diff --git a/.azure-pipelines.yml b/.azure-pipelines.yml
index 8ae68378d..7e875a4b8 100644
--- a/.azure-pipelines.yml
+++ b/.azure-pipelines.yml
@@ -16,8 +16,8 @@ jobs:
         Python3.11:
           python.version: "3.11"
           RUN_COVERAGE: yes
-        Python3.8:
-          python.version: "3.8"
+        Python3.9:
+          python.version: "3.9"
         PreRelease:
           python.version: "3.11"
           PRERELEASE_DEPENDENCIES: yes
diff --git a/anndata/__init__.py b/anndata/__init__.py
index 9c26702d2..6dd2e2192 100644
--- a/anndata/__init__.py
+++ b/anndata/__init__.py
@@ -1,4 +1,5 @@
 """Annotated multivariate observation data."""
+from __future__ import annotations
 
 try:  # See https://github.com/maresb/hatch-vcs-footgun-example
     from setuptools_scm import get_version
@@ -34,12 +35,14 @@
     read_zarr,
 )
 from ._warnings import (
+    ExperimentalFeatureWarning,
+    ImplicitModificationWarning,
     OldFormatWarning,
     WriteWarning,
-    ImplicitModificationWarning,
-    ExperimentalFeatureWarning,
 )
-from . import experimental
+
+# Experimental needs to be imported last
+from . import experimental  # isort: skip
 
 
 def read(*args, **kwargs):
diff --git a/anndata/_core/access.py b/anndata/_core/access.py
index 7dacaa6dc..7447103d9 100644
--- a/anndata/_core/access.py
+++ b/anndata/_core/access.py
@@ -1,13 +1,16 @@
+from __future__ import annotations
+
 from functools import reduce
-from typing import NamedTuple, Tuple
+from typing import TYPE_CHECKING, NamedTuple
 
-from . import anndata
+if TYPE_CHECKING:
+    from anndata import AnnData
 
 
 class ElementRef(NamedTuple):
-    parent: "anndata.AnnData"
+    parent: AnnData
     attrname: str
-    keys: Tuple[str, ...] = ()
+    keys: tuple[str, ...] = ()
 
     def __str__(self) -> str:
         return f".{self.attrname}" + "".join(map(lambda x: f"['{x}']", self.keys))
diff --git a/anndata/_core/aligned_mapping.py b/anndata/_core/aligned_mapping.py
index 156146518..a69730e26 100644
--- a/anndata/_core/aligned_mapping.py
+++ b/anndata/_core/aligned_mapping.py
@@ -1,26 +1,36 @@
+from __future__ import annotations
+
+import warnings
 from abc import ABC, abstractmethod
 from collections import abc as cabc
+from collections.abc import Iterator, Mapping, Sequence
 from copy import copy
-from typing import Union, Optional, Type, ClassVar, TypeVar  # Special types
-from typing import Iterator, Mapping, Sequence  # ABCs
-from typing import Tuple, List, Dict  # Generic base types
-import warnings
+from typing import (
+    TYPE_CHECKING,
+    ClassVar,
+    TypeVar,
+    Union,
+)
 
 import numpy as np
 import pandas as pd
 from scipy.sparse import spmatrix
 
-from ..utils import deprecated, ensure_df_homogeneous, dim_len
-from . import raw, anndata
-from .views import as_view, view_update
+from anndata._warnings import ExperimentalFeatureWarning, ImplicitModificationWarning
+from anndata.compat import AwkArray
+
+from ..utils import deprecated, dim_len, ensure_df_homogeneous
 from .access import ElementRef
 from .index import _subset
-from anndata.compat import AwkArray
-from anndata._warnings import ExperimentalFeatureWarning, ImplicitModificationWarning
+from .views import as_view, view_update
+
+if TYPE_CHECKING:
+    from .anndata import AnnData
+    from .raw import Raw
 
 
 OneDIdx = Union[Sequence[int], Sequence[bool], slice]
-TwoDIdx = Tuple[OneDIdx, OneDIdx]
+TwoDIdx = tuple[OneDIdx, OneDIdx]
 
 I = TypeVar("I", OneDIdx, TwoDIdx, covariant=True)
 # TODO: pd.DataFrame only allowed in AxisArrays?
@@ -36,16 +46,16 @@ class AlignedMapping(cabc.MutableMapping, ABC):
     _allow_df: ClassVar[bool]
     """If this mapping supports heterogeneous DataFrames"""
 
-    _view_class: ClassVar[Type["AlignedViewMixin"]]
+    _view_class: ClassVar[type[AlignedViewMixin]]
     """The view class for this aligned mapping."""
 
-    _actual_class: ClassVar[Type["AlignedActualMixin"]]
+    _actual_class: ClassVar[type[AlignedActualMixin]]
     """The actual class (which has it’s own data) for this aligned mapping."""
 
     def __repr__(self):
         return f"{type(self).__name__} with keys: {', '.join(self.keys())}"
 
-    def _ipython_key_completions_(self) -> List[str]:
+    def _ipython_key_completions_(self) -> list[str]:
         return list(self.keys())
 
     def _validate_value(self, val: V, key: str) -> V:
@@ -94,7 +104,7 @@ def attrname(self) -> str:
 
     @property
     @abstractmethod
-    def axes(self) -> Tuple[int, ...]:
+    def axes(self) -> tuple[int, ...]:
         """Which axes of the parent is this aligned to?"""
         pass
 
@@ -104,7 +114,7 @@ def is_view(self) -> bool:
         pass
 
     @property
-    def parent(self) -> Union["anndata.AnnData", "raw.Raw"]:
+    def parent(self) -> AnnData | Raw:
         return self._parent
 
     def copy(self):
@@ -117,7 +127,7 @@ def copy(self):
                 d[k] = v.copy()
         return d
 
-    def _view(self, parent: "anndata.AnnData", subset_idx: I):
+    def _view(self, parent: AnnData, subset_idx: I):
         """Returns a subset copy-on-write view of the object."""
         return self._view_class(self, parent, subset_idx)
 
