diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
new file mode 100644
index 0000000..b3b9f44
--- /dev/null
+++ b/.github/workflows/ci.yaml
@@ -0,0 +1,50 @@
+name: CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.9", "3.11", "3.12"]
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Install uv
+      uses: astral-sh/setup-uv@v5
+      with:
+        python-version: ${{ matrix.python-version }}
+
+    - name: Install the project
+      run: uv sync --dev
+
+    - name: Run tests
+      run: uv run pytest
+
+  lint:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Install uv
+      uses: astral-sh/setup-uv@v5
+      with:
+        python-version: "3.12"
+
+    - name: Install the project
+      run: uv sync --dev
+
+    - name: MyPy type checking
+      run: uv run mypy src/
+
+    - name: Lint with ruff
+      run: |
+        uv run ruff check .
+        uv run ruff format --check .
diff --git a/pyproject.toml b/pyproject.toml
index 8aa3110..a021ef4 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -49,5 +49,5 @@ select = ["E", "F", "I", "B", "UP"]
 testpaths = ["tests"]
 
 [tool.mypy]
-python_version = "3.9"
+python_version = "3.10"
 ignore_missing_imports = true
diff --git a/src/structree/_config.py b/src/structree/_config.py
index 39252c7..ba73287 100644
--- a/src/structree/_config.py
+++ b/src/structree/_config.py
@@ -12,7 +12,7 @@
 
 from __future__ import annotations
 
-from typing import Annotated, Literal, Optional, Type, TypeVar, Union
+from typing import Annotated, Literal, Type, TypeVar, Union
 
 from pydantic import BaseModel, ConfigDict, Field
 
@@ -83,7 +83,7 @@ class StructConfig(BaseModel):
 
     model_config = ConfigDict(arbitrary_types_allowed=True)
 
-    def __init_subclass__(cls, type: Optional[str] = None, **kwargs):
+    def __init_subclass__(cls, type: str | None = None, **kwargs):
         super().__init_subclass__(**kwargs)
         if type is not None:
             cls.__annotations__ = {"type": Literal[type], **cls.__annotations__}
diff --git a/src/structree/_flatten_util.py b/src/structree/_flatten_util.py
index b556207..4870a5f 100644
--- a/src/structree/_flatten_util.py
+++ b/src/structree/_flatten_util.py
@@ -229,5 +229,5 @@ def _unravel_list(indices, shapes, from_dtypes, to_dtype, arr):
     chunks = np.split(arr, indices[:-1])
     return [
         chunk.reshape(shape).astype(dtype)
-        for chunk, shape, dtype in zip(chunks, shapes, from_dtypes, strict=False)
+        for chunk, shape, dtype in zip(chunks, shapes, from_dtypes)
     ]
diff --git a/src/structree/_registry.py b/src/structree/_registry.py
index 43b5ef9..5cf6844 100644
--- a/src/structree/_registry.py
+++ b/src/structree/_registry.py
@@ -15,7 +15,7 @@
 import dataclasses
 from collections import OrderedDict
 from collections.abc import Callable, Sequence
-from typing import Any, NamedTuple, Optional, TypeVar
+from typing import Any, NamedTuple, TypeVar
 
 Typ = TypeVar("Typ", bound=type[Any])
 
@@ -102,7 +102,7 @@ def _dict_to_iter(d: dict):
 
 
 def _dict_from_iter(keys, vals):
-    return dict(zip(keys, vals, strict=False))
+    return dict(zip(keys, vals))
 
 
 register_struct(dict, _dict_to_iter, _dict_from_iter)
@@ -110,7 +110,7 @@ def _dict_from_iter(keys, vals):
 
