diff --git a/docs/developing/grass.py b/docs/developing/grass.py
index e3238082..7470cf11 100644
--- a/docs/developing/grass.py
+++ b/docs/developing/grass.py
@@ -2,7 +2,6 @@
 import enum
 from collections.abc import Hashable, Sequence
 from functools import cached_property
-from typing import Optional
 
 import numpy
 import xarray
@@ -33,7 +32,7 @@ class Grass(DimensionConvention[GrassGridKind, GrassIndex]):
     default_grid_kind = GrassGridKind.field
 
     @classmethod
-    def check_dataset(cls, dataset: xarray.Dataset) -> Optional[int]:
+    def check_dataset(cls, dataset: xarray.Dataset) -> int | None:
         # A Grass dataset is recognised by the 'Conventions' global attribute
         if dataset.attrs['Conventions'] == 'Grass 1.0':
             return Specificity.HIGH
diff --git a/docs/roles.py b/docs/roles.py
index c29279e3..dcae1549 100644
--- a/docs/roles.py
+++ b/docs/roles.py
@@ -1,6 +1,6 @@
 import re
-from collections.abc import Iterable
-from typing import Callable, cast
+from collections.abc import Callable, Iterable
+from typing import cast
 
 import yaml
 from docutils import nodes, utils
@@ -81,7 +81,7 @@ class Citation(Directive):
 
     def load_citation_file(self) -> dict:
         citation_file = self.options['citation_file']
-        with open(citation_file, 'r') as f:
+        with open(citation_file) as f:
             return cast(dict, yaml.load(f, yaml.Loader))
 
     def run(self) -> list[nodes.Node]:
diff --git a/scripts/min_deps_check.py b/scripts/min_deps_check.py
index 1d6fbc48..86a5a794 100755
--- a/scripts/min_deps_check.py
+++ b/scripts/min_deps_check.py
@@ -55,7 +55,7 @@ def parse_requirements(
 
     Yield (package name, major version, minor version, patch version)
     """
-    for line_number, line in enumerate(open(fname, 'r'), start=1):
+    for line_number, line in enumerate(open(fname), start=1):
         if '#' in line:
             line = line[:line.index('#')]
         line = line.strip()
diff --git a/scripts/release.py b/scripts/release.py
index 57682339..b9211941 100644
--- a/scripts/release.py
+++ b/scripts/release.py
@@ -6,7 +6,6 @@
 import shlex
 import subprocess
 import sys
-from typing import Optional
 
 PROJECT = pathlib.Path(__file__).parent.parent
 
@@ -29,7 +28,7 @@
 
 
 def main(
-    args: Optional[list[str]] = None,
+    args: list[str] | None = None,
 ) -> None:
     parser = argparse.ArgumentParser()
     add_options(parser)
@@ -222,7 +221,7 @@ def output(*args: str) -> bytes:
 
 def yn(
     prompt: str,
-    default: Optional[bool] = None,
+    default: bool | None = None,
 ) -> bool:
     examples = {True: '[Yn]', False: '[yN]', None: '[yn]'}[default]
     prompt = f'{prompt.strip()} {examples} '
diff --git a/src/emsarray/cli/command.py b/src/emsarray/cli/command.py
index cec483b0..ef774ad1 100644
--- a/src/emsarray/cli/command.py
+++ b/src/emsarray/cli/command.py
@@ -1,6 +1,5 @@
 import abc
 import argparse
-from typing import Optional
 
 from emsarray.cli import utils
 
@@ -24,11 +23,11 @@ def name(self) -> str:
 
     #: A short description of what this subcommand does,
     #: shown as part of the usage message for the base command.
-    help: Optional[str] = None
+    help: str | None = None
 
     #: A longer description of what this subcommand does,
     #: shown as part of the usage message for this subcommand.
-    description: Optional[str] = None
+    description: str | None = None
 
     def add_parser(self, subparsers: argparse._SubParsersAction) -> None:
         parser = subparsers.add_parser(
diff --git a/src/emsarray/cli/commands/export_geometry.py b/src/emsarray/cli/commands/export_geometry.py
index 4a0a860c..21d9a9c9 100644
--- a/src/emsarray/cli/commands/export_geometry.py
+++ b/src/emsarray/cli/commands/export_geometry.py
@@ -1,7 +1,7 @@
 import argparse
 import logging
+from collections.abc import Callable
 from pathlib import Path
-from typing import Callable
 
 import xarray
 
diff --git a/src/emsarray/cli/commands/plot.py b/src/emsarray/cli/commands/plot.py
index 5266f44c..ec824a8a 100644
--- a/src/emsarray/cli/commands/plot.py
+++ b/src/emsarray/cli/commands/plot.py
@@ -1,8 +1,9 @@
 import argparse
 import functools
 import logging
+from collections.abc import Callable
 from pathlib import Path
-from typing import Any, Callable, Optional, TypeVar
+from typing import Any, TypeVar
 
 import emsarray
 from emsarray.cli import BaseCommand, CommandException
@@ -28,7 +29,7 @@ def __init__(
         dest: str,
         *,
         value_type: Callable = str,
-        default: Optional[dict[str, Any]] = None,
+        default: dict[str, Any] | None = None,
         **kwargs: Any,
     ):
         if default is None:
@@ -42,7 +43,7 @@ def __call__(
         parser: argparse.ArgumentParser,
         namespace: argparse.Namespace,
         values: Any,
-        option_string: Optional[str] = None,
+        option_string: str | None = None,
     ) -> None:
         super().__call__
         holder = getattr(namespace, self.dest, {})
diff --git a/src/emsarray/cli/utils.py b/src/emsarray/cli/utils.py
index 446dcdf8..34c3e285 100644
--- a/src/emsarray/cli/utils.py
+++ b/src/emsarray/cli/utils.py
@@ -9,10 +9,10 @@
 import re
 import sys
 import textwrap
-from collections.abc import Iterator
+from collections.abc import Callable, Iterator
 from functools import wraps
 from pathlib import Path
-from typing import Callable, Optional, Protocol
+from typing import Protocol
 