@@ -127,7 +137,7 @@ def as_dict(self) -> dict:
 
 
 class AlignedViewMixin:
-    parent: "anndata.AnnData"
+    parent: AnnData
     """Reference to parent AnnData view"""
 
     attrname: str
@@ -177,7 +187,7 @@ def __len__(self) -> int:
 
 
 class AlignedActualMixin:
-    _data: Dict[str, V]
+    _data: dict[str, V]
     """Underlying mapping to the data"""
 
     is_view = False
@@ -216,7 +226,7 @@ def attrname(self) -> str:
         return f"{self.dim}m"
 
     @property
-    def axes(self) -> Tuple[int]:
+    def axes(self) -> tuple[int]:
         """Axes of the parent this is aligned to"""
         return (self._axis,)
 
@@ -225,7 +235,7 @@ def dim(self) -> str:
         """Name of the dimension this aligned to."""
         return self._dimnames[self._axis]
 
-    def flipped(self) -> "AxisArraysBase":
+    def flipped(self) -> AxisArraysBase:
         """Transpose."""
         new = self.copy()
         new.dimension = abs(self._axis - 1)
@@ -265,9 +275,9 @@ def dim_names(self) -> pd.Index:
 class AxisArrays(AlignedActualMixin, AxisArraysBase):
     def __init__(
         self,
-        parent: Union["anndata.AnnData", "raw.Raw"],
+        parent: AnnData | Raw,
         axis: int,
-        vals: Union[Mapping, AxisArraysBase, None] = None,
+        vals: Mapping | AxisArraysBase | None = None,
     ):
         self._parent = parent
         if axis not in (0, 1):
@@ -282,7 +292,7 @@ class AxisArraysView(AlignedViewMixin, AxisArraysBase):
     def __init__(
         self,
         parent_mapping: AxisArraysBase,
-        parent_view: "anndata.AnnData",
+        parent_view: AnnData,
         subset_idx: OneDIdx,
     ):
         self.parent_mapping = parent_mapping
@@ -306,7 +316,7 @@ class LayersBase(AlignedMapping):
     axes = (0, 1)
 
     # TODO: I thought I had a more elegant solution to overriding this...
-    def copy(self) -> "Layers":
+    def copy(self) -> Layers:
         d = self._actual_class(self.parent)
         for k, v in self.items():
             d[k] = v.copy()
@@ -314,7 +324,7 @@ def copy(self) -> "Layers":
 
 
 class Layers(AlignedActualMixin, LayersBase):
-    def __init__(self, parent: "anndata.AnnData", vals: Optional[Mapping] = None):
+    def __init__(self, parent: AnnData, vals: Mapping | None = None):
         self._parent = parent
         self._data = dict()
         if vals is not None:
@@ -325,7 +335,7 @@ class LayersView(AlignedViewMixin, LayersBase):
     def __init__(
         self,
         parent_mapping: LayersBase,
-        parent_view: "anndata.AnnData",
+        parent_view: AnnData,
         subset_idx: TwoDIdx,
     ):
         self.parent_mapping = parent_mapping
@@ -351,7 +361,7 @@ def attrname(self) -> str:
         return f"{self.dim}p"
 
     @property
-    def axes(self) -> Tuple[int, int]:
+    def axes(self) -> tuple[int, int]:
         """Axes of the parent this is aligned to"""
         return self._axis, self._axis
 
@@ -364,9 +374,9 @@ def dim(self) -> str:
 class PairwiseArrays(AlignedActualMixin, PairwiseArraysBase):
     def __init__(
         self,
-        parent: "anndata.AnnData",
+        parent: AnnData,
         axis: int,
-        vals: Optional[Mapping] = None,
+        vals: Mapping | None = None,
     ):
         self._parent = parent
         if axis not in (0, 1):
@@ -381,7 +391,7 @@ class PairwiseArraysView(AlignedViewMixin, PairwiseArraysBase):
     def __init__(
         self,
         parent_mapping: PairwiseArraysBase,
-        parent_view: "anndata.AnnData",
+        parent_view: AnnData,
         subset_idx: OneDIdx,
     ):
         self.parent_mapping = parent_mapping
diff --git a/anndata/_core/anndata.py b/anndata/_core/anndata.py
index a4fb2a6e3..b505c8d8e 100644
--- a/anndata/_core/anndata.py
+++ b/anndata/_core/anndata.py
@@ -3,60 +3,66 @@
 """
 from __future__ import annotations
 
-import warnings
 import collections.abc as cabc
+import warnings
 from collections import OrderedDict
+from collections.abc import Iterable, Mapping, MutableMapping, Sequence
 from copy import copy, deepcopy
 from enum import Enum
 from functools import partial, singledispatch
 from pathlib import Path
-from os import PathLike
 from textwrap import dedent
-from typing import Any, Union, Optional, Literal  # Meta
-from typing import Iterable, Sequence, Mapping, MutableMapping  # Generic ABCs
-from typing import Tuple, List  # Generic
+from typing import (  # Meta  # Generic ABCs  # Generic
+    TYPE_CHECKING,
+    Any,
+    Literal,
+)
 
 import h5py
-from natsort import natsorted
 import numpy as np
-from numpy import ma
 import pandas as pd
+from natsort import natsorted
+from numpy import ma
 from pandas.api.types import infer_dtype, is_string_dtype
 from scipy import sparse
-from scipy.sparse import issparse, csr_matrix
+from scipy.sparse import csr_matrix, issparse
 
 from anndata._warnings import ImplicitModificationWarning
-from .raw import Raw
-from .index import _normalize_indices, _subset, Index, Index1D, get_vector
-from .file_backing import AnnDataFileManager, to_memory
+
+from .. import utils
+from ..compat import (
+    CupyArray,
+    CupySparseMatrix,
+    DaskArray,
+    ZappyArray,
+    ZarrArray,
+    _move_adj_mtx,
+)
+from ..logging import anndata_logger as logger
+from ..utils import convert_to_dict, dim_len, ensure_df_homogeneous
 from .access import ElementRef
 from .aligned_mapping import (
     AxisArrays,
     AxisArraysView,
-    PairwiseArrays,
-    PairwiseArraysView,
     Layers,
     LayersView,
+    PairwiseArrays,
+    PairwiseArraysView,
 )
+from .file_backing import AnnDataFileManager, to_memory
+from .index import Index, Index1D, _normalize_indices, _subset, get_vector
+from .raw import Raw
+from .sparse_dataset import sparse_dataset
 from .views import (
     ArrayView,
-    DictView,
     DataFrameView,
-    as_view,
+    DictView,
     _resolve_idxs,
+    as_view,
 )
-from .sparse_dataset import sparse_dataset
-from .. import utils
-from ..utils import convert_to_dict, ensure_df_homogeneous, dim_len
-from ..logging import anndata_logger as logger
-from ..compat import (
-    ZarrArray,
-    ZappyArray,
-    DaskArray,
-    CupyArray,
-    CupySparseMatrix,
-    _move_adj_mtx,
-)
+
+if TYPE_CHECKING:
+    from os import PathLike
 
 
 class StorageType(Enum):
@@ -328,22 +334,22 @@ class AnnData(metaclass=utils.DeprecationMixinMeta):
 
     def __init__(
         self,
-        X: Optional[Union[np.ndarray, sparse.spmatrix, pd.DataFrame]] = None,
-        obs: Optional[Union[pd.DataFrame, Mapping[str, Iterable[Any]]]] = None,
-        var: Optional[Union[pd.DataFrame, Mapping[str, Iterable[Any]]]] = None,
-        uns: Optional[Mapping[str, Any]] = None,
-        obsm: Optional[Union[np.ndarray, Mapping[str, Sequence[Any]]]] = None,
-        varm: Optional[Union[np.ndarray, Mapping[str, Sequence[Any]]]] = None,
-        layers: Optional[Mapping[str, Union[np.ndarray, sparse.spmatrix]]] = None,
-        raw: Optional[Mapping[str, Any]] = None,
-        dtype: Optional[Union[np.dtype, type, str]] = None,
-        shape: Optional[Tuple[int, int]] = None,
-        filename: Optional[PathLike] = None,
-        filemode: Optional[Literal["r", "r+"]] = None,
+        X: np.ndarray | sparse.spmatrix | pd.DataFrame | None = None,
+        obs: pd.DataFrame | Mapping[str, Iterable[Any]] | None = None,
+        var: pd.DataFrame | Mapping[str, Iterable[Any]] | None = None,
+        uns: Mapping[str, Any] | None = None,
+        obsm: np.ndarray | Mapping[str, Sequence[Any]] | None = None,
+        varm: np.ndarray | Mapping[str, Sequence[Any]] | None = None,
+        layers: Mapping[str, np.ndarray | sparse.spmatrix] | None = None,
+        raw: Mapping[str, Any] | None = None,
+        dtype: np.dtype | type | str | None = None,
+        shape: tuple[int, int] | None = None,
+        filename: PathLike | None = None,
+        filemode: Literal["r", "r+"] | None = None,
         asview: bool = False,
         *,
-        obsp: Optional[Union[np.ndarray, Mapping[str, Sequence[Any]]]] = None,
-        varp: Optional[Union[np.ndarray, Mapping[str, Sequence[Any]]]] = None,
+        obsp: np.ndarray | Mapping[str, Sequence[Any]] | None = None,
+        varp: np.ndarray | Mapping[str, Sequence[Any]] | None = None,
         oidx: Index1D = None,
         vidx: Index1D = None,
     ):
@@ -369,7 +375,7 @@ def __init__(
                 filemode=filemode,
             )
 
-    def _init_as_view(self, adata_ref: "AnnData", oidx: Index, vidx: Index):
+    def _init_as_view(self, adata_ref: AnnData, oidx: Index, vidx: Index):
         if adata_ref.isbacked and adata_ref.is_view:
             raise ValueError(
                 "Currently, you cannot index repeatedly into a backed AnnData, "
@@ -643,12 +649,12 @@ def __eq__(self, other):
         )
 
     @property
-    def shape(self) -> Tuple[int, int]:
+    def shape(self) -> tuple[int, int]:
         """Shape of data matrix (:attr:`n_obs`, :attr:`n_vars`)."""
         return self.n_obs, self.n_vars
 
     @property
-    def X(self) -> Optional[Union[np.ndarray, sparse.spmatrix, ArrayView]]:
+    def X(self) -> np.ndarray | sparse.spmatrix | ArrayView | None:
         """Data matrix of shape :attr:`n_obs` × :attr:`n_vars`."""
         if self.isbacked:
             if not self.file.is_open:
@@ -679,7 +685,7 @@ def X(self) -> Optional[Union[np.ndarray, sparse.spmatrix, ArrayView]]:
         #     return X
 
     @X.setter
-    def X(self, value: Optional[Union[np.ndarray, sparse.spmatrix]]):
+    def X(self, value: np.ndarray | sparse.spmatrix | None):
         if value is None:
             if self.isbacked:
                 raise NotImplementedError(
@@ -744,7 +750,7 @@ def X(self):
         self.X = None
 
     @property
-    def layers(self) -> Union[Layers, LayersView]:
+    def layers(self) -> Layers | LayersView:
         """\
         Dictionary-like object with values of the same dimensions as :attr:`X`.
 
@@ -811,7 +817,7 @@ def raw(self) -> Raw:
         return self._raw
 
     @raw.setter
-    def raw(self, value: "AnnData"):
+    def raw(self, value: AnnData):
         if value is None:
             del self.raw
         elif not isinstance(value, AnnData):
@@ -967,7 +973,7 @@ def uns(self):
         self.uns = OrderedDict()
 
     @property
-    def obsm(self) -> Union[AxisArrays, AxisArraysView]:
+    def obsm(self) -> AxisArrays | AxisArraysView:
         """\
         Multi-dimensional annotation of observations
         (mutable structured :class:`~numpy.ndarray`).
@@ -990,7 +996,7 @@ def obsm(self):
         self.obsm = dict()
 
     @property
-    def varm(self) -> Union[AxisArrays, AxisArraysView]:
+    def varm(self) -> AxisArrays | AxisArraysView:
         """\
         Multi-dimensional annotation of variables/features
         (mutable structured :class:`~numpy.ndarray`).
@@ -1013,7 +1019,7 @@ def varm(self):
         self.varm = dict()
 