 # OrderedDict
 def _od_from_iter(keys, vals):
-    return OrderedDict(zip(keys, vals, strict=False))
+    return OrderedDict(zip(keys, vals))
 
 
 register_struct(OrderedDict, _dict_to_iter, _od_from_iter)
@@ -118,8 +118,8 @@ def _od_from_iter(keys, vals):
 
 def register_dataclass(
     nodetype: Typ,
-    data_fields: Optional[Sequence[str]] = None,
-    meta_fields: Optional[Sequence[str]] = None,
+    data_fields: Sequence[str] | None = None,
+    meta_fields: Sequence[str] | None = None,
     drop_fields: Sequence[str] = (),
 ) -> Typ:
     """
@@ -227,8 +227,8 @@ def register_dataclass(
             raise ValueError(msg)
 
     def unflatten_func(meta, data):
-        meta_args = tuple(zip(meta_fields, meta, strict=False))
-        data_args = tuple(zip(data_fields, data, strict=False))
+        meta_args = tuple(zip(meta_fields, meta))
+        data_args = tuple(zip(data_fields, data))
         kwargs = dict(meta_args + data_args)
         return nodetype(**kwargs)
 
diff --git a/src/structree/_struct.py b/src/structree/_struct.py
index 7d82471..da475af 100644
--- a/src/structree/_struct.py
+++ b/src/structree/_struct.py
@@ -33,7 +33,7 @@
 import functools
 from collections.abc import Callable
 from dataclasses import InitVar, fields, replace
-from typing import Any, Optional, TypeVar, Union
+from typing import Any, TypeVar
 
 from typing_extensions import dataclass_transform
 
@@ -55,7 +55,7 @@
 def field(
     static: bool = False,
     *,
-    metadata: Optional[dict[str, Any]] = None,
+    metadata: dict[str, Any] | None = None,
     **kwargs,
 ) -> dataclasses.Field:
     """
@@ -107,7 +107,7 @@ def field(
 
 
 @dataclass_transform(field_specifiers=(field,))  # type: ignore[literal-required]
-def struct(cls: Optional[T] = None, **kwargs) -> Union[T, Callable]:
+def struct(cls: T | None = None, **kwargs) -> T | Callable:
     """
     Decorator to convert a class into a tree-compatible frozen dataclass.
 
diff --git a/src/structree/_tree_util.py b/src/structree/_tree_util.py
index f15e126..884f968 100644
--- a/src/structree/_tree_util.py
+++ b/src/structree/_tree_util.py
@@ -15,7 +15,6 @@
     TYPE_CHECKING,
     Any,
     NamedTuple,
-    Optional,
     TypeVar,
     cast,
 )
@@ -32,7 +31,7 @@
 
 
 class TreeDef(NamedTuple):
-    node_data: Optional[tuple[type, Hashable]]
+    node_data: None | tuple[type, Hashable]
     children: tuple[TreeDef, ...]
     num_leaves: int
 
@@ -64,7 +63,7 @@ def __eq__(self, other: object) -> bool:
 # Flatten/unflatten functions
 #
 def tree_flatten(
-    x: Tree, is_leaf: Optional[Callable[[Any], bool]] = None
+    x: Tree, is_leaf: Callable[[Any], bool] | None = None
 ) -> tuple[list[ArrayLike], TreeDef]:
     """
     Flatten a tree into a list of leaves and a treedef.
@@ -113,7 +112,7 @@ def tree_flatten(
 
 
 def _tree_flatten(
-    x: Tree, is_leaf: Optional[Callable[[Any], bool]]
+    x: Tree, is_leaf: Callable[[Any], bool] | None
 ) -> tuple[Iterable, TreeDef]:
     if x is None:
         return [], NONE_DEF
@@ -197,7 +196,7 @@ def _tree_unflatten(treedef: TreeDef, xs: Iterator) -> Tree:
 #
 
 
-def tree_structure(tree: Tree, is_leaf: Optional[Callable[[Any], bool]] = None) -> TreeDef:
+def tree_structure(tree: Tree, is_leaf: Callable[[Any], bool] | None = None) -> TreeDef:
     """
     Extract the structure of a tree without the leaf values.
 