 from shapely.geometry import box, shape
 from shapely.geometry.base import BaseGeometry
@@ -30,7 +30,7 @@
 class MainCallable(Protocol):
     def __call__(
         self,
-        argv: Optional[list[str]] = None,
+        argv: list[str] | None = None,
         handle_errors: bool = True,
     ) -> None:
         ...
@@ -112,7 +112,7 @@ def decorator(
     ) -> MainCallable:
         @wraps(fn)
         def wrapper(
-            argv: Optional[list[str]] = None,
+            argv: list[str] | None = None,
             handle_errors: bool = True,
         ) -> None:
             parser = argparse.ArgumentParser(
@@ -172,7 +172,7 @@ def nice_console_errors() -> Iterator:
 
 class DoubleNewlineDescriptionFormatter(argparse.HelpFormatter):
     def _fill_text(self, text: str, width: int, indent: str) -> str:
-        fill_text = super(DoubleNewlineDescriptionFormatter, self)._fill_text
+        fill_text = super()._fill_text
 
         return '\n\n'.join(
             fill_text(paragraph, width, indent)
diff --git a/src/emsarray/compat/shapely.py b/src/emsarray/compat/shapely.py
index 1fe8d2c2..d5cf4295 100644
--- a/src/emsarray/compat/shapely.py
+++ b/src/emsarray/compat/shapely.py
@@ -1,6 +1,6 @@
 import warnings
 from collections.abc import Iterable
-from typing import Generic, TypeVar, Union, cast
+from typing import Generic, TypeVar, cast
 
 import numpy
 import shapely
@@ -31,7 +31,7 @@ class SpatialIndex(Generic[T]):
 
     def __init__(
         self,
-        items: Union[numpy.ndarray, Iterable[tuple[BaseGeometry, T]]],
+        items: numpy.ndarray | Iterable[tuple[BaseGeometry, T]],
     ):
         self.items = numpy.array(items, dtype=self.dtype)
 
diff --git a/src/emsarray/conventions/_base.py b/src/emsarray/conventions/_base.py
index a0ba6f82..d43d5eb7 100644
--- a/src/emsarray/conventions/_base.py
+++ b/src/emsarray/conventions/_base.py
@@ -3,11 +3,9 @@
 import enum
 import logging
 import warnings
-from collections.abc import Hashable, Iterable, Sequence
+from collections.abc import Callable, Hashable, Iterable, Sequence
 from functools import cached_property
-from typing import (
-    TYPE_CHECKING, Any, Callable, Generic, Optional, TypeVar, Union, cast
-)
+from typing import TYPE_CHECKING, Any, Generic, TypeVar, cast
 
 import numpy
 import xarray
@@ -166,7 +164,7 @@ def check_validity(cls, dataset: xarray.Dataset) -> None:
 
     @classmethod
     @abc.abstractmethod
-    def check_dataset(cls, dataset: xarray.Dataset) -> Optional[int]:
+    def check_dataset(cls, dataset: xarray.Dataset) -> int | None:
         """
         Check if a dataset uses this convention.
 
@@ -582,7 +580,7 @@ def wind_index(
         self,
         linear_index: int,
         *,
-        grid_kind: Optional[GridKind] = None,
+        grid_kind: GridKind | None = None,
     ) -> Index:
         """Convert a linear index to a conventnion native index.
 
@@ -635,7 +633,7 @@ def wind_index(
     def unravel_index(
         self,
         linear_index: int,
-        grid_kind: Optional[GridKind] = None,
+        grid_kind: GridKind | None = None,
     ) -> Index:
         """An alias for :meth:`Convention.wind_index()`.
 
@@ -772,7 +770,7 @@ def ravel(
         self,
         data_array: xarray.DataArray,
         *,
-        linear_dimension: Optional[Hashable] = None,
+        linear_dimension: Hashable | None = None,
     ) -> xarray.DataArray:
         """
         Flatten the surface dimensions of a :class:`~xarray.DataArray`,
@@ -815,9 +813,9 @@ def wind(
         self,
         data_array: xarray.DataArray,
         *,
-        grid_kind: Optional[GridKind] = None,
-        axis: Optional[int] = None,
-        linear_dimension: Optional[Hashable] = None,
+        grid_kind: GridKind | None = None,
+        axis: int | None = None,
+        linear_dimension: Hashable | None = None,
     ) -> xarray.DataArray:
         """
         Wind a flattened :class:`~xarray.DataArray`
@@ -935,9 +933,9 @@ def data_crs(self) -> 'CRS':
     def plot_on_figure(
         self,
         figure: 'Figure',
-        scalar: Optional[DataArrayOrName] = None,
-        vector: Optional[tuple[DataArrayOrName, DataArrayOrName]] = None,
-        title: Optional[str] = None,
+        scalar: DataArrayOrName | None = None,
+        vector: tuple[DataArrayOrName, DataArrayOrName] | None = None,
+        title: str | None = None,
         **kwargs: Any,
     ) -> None:
         """Plot values for a :class:`~xarray.DataArray`
@@ -1015,10 +1013,10 @@ def plot(self, *args: Any, **kwargs: Any) -> None:
     def animate_on_figure(
         self,
         figure: 'Figure',
-        scalar: Optional[DataArrayOrName] = None,
-        vector: Optional[tuple[DataArrayOrName, DataArrayOrName]] = None,
-        coordinate: Optional[DataArrayOrName] = None,
-        title: Optional[Union[str, Callable[[Any], str]]] = None,
+        scalar: DataArrayOrName | None = None,
+        vector: tuple[DataArrayOrName, DataArrayOrName] | None = None,
+        coordinate: DataArrayOrName | None = None,
+        title: str | Callable[[Any], str] | None = None,
         **kwargs: Any,
     ) -> 'FuncAnimation':
         """
@@ -1115,7 +1113,7 @@ def animate_on_figure(
     @utils.timed_func
     def make_poly_collection(
         self,
-        data_array: Optional[DataArrayOrName] = None,
+        data_array: DataArrayOrName | None = None,
         **kwargs: Any,
     ) -> 'PolyCollection':
         """
@@ -1192,7 +1190,7 @@ def make_poly_collection(
 