     @property
-    def obsp(self) -> Union[PairwiseArrays, PairwiseArraysView]:
+    def obsp(self) -> PairwiseArrays | PairwiseArraysView:
         """\
         Pairwise annotation of observations,
         a mutable mapping with array-like values.
@@ -1036,7 +1042,7 @@ def obsp(self):
         self.obsp = dict()
 
     @property
-    def varp(self) -> Union[PairwiseArrays, PairwiseArraysView]:
+    def varp(self) -> PairwiseArrays | PairwiseArraysView:
         """\
         Pairwise annotation of variables/features,
         a mutable mapping with array-like values.
@@ -1058,23 +1064,23 @@ def varp(self, value):
     def varp(self):
         self.varp = dict()
 
-    def obs_keys(self) -> List[str]:
+    def obs_keys(self) -> list[str]:
         """List keys of observation annotation :attr:`obs`."""
         return self._obs.keys().tolist()
 
-    def var_keys(self) -> List[str]:
+    def var_keys(self) -> list[str]:
         """List keys of variable annotation :attr:`var`."""
         return self._var.keys().tolist()
 
-    def obsm_keys(self) -> List[str]:
+    def obsm_keys(self) -> list[str]:
         """List keys of observation annotation :attr:`obsm`."""
         return list(self._obsm.keys())
 
-    def varm_keys(self) -> List[str]:
+    def varm_keys(self) -> list[str]:
         """List keys of variable annotation :attr:`varm`."""
         return list(self._varm.keys())
 
-    def uns_keys(self) -> List[str]:
+    def uns_keys(self) -> list[str]:
         """List keys of unstructured annotation."""
         return sorted(list(self._uns.keys()))
 
@@ -1089,7 +1095,7 @@ def is_view(self) -> bool:
         return self._is_view
 
     @property
-    def filename(self) -> Optional[Path]:
+    def filename(self) -> Path | None:
         """\
         Change to backing mode by setting the filename of a `.h5ad` file.
 
@@ -1101,7 +1107,7 @@ def filename(self) -> Optional[Path]:
         return self.file.filename
 
     @filename.setter
-    def filename(self, filename: Optional[PathLike]):
+    def filename(self, filename: PathLike | None):
         # convert early for later comparison
         filename = None if filename is None else Path(filename)
         # change from backing-mode back to full loading into memory
@@ -1140,7 +1146,7 @@ def _set_backed(self, attr, value):
 
         write_attribute(self.file._file, attr, value)
 
-    def _normalize_indices(self, index: Optional[Index]) -> Tuple[slice, slice]:
+    def _normalize_indices(self, index: Index | None) -> tuple[slice, slice]:
         return _normalize_indices(index, self.obs_names, self.var_names)
 
     # TODO: this is not quite complete...
@@ -1158,7 +1164,7 @@ def __delitem__(self, index: Index):
         if obs == slice(None):
             del self._var.iloc[var, :]
 
-    def __getitem__(self, index: Index) -> "AnnData":
+    def __getitem__(self, index: Index) -> AnnData:
         """Returns a sliced view of the object."""
         oidx, vidx = self._normalize_indices(index)
         return AnnData(self, oidx=oidx, vidx=vidx, asview=True)
@@ -1237,7 +1243,7 @@ def rename_categories(self, key: str, categories: Sequence[Any]):
                             f"Omitting {k1}/{k2} as old categories do not match."
                         )
 
-    def strings_to_categoricals(self, df: Optional[pd.DataFrame] = None):
+    def strings_to_categoricals(self, df: pd.DataFrame | None = None):
         """\
         Transform string annotations to categoricals.
 
@@ -1309,7 +1315,7 @@ def _inplace_subset_obs(self, index: Index1D):
 
     # TODO: Update, possibly remove
     def __setitem__(
-        self, index: Index, val: Union[int, float, np.ndarray, sparse.spmatrix]
+        self, index: Index, val: int | float | np.ndarray | sparse.spmatrix
     ):
         if self.is_view:
             raise ValueError("Object is view and cannot be accessed with `[]`.")
@@ -1324,7 +1330,7 @@ def __setitem__(
     def __len__(self) -> int:
         return self.shape[0]
 
-    def transpose(self) -> "AnnData":
+    def transpose(self) -> AnnData:
         """\
         Transpose whole object.
 
@@ -1404,7 +1410,7 @@ def _get_X(self, use_raw=False, layer=None):
         else:
             return self.X
 
-    def obs_vector(self, k: str, *, layer: Optional[str] = None) -> np.ndarray:
+    def obs_vector(self, k: str, *, layer: str | None = None) -> np.ndarray:
         """\
         Convenience function for returning a 1 dimensional ndarray of values
         from :attr:`X`, :attr:`layers`\\ `[k]`, or :attr:`obs`.
@@ -1436,7 +1442,7 @@ def obs_vector(self, k: str, *, layer: Optional[str] = None) -> np.ndarray:
                 layer = None
         return get_vector(self, k, "obs", "var", layer=layer)
 
-    def var_vector(self, k, *, layer: Optional[str] = None) -> np.ndarray:
+    def var_vector(self, k, *, layer: str | None = None) -> np.ndarray:
         """\
         Convenience function for returning a 1 dimensional ndarray of values
         from :attr:`X`, :attr:`layers`\\ `[k]`, or :attr:`obs`.
@@ -1519,7 +1525,7 @@ def _mutated_copy(self, **kwargs):
             new["raw"] = self.raw.copy()
         return AnnData(**new)
 
-    def to_memory(self, copy=False) -> "AnnData":
+    def to_memory(self, copy=False) -> AnnData:
         """Return a new AnnData object with all backed arrays loaded into memory.
 
         Params
@@ -1564,7 +1570,7 @@ def to_memory(self, copy=False) -> "AnnData":
 
         return AnnData(**new)
 
-    def copy(self, filename: Optional[PathLike] = None) -> "AnnData":
+    def copy(self, filename: PathLike | None = None) -> AnnData:
         """Full copy, optionally on disk."""
         if not self.isbacked:
             if self.is_view and self._has_X():
@@ -1592,14 +1598,14 @@ def copy(self, filename: Optional[PathLike] = None) -> "AnnData":
 
     def concatenate(
         self,
-        *adatas: "AnnData",
+        *adatas: AnnData,
         join: str = "inner",
         batch_key: str = "batch",
         batch_categories: Sequence[Any] = None,
-        uns_merge: Optional[str] = None,
-        index_unique: Optional[str] = "-",
+        uns_merge: str | None = None,
+        index_unique: str | None = "-",
         fill_value=None,
-    ) -> "AnnData":
+    ) -> AnnData:
         """\
         Concatenate along the observations axis.
 