@@ -227,7 +226,7 @@ def tree_structure(tree: Tree, is_leaf: Optional[Callable[[Any], bool]] = None)
 
 
 def tree_leaves(
-    tree: Tree, is_leaf: Optional[Callable[[Any], bool]] = None
+    tree: Tree, is_leaf: Callable[[Any], bool] | None = None
 ) -> list[ArrayLike]:
     """
     Extract all leaf values from a tree.
@@ -254,7 +253,7 @@ def tree_leaves(
     return flat
 
 
-def tree_all(tree: Tree, is_leaf: Optional[Callable[[Any], bool]] = None) -> bool:
+def tree_all(tree: Tree, is_leaf: Callable[[Any], bool] | None = None) -> bool:
     """
     Check if all leaves in the tree evaluate to True.
 
@@ -284,7 +283,7 @@ def tree_map(
     f: Callable,
     tree: T,
     *rest: tuple[T, ...],
-    is_leaf: Optional[Callable[[Any], bool]] = None,
+    is_leaf: Callable[[Any], bool] | None = None,
 ) -> T:
     """
     Apply a function to each leaf in a tree.
@@ -343,7 +342,7 @@ def tree_map(
             )
         flat.append(r_flat)
 
-    flat = [f(*args) for args in zip(*flat, strict=False)]
+    flat = [f(*args) for args in zip(*flat)]
     tree_out: T = tree_unflatten(treedef, flat)  # type: ignore
     return tree_out
 
@@ -352,7 +351,7 @@ def tree_reduce(
     function: Callable[[V, ArrayLike], V],
     tree: Tree,
     initializer: V,
-    is_leaf: Optional[Callable[[Any], bool]] = None,
+    is_leaf: Callable[[Any], bool] | None = None,
 ) -> V:
     """
     Reduce a tree to a single value using a function and initializer.
diff --git a/tests/test_config.py b/tests/test_config.py
index dc1e866..f4f97f6 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -13,7 +13,7 @@ class _VariantBase:
     pass
 
 
-@struct(kw_only=True)
+@struct
 class _VariantA(_VariantBase):
     param: float
 
@@ -21,7 +21,7 @@ def __call__(self):
         return self.param
 
 
-@struct(kw_only=True)
+@struct
 class _VariantB(_VariantBase):
     param: float
 
diff --git a/tests/test_ravel.py b/tests/test_ravel.py
index ec0d952..fd85ff0 100644
--- a/tests/test_ravel.py
+++ b/tests/test_ravel.py
@@ -7,11 +7,12 @@
 import numpy as np
 import pytest
 
-# Symbolic leaves come from Archimedes (dev dependency).
+# Symbolic leaves come from Archimedes (dev dependency, requires Python 3.11+).
+archimedes = pytest.importorskip("archimedes", reason="archimedes not available")
 from archimedes._core import SymbolicArray, compile, sym  # noqa: E402
 
-import structree as tree
-from structree import field, struct
+import structree as tree  # noqa: E402
+from structree import field, struct  # noqa: E402
 
 
 class TestRavel:
diff --git a/tests/test_struct.py b/tests/test_struct.py
index 76cfff5..39a9736 100644
--- a/tests/test_struct.py
+++ b/tests/test_struct.py
@@ -66,7 +66,7 @@
 
 def assert_flat_equal(f1, f2):
     assert len(f1) == len(f2)
-    for a, b in zip(f1, f2, strict=False):
+    for a, b in zip(f1, f2):
         if isinstance(a, np.ndarray):
             assert np.allclose(a, b)
         else:
@@ -284,6 +284,10 @@ class Point5:
             y: float
 
 
+@pytest.mark.skipif(
+    __import__("sys").version_info < (3, 10),
+    reason="kw_only requires Python 3.10+",
+)
 def test_register_struct_decorator():
     @struct(kw_only=True)
     class Point: