
 [tox]
+minversion = 4
 envlist =
     flake8, mypy, pylint, black
-    py{310,311,312,313,314},
-    pypy{310,311}
+    py{311,312,313,314,315},
+    pypy{311,312}
 
 [default]
-basepython=python3.14
+basepython=python3.15
 
 [testenv]
 description = run test
 basepython =
-    py310: python3.10
     py311: python3.11
     py312: python3.12
     py313: python3.13
     py314: python3.14
-    pypy310: pypy3.10
+    py315: python3.15
     pypy311: pypy3.11
+    pypy312: pypy3.12
 deps =
     pytest
     pytest-timeout
+    # PyPy bundles cffi and HPy; virtualenv may omit their dependencies.
+    pycparser; platform_python_implementation == "PyPy"
+    setuptools; platform_python_implementation == "PyPy"
+    {env:TILINGS_TEST_DEPS:}
 commands =
-    pip install --force-reinstall git+https://github.com/PermutaTriangle/comb_spec_searcher.git@develop
-    pip freeze
-    pytest
+    python -m pip check
+    python -m pip freeze
+    python -m pytest {posargs}
 
 [pytest]
 addopts = --doctest-modules --doctest-ignore-import-errors
@@ -51,6 +56,7 @@ description = run pylint (static code analysis)
 basepython = {[default]basepython}
 deps =
     pylint
+    {env:TILINGS_TEST_DEPS:}
 commands = pylint tilings
 
 [testenv:mypy]
@@ -60,11 +66,13 @@ deps =
     mypy
     types-requests
     types-tabulate
+    {env:TILINGS_TEST_DEPS:}
 commands = mypy
 
 [testenv:black]
 description = check that comply with autoformating
 basepython = {[default]basepython}
+skip_install = True
 deps =
     black==25.12.0
 commands = black --check --diff .