@@ -1811,7 +1817,7 @@ def concatenate(
                [0., 0., 2., 1.],
                [0., 6., 5., 0.]], dtype=float32)
         """
-        from .merge import concat, merge_outer, merge_dataframes, merge_same
+        from .merge import concat, merge_dataframes, merge_outer, merge_same
 
         warnings.warn(
             "The AnnData.concatenate method is deprecated in favour of the "
@@ -1925,9 +1931,9 @@ def _check_dimensions(self, key=None):
 
     def write_h5ad(
         self,
-        filename: Optional[PathLike] = None,
-        compression: Optional[Literal["gzip", "lzf"]] = None,
-        compression_opts: Union[int, Any] = None,
+        filename: PathLike | None = None,
+        compression: Literal["gzip", "lzf"] | None = None,
+        compression_opts: int | Any = None,
         as_dense: Sequence[str] = (),
     ):
         """\
@@ -2047,8 +2053,8 @@ def write_loom(self, filename: PathLike, write_obsm_varm: bool = False):
 
     def write_zarr(
         self,
-        store: Union[MutableMapping, PathLike],
-        chunks: Union[bool, int, Tuple[int, ...], None] = None,
+        store: MutableMapping | PathLike,
+        chunks: bool | int | tuple[int, ...] | None = None,
     ):
         """\
         Write a hierarchical Zarr array store.
@@ -2064,7 +2070,7 @@ def write_zarr(
 
         write_zarr(store, self, chunks=chunks)
 
-    def chunked_X(self, chunk_size: Optional[int] = None):
+    def chunked_X(self, chunk_size: int | None = None):
         """\
         Return an iterator over the rows of the data matrix :attr:`X`.
 
@@ -2087,7 +2093,7 @@ def chunked_X(self, chunk_size: Optional[int] = None):
 
     def chunk_X(
         self,
-        select: Union[int, Sequence[int], np.ndarray] = 1000,
+        select: int | Sequence[int] | np.ndarray = 1000,
         replace: bool = True,
     ):
         """\
diff --git a/anndata/_core/file_backing.py b/anndata/_core/file_backing.py
index eca759dd5..c50a2ea8d 100644
--- a/anndata/_core/file_backing.py
+++ b/anndata/_core/file_backing.py
@@ -1,14 +1,19 @@
+from __future__ import annotations
+
+from collections.abc import Iterator, Mapping
 from functools import singledispatch
-from os import PathLike
 from pathlib import Path
-from typing import Optional, Union, Iterator, Literal
-from collections.abc import Mapping
+from typing import TYPE_CHECKING, Literal
 
 import h5py
 
-from . import anndata
+from ..compat import AwkArray, DaskArray, ZarrArray, ZarrGroup
 from .sparse_dataset import BaseCompressedSparseDataset
-from ..compat import ZarrArray, ZarrGroup, DaskArray, AwkArray
+
+if TYPE_CHECKING:
+    from os import PathLike
+
+    from . import anndata
 
 
 class AnnDataFileManager:
@@ -16,9 +21,9 @@ class AnnDataFileManager:
 
     def __init__(
         self,
-        adata: "anndata.AnnData",
-        filename: Optional[PathLike] = None,
-        filemode: Optional[Literal["r", "r+"]] = None,
+        adata: anndata.AnnData,
+        filename: PathLike | None = None,
+        filemode: Literal["r", "r+"] | None = None,
     ):
         self._adata = adata
         self.filename = filename
@@ -41,13 +46,13 @@ def __iter__(self) -> Iterator[str]:
 
     def __getitem__(
         self, key: str
-    ) -> Union[h5py.Group, h5py.Dataset, BaseCompressedSparseDataset]:
+    ) -> h5py.Group | h5py.Dataset | BaseCompressedSparseDataset:
         return self._file[key]
 
     def __setitem__(
         self,
         key: str,
-        value: Union[h5py.Group, h5py.Dataset, BaseCompressedSparseDataset],
+        value: h5py.Group | h5py.Dataset | BaseCompressedSparseDataset,
     ):
         self._file[key] = value
 
@@ -59,13 +64,13 @@ def filename(self) -> Path:
         return self._filename
 
     @filename.setter
-    def filename(self, filename: Optional[PathLike]):
+    def filename(self, filename: PathLike | None):
         self._filename = None if filename is None else Path(filename)
 
     def open(
         self,
-        filename: Optional[PathLike] = None,
-        filemode: Optional[Literal["r", "r+"]] = None,
+        filename: PathLike | None = None,
+        filemode: Literal["r", "r+"] | None = None,
     ):
         if filename is not None:
             self.filename = filename
diff --git a/anndata/_core/index.py b/anndata/_core/index.py
index 0a14f1841..b98efc8be 100644
--- a/anndata/_core/index.py
+++ b/anndata/_core/index.py
@@ -1,18 +1,21 @@
+from __future__ import annotations
+
 import collections.abc as cabc
+from collections.abc import Sequence
 from functools import singledispatch
 from itertools import repeat
-from typing import Union, Sequence, Optional, Tuple
 
 import h5py
 import numpy as np
 import pandas as pd
-from scipy.sparse import spmatrix, issparse, csc_matrix
+from scipy.sparse import csc_matrix, issparse, spmatrix
+
 from ..compat import AwkArray, DaskArray, Index, Index1D
 
 
 def _normalize_indices(
-    index: Optional[Index], names0: pd.Index, names1: pd.Index
-) -> Tuple[slice, slice]:
+    index: Index | None, names0: pd.Index, names1: pd.Index
+) -> tuple[slice, slice]:
     # deal with tuples of length 1
     if isinstance(index, tuple) and len(index) == 1:
         index = index[0]
@@ -35,17 +38,15 @@ def _normalize_indices(
 
 
 def _normalize_index(
-    indexer: Union[
-        slice,
-        np.integer,
-        int,
-        str,
-        Sequence[Union[int, np.integer]],
-        np.ndarray,
-        pd.Index,
-    ],
+    indexer: slice
+    | np.integer
+    | int
+    | str
+    | Sequence[int | np.integer]
+    | np.ndarray
+    | pd.Index,
     index: pd.Index,
-) -> Union[slice, int, np.ndarray]:  # ndarray of int
+) -> slice | int | np.ndarray:  # ndarray of int
     if not isinstance(index, pd.RangeIndex):
         assert (
             index.dtype != float and index.dtype != int
@@ -104,7 +105,7 @@ def name_idx(i):
         raise IndexError(f"Unknown indexer {indexer!r} of type {type(indexer)}")
 