     def make_patch_collection(
         self,
-        data_array: Optional[DataArrayOrName] = None,
+        data_array: DataArrayOrName | None = None,
         **kwargs: Any,
     ) -> 'PolyCollection':
         warnings.warn(
@@ -1206,8 +1204,8 @@ def make_patch_collection(
     def make_quiver(
         self,
         axes: 'Axes',
-        u: Optional[DataArrayOrName] = None,
-        v: Optional[DataArrayOrName] = None,
+        u: DataArrayOrName | None = None,
+        v: DataArrayOrName | None = None,
         **kwargs: Any,
     ) -> 'Quiver':
         """
@@ -1238,7 +1236,7 @@ def make_quiver(
         # sometimes preferring to fill them in later,
         # so `u` and `v` are optional.
         # If they are not provided, we set default quiver values of `numpy.nan`.
-        values: Union[tuple[numpy.ndarray, numpy.ndarray], tuple[float, float]]
+        values: tuple[numpy.ndarray, numpy.ndarray] | tuple[float, float]
         values = numpy.nan, numpy.nan
 
         if u is not None and v is not None:
@@ -1331,7 +1329,7 @@ def mask(self) -> numpy.ndarray:
         return cast(numpy.ndarray, mask)
 
     @cached_property
-    def geometry(self) -> Union[Polygon, MultiPolygon]:
+    def geometry(self) -> Polygon | MultiPolygon:
         """
         A :class:`shapely.Polygon` or :class:`shapely.MultiPolygon` that represents
         the geometry of the entire dataset.
@@ -1438,7 +1436,7 @@ def spatial_index(self) -> SpatialIndex[SpatialIndexItem[Index]]:
     def get_index_for_point(
         self,
         point: Point,
-    ) -> Optional[SpatialIndexItem[Index]]:
+    ) -> SpatialIndexItem[Index] | None:
         """
         Find the index for a :class:`~shapely.Point` in the dataset.
 
@@ -1761,8 +1759,8 @@ def ocean_floor(self) -> xarray.Dataset:
     def normalize_depth_variables(
         self,
         *,
-        positive_down: Optional[bool] = None,
-        deep_to_shallow: Optional[bool] = None,
+        positive_down: bool | None = None,
+        deep_to_shallow: bool | None = None,
     ) -> xarray.Dataset:
         """An alias for :func:`emsarray.operations.depth.normalize_depth_variables`"""
         return depth.normalize_depth_variables(
@@ -1895,7 +1893,7 @@ def wind_index(
         self,
         linear_index: int,
         *,
-        grid_kind: Optional[GridKind] = None,
+        grid_kind: GridKind | None = None,
     ) -> Index:
         if grid_kind is None:
             grid_kind = self.default_grid_kind
@@ -1907,7 +1905,7 @@ def ravel(
         self,
         data_array: xarray.DataArray,
         *,
-        linear_dimension: Optional[Hashable] = None,
+        linear_dimension: Hashable | None = None,
     ) -> xarray.DataArray:
         kind = self.get_grid_kind(data_array)
         dimensions = self.grid_dimensions[kind]
@@ -1919,9 +1917,9 @@ def wind(
         self,
         data_array: xarray.DataArray,
         *,
-        grid_kind: Optional[GridKind] = None,
-        axis: Optional[int] = None,
-        linear_dimension: Optional[Hashable] = None,
+        grid_kind: GridKind | None = None,
+        axis: int | None = None,
+        linear_dimension: Hashable | None = None,
     ) -> xarray.DataArray:
         if axis is not None:
             linear_dimension = data_array.dims[axis]
diff --git a/src/emsarray/conventions/_registry.py b/src/emsarray/conventions/_registry.py
index c70d5d14..dfbb65ac 100644
--- a/src/emsarray/conventions/_registry.py
+++ b/src/emsarray/conventions/_registry.py
@@ -1,12 +1,10 @@
 import logging
-import sys
 import warnings
 from collections.abc import Iterable
 from contextlib import suppress
 from functools import cached_property
 from importlib import metadata
 from itertools import chain
-from typing import Optional
 
 import xarray
 
@@ -94,7 +92,7 @@ def match_conventions(self, dataset: xarray.Dataset) -> list[tuple[type[Conventi
                 matches.append((convention, match))
         return sorted(matches, key=lambda m: m[1], reverse=True)
 
-    def guess_convention(self, dataset: xarray.Dataset) -> Optional[type[Convention]]:
+    def guess_convention(self, dataset: xarray.Dataset) -> type[Convention] | None:
         """
         Guess the correct :class:`.Convention` implementation for a dataset.
         """
@@ -109,7 +107,7 @@ def guess_convention(self, dataset: xarray.Dataset) -> Optional[type[Convention]
 registry = ConventionRegistry()
 
 
-def get_dataset_convention(dataset: xarray.Dataset) -> Optional[type[Convention]]:
+def get_dataset_convention(dataset: xarray.Dataset) -> type[Convention] | None:
     """Find the most appropriate Convention subclass for this dataset.
 
     Parameters
@@ -146,10 +144,7 @@ def entry_point_conventions() -> Iterable[type[Convention]]:
         ('emsarray.formats', True),
     ]
     for group, deprecated in groups:
-        if sys.version_info >= (3, 10):
-            entry_points = metadata.entry_points(group=group)
-        else:
-            entry_points = metadata.entry_points().get(group, [])
+        entry_points = metadata.entry_points(group=group)
 
         for entry_point in entry_points:
             if deprecated:
diff --git a/src/emsarray/conventions/arakawa_c.py b/src/emsarray/conventions/arakawa_c.py
index 1ea25d1d..150ed6b0 100644
--- a/src/emsarray/conventions/arakawa_c.py
+++ b/src/emsarray/conventions/arakawa_c.py
@@ -10,7 +10,7 @@
 import logging
 from collections.abc import Hashable, Sequence
 from functools import cached_property
-from typing import Optional, cast
+from typing import cast
 
 import numpy
 import xarray
@@ -168,7 +168,7 @@ def __init__(
         self,
         dataset: xarray.Dataset,
         *,
-        coordinate_names: Optional[dict[Hashable, tuple[Hashable, Hashable]]] = None,
+        coordinate_names: dict[Hashable, tuple[Hashable, Hashable]] | None = None,
     ):
         super().__init__(dataset)
 
@@ -192,7 +192,7 @@ def __init__(
             )
 
     @classmethod
-    def check_dataset(cls, dataset: xarray.Dataset) -> Optional[int]:
+    def check_dataset(cls, dataset: xarray.Dataset) -> int | None:
         if not hasattr(cls, 'coordinate_names'):
             return None
 
@@ -330,7 +330,7 @@ def apply_clip_mask(self, clip_mask: xarray.Dataset, work_dir: Pathish) -> xarra
 def c_mask_from_centres(
     face_mask: numpy.ndarray,
     dimensions: ArakawaCDimensions,
-    coords: Optional[DatasetCoordinates] = None,
+    coords: DatasetCoordinates | None = None,
 ) -> xarray.Dataset:
     """
     Create a mask for a SHOC standard file given a mask array for the cell
diff --git a/src/emsarray/conventions/grid.py b/src/emsarray/conventions/grid.py
index ae0b278e..d45fd231 100644
--- a/src/emsarray/conventions/grid.py
+++ b/src/emsarray/conventions/grid.py
@@ -9,7 +9,7 @@
 from collections.abc import Hashable, Sequence
 from contextlib import suppress
 from functools import cached_property
-from typing import Generic, Optional, TypeVar, cast
+from typing import Generic, TypeVar, cast
 
 import numpy
 import xarray
@@ -51,8 +51,8 @@ class CFGridTopology(abc.ABC):
     def __init__(
         self,
         dataset: xarray.Dataset,
-        longitude: Optional[Hashable] = None,
-        latitude: Optional[Hashable] = None,
+        longitude: Hashable | None = None,
+        latitude: Hashable | None = None,
     ):
         """
         Construct a new :class:`CFGridTopology` instance for a dataset.
@@ -200,9 +200,9 @@ def __init__(
         self,
         dataset: xarray.Dataset,
         *,
-        latitude: Optional[Hashable] = None,
-        longitude: Optional[Hashable] = None,
-        topology: Optional[Topology] = None,
+        latitude: Hashable | None = None,
+        longitude: Hashable | None = None,
+        topology: Topology | None = None,
     ) -> None:
         """
         Construct a new :class:`CFGrid` instance.
@@ -270,7 +270,7 @@ def get_all_geometry_names(self) -> list[Hashable]:
             self.topology.latitude_name,
         ]
 
-        bounds_names: list[Optional[Hashable]] = [
+        bounds_names: list[Hashable | None] = [
             self.topology.longitude.attrs.get('bounds', None),
             self.topology.latitude.attrs.get('bounds', None),
         ]
@@ -387,7 +387,7 @@ class CFGrid1D(CFGrid[CFGrid1DTopology]):
     topology_class = CFGrid1DTopology
 
     @classmethod
-    def check_dataset(cls, dataset: xarray.Dataset) -> Optional[int]:
+    def check_dataset(cls, dataset: xarray.Dataset) -> int | None:
         """
         A dataset is a 1D CF grid if it has one dimensional
         latitude and longitude coordinate variables.
@@ -543,7 +543,7 @@ class CFGrid2D(CFGrid[CFGrid2DTopology]):
     topology_class = CFGrid2DTopology
 
     @classmethod
-    def check_dataset(cls, dataset: xarray.Dataset) -> Optional[int]:
+    def check_dataset(cls, dataset: xarray.Dataset) -> int | None:
         """
         A dataset is a 2D CF grid if it has two dimensional
         latitude and longitude coordinate variables.
diff --git a/src/emsarray/conventions/shoc.py b/src/emsarray/conventions/shoc.py
index 1483499e..cb205711 100644
--- a/src/emsarray/conventions/shoc.py
+++ b/src/emsarray/conventions/shoc.py
@@ -17,7 +17,6 @@
 import logging
 from collections.abc import Hashable
 from functools import cached_property
-from typing import Optional
 
 import xarray
 
@@ -108,7 +107,7 @@ def topology(self) -> CFGrid2DTopology:
         return CFGrid2DTopology(self.dataset, latitude=latitude, longitude=longitude)
 
     @classmethod
-    def check_dataset(cls, dataset: xarray.Dataset) -> Optional[int]:
+    def check_dataset(cls, dataset: xarray.Dataset) -> int | None:
         if 'ems_version' not in dataset.attrs:
             return None
         if not set(dataset.dims).issuperset(cls._dimensions):
diff --git a/src/emsarray/conventions/ugrid.py b/src/emsarray/conventions/ugrid.py
index a81fb631..0d74bd4b 100644
--- a/src/emsarray/conventions/ugrid.py
+++ b/src/emsarray/conventions/ugrid.py
@@ -14,7 +14,7 @@
 from contextlib import suppress
 from dataclasses import dataclass
 from functools import cached_property
-from typing import Any, Optional, cast
+from typing import Any, cast
 
 import numpy
 import shapely
@@ -353,7 +353,7 @@ class Mesh2DTopology:
     #: The name of the mesh topology variable. Optional. If not provided, the
     #: mesh topology dummy variable will be found by checking the ``cf_role``
     #: attribute.
-    topology_key: Optional[Hashable] = None
+    topology_key: Hashable | None = None
 
     #: The default dtype to use for index data arrays. Hard coded to ``int32``,
     #: which should be sufficient for all datasets. ``int16`` is too small for
@@ -444,7 +444,7 @@ def node_y(self) -> xarray.DataArray:
         return self.dataset.data_vars[self._node_coordinates[1]]
 
     @property
-    def edge_x(self) -> Optional[xarray.DataArray]:
+    def edge_x(self) -> xarray.DataArray | None:
         """Data array of characteristic edge X / longitude coordinates. Optional."""
         try:
             return self.dataset.data_vars[self._edge_coordinates[0]]
@@ -452,7 +452,7 @@ def edge_x(self) -> Optional[xarray.DataArray]:
             return None
 