 
-def unpack_index(index: Index) -> Tuple[Index1D, Index1D]:
+def unpack_index(index: Index) -> tuple[Index1D, Index1D]:
     if not isinstance(index, tuple):
         return index, slice(None)
     elif len(index) == 2:
@@ -116,7 +117,7 @@ def unpack_index(index: Index) -> Tuple[Index1D, Index1D]:
 
 
 @singledispatch
-def _subset(a: Union[np.ndarray, pd.DataFrame], subset_idx: Index):
+def _subset(a: np.ndarray | pd.DataFrame, subset_idx: Index):
     # Select as combination of indexes, not coordinates
     # Correcting for indexing behaviour of np.ndarray
     if all(isinstance(x, cabc.Iterable) for x in subset_idx):
diff --git a/anndata/_core/merge.py b/anndata/_core/merge.py
index d80a12e57..0ecc9e913 100644
--- a/anndata/_core/merge.py
+++ b/anndata/_core/merge.py
@@ -3,34 +3,37 @@
 """
 from __future__ import annotations
 
+import typing
 from collections import OrderedDict
 from collections.abc import (
     Callable,
     Collection,
+    Iterable,
     Mapping,
     MutableSet,
-    Iterable,
     Sequence,
 )
 from functools import reduce, singledispatch
 from itertools import repeat
 from operator import and_, or_, sub
-from typing import Any, Optional, TypeVar, Union, Literal
-import typing
-from warnings import warn, filterwarnings
+from typing import Any, Literal, TypeVar
+from warnings import filterwarnings, warn
 
-from natsort import natsorted
 import numpy as np
 import pandas as pd
-from pandas.api.extensions import ExtensionDtype
+from natsort import natsorted
 from scipy import sparse
 from scipy.sparse import spmatrix
 
-from .anndata import AnnData
-from ..compat import AwkArray, DaskArray, CupySparseMatrix, CupyArray, CupyCSRMatrix
+from anndata._warnings import ExperimentalFeatureWarning
+
+from ..compat import AwkArray, CupyArray, CupyCSRMatrix, CupySparseMatrix, DaskArray
 from ..utils import asarray, dim_len
+from .anndata import AnnData
 from .index import _subset, make_slice
-from anndata._warnings import ExperimentalFeatureWarning
+
+if typing.TYPE_CHECKING:
+    from pandas.api.extensions import ExtensionDtype
 
 T = TypeVar("T")
 
@@ -62,14 +65,14 @@ def copy(self):
     def add(self, val):
         self.dict[val] = None
 
-    def union(self, *vals) -> "OrderedSet":
+    def union(self, *vals) -> OrderedSet:
         return reduce(or_, vals, self)
 
     def discard(self, val):
         if val in self:
             del self.dict[val]
 
-    def difference(self, *vals) -> "OrderedSet":
+    def difference(self, *vals) -> OrderedSet:
         return reduce(sub, vals, self)
 
 
@@ -341,6 +344,7 @@ def _cp_block_diag(mats, format=None, dtype=None):
 
 def _dask_block_diag(mats):
     from itertools import permutations
+
     import dask.array as da
 
     blocks = np.zeros((len(mats), len(mats)), dtype=object)
@@ -361,7 +365,7 @@ def _dask_block_diag(mats):
 ###################
 
 
-def unique_value(vals: Collection[T]) -> Union[T, MissingVal]:
+def unique_value(vals: Collection[T]) -> T | MissingVal:
     """
     Given a collection vals, returns the unique value (if one exists), otherwise
     returns MissingValue.
@@ -373,7 +377,7 @@ def unique_value(vals: Collection[T]) -> Union[T, MissingVal]:
     return unique_val
 
 
-def first(vals: Collection[T]) -> Union[T, MissingVal]:
+def first(vals: Collection[T]) -> T | MissingVal:
     """
     Given a collection of vals, return the first non-missing one.If they're all missing,
     return MissingVal.
@@ -384,7 +388,7 @@ def first(vals: Collection[T]) -> Union[T, MissingVal]:
     return MissingVal
 
 
-def only(vals: Collection[T]) -> Union[T, MissingVal]:
+def only(vals: Collection[T]) -> T | MissingVal:
     """Return the only value in the collection, otherwise MissingVal."""
     if len(vals) == 1:
         return vals[0]
@@ -457,7 +461,7 @@ def merge_only(ds: Collection[Mapping]) -> Mapping:
 
 
 def resolve_merge_strategy(
-    strategy: Union[str, Callable, None]
+    strategy: str | Callable | None,
 ) -> Callable[[Collection[Mapping]], Mapping]:
     if not isinstance(strategy, Callable):
         strategy = MERGE_STRATEGIES[strategy]
@@ -1017,16 +1021,16 @@ def concat_Xs(adatas, reindexers, axis, fill_value):
 
 
 def concat(
-    adatas: Union[Collection[AnnData], "typing.Mapping[str, AnnData]"],
+    adatas: Collection[AnnData] | typing.Mapping[str, AnnData],
     *,
     axis: Literal[0, 1] = 0,
     join: Literal["inner", "outer"] = "inner",
-    merge: Union[StrategiesLiteral, Callable, None] = None,
-    uns_merge: Union[StrategiesLiteral, Callable, None] = None,
-    label: Optional[str] = None,
-    keys: Optional[Collection] = None,
-    index_unique: Optional[str] = None,
-    fill_value: Optional[Any] = None,
+    merge: StrategiesLiteral | Callable | None = None,
+    uns_merge: StrategiesLiteral | Callable | None = None,
+    label: str | None = None,
+    keys: Collection | None = None,
+    index_unique: str | None = None,
+    fill_value: Any | None = None,
     pairwise: bool = False,
 ) -> AnnData:
     """Concatenates AnnData objects along an axis.
diff --git a/anndata/_core/raw.py b/anndata/_core/raw.py
index baa951c56..2b2e27277 100644
--- a/anndata/_core/raw.py
+++ b/anndata/_core/raw.py
@@ -1,27 +1,33 @@
-from typing import Union, Mapping, Sequence, Tuple
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
 
 import h5py
 import numpy as np
 import pandas as pd
-from scipy import sparse
 from scipy.sparse import issparse
 