     @property
-    def edge_y(self) -> Optional[xarray.DataArray]:
+    def edge_y(self) -> xarray.DataArray | None:
         """Data array of characteristic edge y / latitude coordinates. Optional."""
         try:
             return self.dataset.data_vars[self._edge_coordinates[1]]
@@ -460,7 +460,7 @@ def edge_y(self) -> Optional[xarray.DataArray]:
             return None
 
     @property
-    def face_x(self) -> Optional[xarray.DataArray]:
+    def face_x(self) -> xarray.DataArray | None:
         """Data array of characteristic face x / longitude coordinates. Optional."""
         try:
             return self.dataset.data_vars[self._face_coordinates[0]]
@@ -468,7 +468,7 @@ def face_x(self) -> Optional[xarray.DataArray]:
             return None
 
     @property
-    def face_y(self) -> Optional[xarray.DataArray]:
+    def face_y(self) -> xarray.DataArray | None:
         """Data array of characteristic face y / latitude coordinates. Optional."""
         try:
             return self.dataset.data_vars[self._face_coordinates[1]]
@@ -1024,7 +1024,7 @@ class UGrid(DimensionConvention[UGridKind, UGridIndex]):
     default_grid_kind = UGridKind.face
 
     @classmethod
-    def check_dataset(cls, dataset: xarray.Dataset) -> Optional[int]:
+    def check_dataset(cls, dataset: xarray.Dataset) -> int | None:
         """
         A UGrid dataset needs a global attribute of Conventions = 'UGRID/...',
         and a variable with attribute cf_role = 'mesh_topology'
diff --git a/src/emsarray/formats.py b/src/emsarray/formats.py
index 0b2bb8a4..e5efd92d 100644
--- a/src/emsarray/formats.py
+++ b/src/emsarray/formats.py
@@ -1,6 +1,6 @@
 import warnings
 from functools import wraps
-from typing import Any, Optional
+from typing import Any
 
 import xarray
 
@@ -17,7 +17,7 @@ def _warn_old_new(old: str, new: str, **kwargs: Any) -> None:
 
 
 @wraps(get_dataset_convention)
-def get_file_format(dataset: xarray.Dataset, **kwargs: Any) -> Optional[type[Convention]]:
+def get_file_format(dataset: xarray.Dataset, **kwargs: Any) -> type[Convention] | None:
     _warn_old_new(
         old="emsarray.formats.get_file_format",
         new="emsarray.conventions.get_dataset_convention",
diff --git a/src/emsarray/nco.py b/src/emsarray/nco.py
index 04c5ca56..3f767ed7 100644
--- a/src/emsarray/nco.py
+++ b/src/emsarray/nco.py
@@ -11,9 +11,9 @@
 import subprocess
 from collections.abc import Sequence
 from pathlib import Path
-from typing import Any, Optional, Union
+from typing import Any
 
-Pathish = Union[Path, str]
+from emsarray.types import Pathish
 
 
 def _check_call(cmd: Sequence[str], stdin: Any = subprocess.DEVNULL, **kwargs: Any) -> None:
@@ -23,7 +23,7 @@ def _check_call(cmd: Sequence[str], stdin: Any = subprocess.DEVNULL, **kwargs: A
 def ncrcat(
     input_files: Sequence[Pathish],
     output_file: Pathish,
-    flags: Optional[str] = None,
+    flags: str | None = None,
     history: bool = False,
 ) -> None:
     """Concatenates a set of netCDF files together using `ncrcat`."""
diff --git a/src/emsarray/operations/depth.py b/src/emsarray/operations/depth.py
index 3ab97651..4473cf3f 100644
--- a/src/emsarray/operations/depth.py
+++ b/src/emsarray/operations/depth.py
@@ -4,8 +4,8 @@
 """
 import warnings
 from collections import defaultdict
-from collections.abc import Hashable
-from typing import Iterable, Optional, cast
+from collections.abc import Hashable, Iterable
+from typing import cast
 
 import numpy
 import xarray
@@ -18,7 +18,7 @@ def ocean_floor(
     dataset: xarray.Dataset,
     depth_coordinates: Iterable[DataArrayOrName],
     *,
-    non_spatial_variables: Optional[Iterable[DataArrayOrName]] = None,
+    non_spatial_variables: Iterable[DataArrayOrName] | None = None,
 ) -> xarray.Dataset:
     """Make a new :class:`xarray.Dataset` reduced along the given depth
     coordinates to only contain values along the ocean floor.
@@ -200,8 +200,8 @@ def normalize_depth_variables(
     dataset: xarray.Dataset,
     depth_coordinates: Iterable[DataArrayOrName],
     *,
-    positive_down: Optional[bool] = None,
-    deep_to_shallow: Optional[bool] = None,
+    positive_down: bool | None = None,
+    deep_to_shallow: bool | None = None,
 ) -> xarray.Dataset:
     """
     Some datasets represent depth as a positive variable, some as negative.
diff --git a/src/emsarray/operations/geometry.py b/src/emsarray/operations/geometry.py
index 1034646a..2ef472dd 100644
--- a/src/emsarray/operations/geometry.py
+++ b/src/emsarray/operations/geometry.py
@@ -7,7 +7,7 @@
 import pathlib
 from collections.abc import Generator, Iterable, Iterator
 from contextlib import contextmanager
-from typing import IO, Any, Optional, TypeVar, Union
+from typing import IO, Any, TypeVar
 
 import geojson
 import shapefile
@@ -108,7 +108,7 @@ def write_geojson(
 
 
 @contextmanager
-def _maybe_open(path_or_file: Union[Pathish, IO], mode: str) -> Generator[IO, None, None]:
+def _maybe_open(path_or_file: Pathish | IO, mode: str) -> Generator[IO, None, None]:
     """
     Given either a path to a file or an open file handle,
     return an open file handle wrapped in a context manager.
@@ -128,12 +128,12 @@ def _maybe_open(path_or_file: Union[Pathish, IO], mode: str) -> Generator[IO, No
 