-from . import anndata
-from .index import _normalize_index, _subset, unpack_index, get_vector
+from ..compat import CupyArray, CupySparseMatrix
 from .aligned_mapping import AxisArrays
+from .index import _normalize_index, _subset, get_vector, unpack_index
 from .sparse_dataset import BaseCompressedSparseDataset, sparse_dataset
 
-from ..compat import CupyArray, CupySparseMatrix
+if TYPE_CHECKING:
+    from collections.abc import Mapping, Sequence
+
+    from scipy import sparse
+
+    from .anndata import AnnData
 
 
 # TODO: Implement views for Raw
 class Raw:
     def __init__(
         self,
-        adata: "anndata.AnnData",
-        X: Union[np.ndarray, sparse.spmatrix, None] = None,
-        var: Union[pd.DataFrame, Mapping[str, Sequence], None] = None,
-        varm: Union[AxisArrays, Mapping[str, np.ndarray], None] = None,
+        adata: AnnData,
+        X: np.ndarray | sparse.spmatrix | None = None,
+        var: pd.DataFrame | Mapping[str, Sequence] | None = None,
+        varm: AxisArrays | Mapping[str, np.ndarray] | None = None,
     ):
         from .anndata import _gen_dataframe
 
@@ -56,7 +62,7 @@ def _get_X(self, layer=None):
         return self.X
 
     @property
-    def X(self) -> Union[BaseCompressedSparseDataset, np.ndarray, sparse.spmatrix]:
+    def X(self) -> BaseCompressedSparseDataset | np.ndarray | sparse.spmatrix:
         # TODO: Handle unsorted array of integer indices for h5py.Datasets
         if not self._adata.isbacked:
             return self._X
@@ -149,7 +155,9 @@ def copy(self):
 
     def to_adata(self):
         """Create full AnnData object."""
-        return anndata.AnnData(
+        from anndata import AnnData
+
+        return AnnData(
             X=self.X.copy(),
             var=self.var.copy(),
             varm=None if self._varm is None else self._varm.copy(),
@@ -191,12 +199,12 @@ def obs_vector(self, k: str) -> np.ndarray:
 # This exists to accommodate AlignedMappings,
 # until we implement a proper RawView or get rid of Raw in favor of modes.
 class _RawViewHack:
-    def __init__(self, raw: Raw, vidx: Union[slice, np.ndarray]):
+    def __init__(self, raw: Raw, vidx: slice | np.ndarray):
         self.parent_raw = raw
         self.vidx = vidx
 
     @property
-    def shape(self) -> Tuple[int, int]:
+    def shape(self) -> tuple[int, int]:
         return self.parent_raw.n_obs, len(self.var_names)
 
     @property
diff --git a/anndata/_core/sparse_dataset.py b/anndata/_core/sparse_dataset.py
index 83eb4befa..453b0a590 100644
--- a/anndata/_core/sparse_dataset.py
+++ b/anndata/_core/sparse_dataset.py
@@ -12,17 +12,18 @@
 # - think about supporting the COO format
 from __future__ import annotations
 
-from abc import ABC
 import collections.abc as cabc
-from itertools import accumulate, chain
-from typing import Literal, Union, NamedTuple, Tuple, Sequence, Iterable, Type
 import warnings
+from abc import ABC
+from itertools import accumulate, chain
+from typing import TYPE_CHECKING, Literal, NamedTuple
 
 import h5py
 import numpy as np
 import scipy.sparse as ss
 from scipy.sparse import _sparsetools
-from anndata.compat import ZarrGroup, H5Group
+
+from anndata.compat import H5Group, ZarrGroup
 
 from ..compat import _read_attr
 
@@ -32,13 +33,16 @@
 except ImportError:
     _cs_matrix = ss.spmatrix
 
-from .index import unpack_index, Index, _subset
+from .index import Index, _subset, unpack_index
+
+if TYPE_CHECKING:
+    from collections.abc import Iterable, Sequence
 
 
 class BackedFormat(NamedTuple):
     format: str
-    backed_type: Type["BackedSparseMatrix"]
-    memory_type: Type[ss.spmatrix]
+    backed_type: type[BackedSparseMatrix]
+    memory_type: type[ss.spmatrix]
 
 
 class BackedSparseMatrix(_cs_matrix):
@@ -192,7 +196,7 @@ def slice_as_int(s: slice, l: int) -> int:
 
 def get_compressed_vectors(
     x: BackedSparseMatrix, row_idxs: Iterable[int]
-) -> Tuple[Sequence, Sequence, Sequence]:
+) -> tuple[Sequence, Sequence, Sequence]:
     slices = [slice(*(x.indptr[i : i + 2])) for i in row_idxs]
     data = np.concatenate([x.data[s] for s in slices])
     indices = np.concatenate([x.indices[s] for s in slices])
@@ -202,7 +206,7 @@ def get_compressed_vectors(
 
 def get_compressed_vector(
     x: BackedSparseMatrix, idx: int
-) -> Tuple[Sequence, Sequence, Sequence]:
+) -> tuple[Sequence, Sequence, Sequence]:
     s = slice(*(x.indptr[idx : idx + 2]))
     data = x.data[s]
     indices = x.indices[s]
@@ -217,14 +221,14 @@ def get_format(data: ss.spmatrix) -> str:
     raise ValueError(f"Data type {type(data)} is not supported.")
 