 def write_shapefile(
     dataset: xarray.Dataset,
-    target: Optional[Pathish] = None,
+    target: Pathish | None = None,
     *,
-    shp: Optional[Union[Pathish, IO]] = None,
-    shx: Optional[Union[Pathish, IO]] = None,
-    dbf: Optional[Union[Pathish, IO]] = None,
-    prj: Optional[Union[Pathish, IO]] = None,
+    shp: Pathish | IO | None = None,
+    shx: Pathish | IO | None = None,
+    dbf: Pathish | IO | None = None,
+    prj: Pathish | IO | None = None,
     **kwargs: Any,
 ) -> None:
     """
diff --git a/src/emsarray/plot.py b/src/emsarray/plot.py
index 6cac2b28..348658d1 100644
--- a/src/emsarray/plot.py
+++ b/src/emsarray/plot.py
@@ -1,6 +1,6 @@
 import importlib.metadata
-from collections.abc import Iterable
-from typing import Any, Callable, Literal, Optional, Union
+from collections.abc import Callable, Iterable
+from typing import Any, Literal
 
 import numpy
 import packaging.version
@@ -224,7 +224,7 @@ def polygons_to_collection(
 def make_plot_title(
     dataset: xarray.Dataset,
     data_array: xarray.DataArray,
-) -> Optional[str]:
+) -> str | None:
     """
     Make a suitable plot title for a variable.
     This will attempt to find a name for the variable by looking through the attributes.
@@ -268,11 +268,11 @@ def plot_on_figure(
     figure: Figure,
     convention: 'conventions.Convention',
     *,
-    scalar: Optional[xarray.DataArray] = None,
-    vector: Optional[tuple[xarray.DataArray, xarray.DataArray]] = None,
-    title: Optional[str] = None,
-    projection: Optional[cartopy.crs.Projection] = None,
-    landmarks: Optional[Iterable[Landmark]] = None,
+    scalar: xarray.DataArray | None = None,
+    vector: tuple[xarray.DataArray, xarray.DataArray] | None = None,
+    title: str | None = None,
+    projection: cartopy.crs.Projection | None = None,
+    landmarks: Iterable[Landmark] | None = None,
     gridlines: bool = True,
     coast: bool = True,
 ) -> None:
@@ -360,15 +360,15 @@ def animate_on_figure(
     convention: 'conventions.Convention',
     *,
     coordinate: xarray.DataArray,
-    scalar: Optional[xarray.DataArray] = None,
-    vector: Optional[tuple[xarray.DataArray, xarray.DataArray]] = None,
-    title: Optional[Union[str, Callable[[Any], str]]] = None,
-    projection: Optional[cartopy.crs.Projection] = None,
-    landmarks: Optional[Iterable[Landmark]] = None,
+    scalar: xarray.DataArray | None = None,
+    vector: tuple[xarray.DataArray, xarray.DataArray] | None = None,
+    title: str | Callable[[Any], str] | None = None,
+    projection: cartopy.crs.Projection | None = None,
+    landmarks: Iterable[Landmark] | None = None,
     gridlines: bool = True,
     coast: bool = True,
     interval: int = 1000,
-    repeat: Union[bool, Literal['cycle', 'bounce']] = True,
+    repeat: bool | Literal['cycle', 'bounce'] = True,
 ) -> animation.FuncAnimation:
     """
     Plot a :class:`xarray.DataArray`
diff --git a/src/emsarray/transect.py b/src/emsarray/transect.py
index e3d92fee..9bba29b9 100644
--- a/src/emsarray/transect.py
+++ b/src/emsarray/transect.py
@@ -1,7 +1,7 @@
 import dataclasses
-from collections.abc import Iterable
+from collections.abc import Callable, Iterable
 from functools import cached_property
-from typing import Any, Callable, Generic, Optional, Union, cast
+from typing import Any, Generic, cast
 
 import cfunits
 import numpy
@@ -117,7 +117,7 @@ def __init__(
         self,
         dataset: xarray.Dataset,
         line: shapely.LineString,
-        depth: Optional[DataArrayOrName] = None,
+        depth: DataArrayOrName | None = None,
     ):
         self.dataset = dataset
         self.convention = dataset.ems
@@ -223,7 +223,7 @@ def transect_dataset(self) -> xarray.Dataset:
 
     def _set_up_axis(self, variable: xarray.DataArray) -> tuple[str, Formatter]:
         title = str(variable.attrs.get('long_name'))
-        units: Optional[str] = variable.attrs.get('units')
+        units: str | None = variable.attrs.get('units')
 
         if units is not None:
             # Use cfunits to normalize the units to their short symbol form.
@@ -237,7 +237,7 @@ def _set_up_axis(self, variable: xarray.DataArray) -> tuple[str, Formatter]:
     def _crs_for_point(
         self,
         point: shapely.Point,
-        globe: Optional[crs.Globe] = None,
+        globe: crs.Globe | None = None,
     ) -> crs.Projection:
         return crs.AzimuthalEquidistant(
             central_longitude=point.x, central_latitude=point.y, globe=globe)
@@ -557,13 +557,13 @@ def plot_on_figure(
         figure: Figure,
         data_array: xarray.DataArray,
         *,
-        title: Optional[str] = None,
+        title: str | None = None,
         trim_nans: bool = True,
         clamp_to_surface: bool = True,
-        bathymetry: Optional[xarray.DataArray] = None,
-        cmap: Union[str, Colormap] = 'jet',
+        bathymetry: xarray.DataArray | None = None,
+        cmap: str | Colormap = 'jet',
         ocean_floor_colour: str = 'black',
-        landmarks: Optional[list[Landmark]] = None,
+        landmarks: list[Landmark] | None = None,
     ) -> None:
         """
         Plot the data array along this transect.
@@ -617,14 +617,14 @@ def animate_on_figure(
         figure: Figure,
         data_array: xarray.DataArray,
         *,
-        title: Optional[Union[str, Callable[[Any], str]]] = None,
+        title: str | Callable[[Any], str] | None = None,
         trim_nans: bool = True,
         clamp_to_surface: bool = True,
-        bathymetry: Optional[xarray.DataArray] = None,
-        cmap: Union[str, Colormap] = 'jet',
+        bathymetry: xarray.DataArray | None = None,
+        cmap: str | Colormap = 'jet',
         ocean_floor_colour: str = 'black',
-        landmarks: Optional[list[Landmark]] = None,
-        coordinate: Optional[xarray.DataArray] = None,
+        landmarks: list[Landmark] | None = None,
+        coordinate: xarray.DataArray | None = None,
         interval: int = 200,
     ) -> animation.FuncAnimation:
         """
@@ -706,13 +706,13 @@ def _plot_on_figure(
         figure: Figure,
         data_array: xarray.DataArray,
         *,
-        title: Optional[str] = None,
+        title: str | None = None,
         trim_nans: bool = True,
         clamp_to_surface: bool = True,
-        bathymetry: Optional[xarray.DataArray] = None,
-        cmap: Union[str, Colormap] = 'jet',
+        bathymetry: xarray.DataArray | None = None,
+        cmap: str | Colormap = 'jet',
         ocean_floor_colour: str = 'black',
-        landmarks: Optional[list[Landmark]] = None,
+        landmarks: list[Landmark] | None = None,
     ) -> tuple[Axes, PolyCollection, xarray.DataArray]:
         """
         Construct the axes and PolyCollections on a plot,
diff --git a/src/emsarray/utils.py b/src/emsarray/utils.py
index 63fa15fa..12c05a1b 100644
--- a/src/emsarray/utils.py
+++ b/src/emsarray/utils.py
@@ -15,10 +15,10 @@
 import time
 import warnings
 from collections.abc import (
-    Hashable, Iterable, Mapping, MutableMapping, Sequence
+    Callable, Hashable, Iterable, Mapping, MutableMapping, Sequence
 )
 from types import TracebackType
-from typing import Any, Callable, Literal, Optional, TypeVar, Union, cast
+from typing import Any, Literal, TypeVar, cast
 
 import cftime
 import netCDF4
@@ -58,10 +58,10 @@ def __enter__(self) -> 'PerfTimer':
 
     def __exit__(
         self,
-        exc_type: Optional[type[_Exception]],
-        exc_value: Optional[_Exception],
+        exc_type: type[_Exception] | None,
+        exc_value: _Exception | None,
         traceback: TracebackType
-    ) -> Optional[bool]:
+    ) -> bool | None:
         self._stop = time.perf_counter()
         self.running = False
         return None
@@ -113,7 +113,7 @@ def wrapper(*args: Any, **kwargs: Any) -> _T:
 def to_netcdf_with_fixes(
     dataset: xarray.Dataset,
     path: Pathish,
-    time_variable: Optional[DataArrayOrName] = None,
+    time_variable: DataArrayOrName | None = None,
     **kwargs: Any,
 ) -> None:
     """Saves a :class:`xarray.Dataset` to a netCDF4 file,
@@ -151,7 +151,7 @@ def to_netcdf_with_fixes(
         fix_time_units_for_ems(path, data_array_to_name(dataset, time_variable))
 
 
-def format_time_units_for_ems(units: str, calendar: Optional[str] = DEFAULT_CALENDAR) -> str:
+def format_time_units_for_ems(units: str, calendar: str | None = DEFAULT_CALENDAR) -> str:
     """
     Reformat a given time unit string to an EMS-compatible string. ``xarray``
     will always format time unit strings using ISO8601 strings with
@@ -238,14 +238,14 @@ def fix_time_units_for_ems(
         dataset.sync()
 
 
-def _get_variables(dataset_or_array: Union[xarray.Dataset, xarray.DataArray]) -> list[xarray.Variable]:
+def _get_variables(dataset_or_array: xarray.Dataset | xarray.DataArray) -> list[xarray.Variable]:
     if isinstance(dataset_or_array, xarray.Dataset):
         return list(dataset_or_array.variables.values())
     else:
         return [dataset_or_array.variable]
 
 
-def disable_default_fill_value(dataset_or_array: Union[xarray.Dataset, xarray.DataArray]) -> None:
+def disable_default_fill_value(dataset_or_array: xarray.Dataset | xarray.DataArray) -> None:
     """
     Update all variables on this dataset or data array and disable the
     automatic ``_FillValue`` :mod:`xarray` sets. An automatic fill value can spoil
@@ -428,7 +428,7 @@ def check_data_array_dimensions_match(
     dataset: xarray.Dataset,
     data_array: xarray.DataArray,
     *,
-    dimensions: Optional[Sequence[Hashable]] = None,
+    dimensions: Sequence[Hashable] | None = None,
 ) -> None:
     """
     Check that the dimensions of a :class:`xarray.DataArray`
@@ -522,7 +522,7 @@ def move_dimensions_to_end(
 def ravel_dimensions(
     data_array: xarray.DataArray,
     dimensions: list[Hashable],
-    linear_dimension: Optional[Hashable] = None,
+    linear_dimension: Hashable | None = None,
 ) -> xarray.DataArray:
     """
     Flatten the given dimensions of a :class:`~xarray.DataArray`.
@@ -688,7 +688,7 @@ def __init__(self, extra: str) -> None:
 
 def requires_extra(
     extra: str,
-    import_error: Optional[ImportError],
+    import_error: ImportError | None,
     exception_class: type[RequiresExtraException] = RequiresExtraException,
 ) -> Callable[[_T], _T]:
     if import_error is None:
@@ -705,7 +705,7 @@ def error(*args: Any, **kwargs: Any) -> Any:
 def make_polygons_with_holes(
     points: numpy.ndarray,
     *,
-    out: Optional[numpy.ndarray] = None,
+    out: numpy.ndarray | None = None,
 ) -> numpy.ndarray:
     """
     Make a :class:`numpy.ndarray` of :class:`shapely.Polygon` from an array of (n, m, 2) points.
diff --git a/tests/conventions/test_base.py b/tests/conventions/test_base.py
index 43b908e0..489cb4a5 100644
--- a/tests/conventions/test_base.py
+++ b/tests/conventions/test_base.py
@@ -3,7 +3,6 @@
 import pathlib
 from collections.abc import Hashable
 from functools import cached_property
-from typing import Optional
 
 import numpy
 import pandas
@@ -40,7 +39,7 @@ class SimpleConvention(Convention[SimpleGridKind, SimpleGridIndex]):
     default_grid_kind = SimpleGridKind.face
 
     @classmethod
-    def check_dataset(cls, dataset: xarray.Dataset) -> Optional[int]:
+    def check_dataset(cls, dataset: xarray.Dataset) -> int | None:
         return None
 
     @cached_property
@@ -64,7 +63,7 @@ def wind_index(
         self,
         index: int,
         *,
-        grid_kind: Optional[SimpleGridKind] = None,
+        grid_kind: SimpleGridKind | None = None,
     ) -> SimpleGridIndex:
         y, x = map(int, numpy.unravel_index(index, self.shape))
         return SimpleGridIndex(y, x)
@@ -79,7 +78,7 @@ def ravel(
         self,
         data_array: xarray.DataArray,
         *,
-        linear_dimension: Optional[Hashable] = None,
+        linear_dimension: Hashable | None = None,
     ) -> xarray.DataArray:
         self.get_grid_kind(data_array)
         return utils.ravel_dimensions(
@@ -90,9 +89,9 @@ def wind(
         self,
         data_array: xarray.DataArray,
         *,
-        grid_kind: Optional[SimpleGridKind] = None,
-        axis: Optional[int] = None,
-        linear_dimension: Optional[Hashable] = None,
+        grid_kind: SimpleGridKind | None = None,
+        axis: int | None = None,
+        linear_dimension: Hashable | None = None,
     ) -> xarray.DataArray:
         if axis is not None:
             linear_dimension = data_array.dims[axis]
@@ -312,9 +311,9 @@ def test_strtree():
     convention = SimpleConvention(dataset)
 
     line = LineString([(-1, -1), (1.5, 1.5), (1.5, 2.5), (3.9, 3.9)])
-    expected_intersections = set(convention.ravel_index(index) for index in [
+    expected_intersections = {convention.ravel_index(index) for index in [
         SimpleGridIndex(1, 1), SimpleGridIndex(2, 1), SimpleGridIndex(2, 2),
-        SimpleGridIndex(3, 2), SimpleGridIndex(3, 3)])
+        SimpleGridIndex(3, 2), SimpleGridIndex(3, 3)]}
 
     # Query the spatial index
     items = convention.strtree.query(line, predicate='intersects')
diff --git a/tests/conventions/test_registry.py b/tests/conventions/test_registry.py
index cd6be356..8b61196d 100644
--- a/tests/conventions/test_registry.py
+++ b/tests/conventions/test_registry.py
@@ -1,7 +1,6 @@
 """
 Test convention class registration by entry points or manual registration.
 """
-import sys
 from importlib import metadata
 
 import pytest
@@ -70,12 +69,8 @@ def monkeypatch_entrypoint(
         ] for group, entries in entry_points.items()
     }
 
-    if sys.version_info >= (3, 10):
-        def mocked(group: str) -> list[metadata.EntryPoint]:
-            return _entry_points.get(group, [])
-    else:
-        def mocked() -> list[metadata.EntryPoint]:
-            return _entry_points
+    def mocked(group: str) -> list[metadata.EntryPoint]:
+        return _entry_points.get(group, [])
 
     monkeypatch.setattr(metadata, 'entry_points', mocked)
     return entry_points
diff --git a/tests/datasets/make_examples.py b/tests/datasets/make_examples.py
index d427bf3f..e415888d 100644
--- a/tests/datasets/make_examples.py
+++ b/tests/datasets/make_examples.py
@@ -7,7 +7,7 @@
 import datetime
 import functools
 import pathlib
-from typing import Callable
+from collections.abc import Callable
 
 import netCDF4
 import numpy
@@ -186,12 +186,12 @@ def make_ugrid_mesh2d(out: pathlib.Path) -> None:
     faces = [polygon.intersection(envelope) for polygon in voronoi.geoms]
 
     # Get the unique vertices of the faces
-    nodes = numpy.array(list(set(
+    nodes = numpy.array(list({
         p for polygon in faces
         for p in polygon.exterior.coords
-    )))
+    }))
     # A map between {point: index}
-    node_indices = dict((tuple(p), i) for i, p in enumerate(nodes))
+    node_indices = {tuple(p): i for i, p in enumerate(nodes)}
     # Number of vertices
     nnodes = len(node_indices)
     # Maximum vertex count for any face
diff --git a/tests/operations/depth/test_normalize_depth_variables.py b/tests/operations/depth/test_normalize_depth_variables.py
index f415e095..1f7b6828 100644
--- a/tests/operations/depth/test_normalize_depth_variables.py
+++ b/tests/operations/depth/test_normalize_depth_variables.py
@@ -1,5 +1,3 @@
-from typing import Optional
-
 import numpy
 import pytest
 import xarray
@@ -35,8 +33,8 @@ def test_normalize_depth_variable(
     input_positive: str,
     input_deep_to_shallow: bool,
     set_positive: bool,
-    positive_down: Optional[bool],
-    deep_to_shallow: Optional[bool],
+    positive_down: bool | None,
+    deep_to_shallow: bool | None,
     recwarn,
 ):
     # Some datasets have a coordinate with the same dimension name
diff --git a/tests/utils.py b/tests/utils.py
index fd1083b2..23b92ed5 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -5,7 +5,7 @@
 import warnings
 from collections.abc import Hashable
 from functools import cached_property
-from typing import Any, Optional
+from typing import Any
 
 import numpy
 import pytest
@@ -42,7 +42,7 @@ def box(minx, miny, maxx, maxy) -> shapely.Polygon:
     ])
 
 
-def reduce_axes(arr: numpy.ndarray, axes: Optional[tuple[bool, ...]] = None) -> numpy.ndarray:
+def reduce_axes(arr: numpy.ndarray, axes: tuple[bool, ...] | None = None) -> numpy.ndarray:
     """
     Reduce the size of an array by one on an axis-by-axis basis. If an axis is
     reduced, neigbouring values are averaged together
@@ -138,7 +138,7 @@ def __init__(
         self, *,
         j: int,
         i: int,
-        face_mask: Optional[numpy.ndarray] = None,
+        face_mask: numpy.ndarray | None = None,
         include_bounds: bool = False,
     ):
         self.j_size = j