 
-def get_memory_class(format: str) -> Type[ss.spmatrix]:
+def get_memory_class(format: str) -> type[ss.spmatrix]:
     for fmt, _, memory_class in FORMATS:
         if format == fmt:
             return memory_class
     raise ValueError(f"Format string {format} is not supported.")
 
 
-def get_backed_class(format: str) -> Type[BackedSparseMatrix]:
+def get_backed_class(format: str) -> type[BackedSparseMatrix]:
     for fmt, backed_class, _ in FORMATS:
         if format == fmt:
             return backed_class
@@ -284,7 +288,7 @@ def name(self) -> str:
         return self.group.name
 
     @property
-    def shape(self) -> Tuple[int, int]:
+    def shape(self) -> tuple[int, int]:
         shape = _read_attr(self.group.attrs, "shape", None)
         if shape is None:
             # TODO warn
@@ -304,7 +308,7 @@ def value(self) -> ss.spmatrix:
     def __repr__(self) -> str:
         return f"{type(self).__name__}: backend {self.backend}, shape {self.shape}, data_dtype {self.dtype}"
 
-    def __getitem__(self, index: Union[Index, Tuple[()]]) -> Union[float, ss.spmatrix]:
+    def __getitem__(self, index: Index | tuple[()]) -> float | ss.spmatrix:
         row, col = self._normalize_index(index)
         mtx = self._to_backed()
         sub = mtx[row, col]
@@ -316,8 +320,8 @@ def __getitem__(self, index: Union[Index, Tuple[()]]) -> Union[float, ss.spmatri
             return sub
 
     def _normalize_index(
-        self, index: Union[Index, Tuple[()]]
-    ) -> Tuple[np.ndarray, np.ndarray]:
+        self, index: Index | tuple[()]
+    ) -> tuple[np.ndarray, np.ndarray]:
         if index == ():
             index = slice(None)
         row, col = unpack_index(index)
@@ -325,7 +329,7 @@ def _normalize_index(
             row, col = np.ix_(row, col)
         return row, col
 
-    def __setitem__(self, index: Union[Index, Tuple[()]], value):
+    def __setitem__(self, index: Index | tuple[()], value):
         warnings.warn(
             "__setitem__ will likely be removed in the near future. We do not recommend relying on its stability.",
             PendingDeprecationWarning,
diff --git a/anndata/_core/views.py b/anndata/_core/views.py
index aa8dbb625..36faf5fbe 100644
--- a/anndata/_core/views.py
+++ b/anndata/_core/views.py
@@ -1,32 +1,36 @@
 from __future__ import annotations
 
+import warnings
 from contextlib import contextmanager
 from copy import deepcopy
-from collections.abc import Sequence, KeysView, Callable, Iterable
 from functools import reduce, singledispatch, wraps
-from typing import Any, Literal
-import warnings
+from typing import TYPE_CHECKING, Any, Literal
 
 import numpy as np
 import pandas as pd
 from pandas.api.types import is_bool_dtype
 from scipy import sparse
 
-import anndata
 from anndata._warnings import ImplicitModificationWarning
-from .access import ElementRef
+
 from ..compat import (
-    ZappyArray,
     AwkArray,
-    DaskArray,
     CupyArray,
     CupyCSCMatrix,
     CupyCSRMatrix,
+    DaskArray,
+    ZappyArray,
 )
+from .access import ElementRef
+
+if TYPE_CHECKING:
+    from collections.abc import Callable, Iterable, KeysView, Sequence
+
+    from anndata import AnnData
 
 
 @contextmanager
-def view_update(adata_view: anndata.AnnData, attr_name: str, keys: tuple[str, ...]):
+def view_update(adata_view: AnnData, attr_name: str, keys: tuple[str, ...]):
     """Context manager for updating a view of an AnnData object.
 
     Contains logic for "actualizing" a view. Yields the object to be modified in-place.
@@ -79,7 +83,7 @@ class _ViewMixin(_SetItemMixin):
     def __init__(
         self,
         *args,
-        view_args: tuple["anndata.AnnData", str, tuple[str, ...]] = None,
+        view_args: tuple[AnnData, str, tuple[str, ...]] = None,
         **kwargs,
     ):
         if view_args is not None:
@@ -100,7 +104,7 @@ class ArrayView(_SetItemMixin, np.ndarray):
     def __new__(
         cls,
         input_array: Sequence[Any],
-        view_args: tuple["anndata.AnnData", str, tuple[str, ...]] = None,
+        view_args: tuple[AnnData, str, tuple[str, ...]] = None,
     ):
         arr = np.asanyarray(input_array).view(cls)
 
@@ -172,7 +176,7 @@ class DaskArrayView(_SetItemMixin, DaskArray):
     def __new__(
         cls,
         input_array: DaskArray,
-        view_args: tuple["anndata.AnnData", str, tuple[str, ...]] = None,
+        view_args: tuple[AnnData, str, tuple[str, ...]] = None,
     ):
         arr = super().__new__(
             cls,
@@ -226,7 +230,7 @@ class CupyArrayView(_ViewMixin, CupyArray):
     def __new__(
         cls,
         input_array: Sequence[Any],
-        view_args: tuple["anndata.AnnData", str, tuple[str, ...]] = None,
+        view_args: tuple[AnnData, str, tuple[str, ...]] = None,
     ):
         import cupy as cp
 
@@ -316,9 +320,10 @@ def as_view_cupy_csc(mtx, view_args):
 
 
 try:
-    from ..compat import awkward as ak
     import weakref
 
+    from ..compat import awkward as ak
+
     # Registry to store weak references from AwkwardArrayViews to their parent AnnData container
     _registry = weakref.WeakValueDictionary()
     _PARAM_NAME = "_view_args"
diff --git a/anndata/_io/__init__.py b/anndata/_io/__init__.py
index f305d42ab..7bb6ba506 100644
--- a/anndata/_io/__init__.py
+++ b/anndata/_io/__init__.py
@@ -1,3 +1,6 @@
+from __future__ import annotations
+
+from .h5ad import read_h5ad, write_h5ad
 from .read import (
     read_csv,
     read_excel,
@@ -8,7 +11,6 @@
     read_umi_tools,
     read_zarr,
 )
-from .h5ad import read_h5ad, write_h5ad
 from .write import write_csvs, write_loom
 
 
diff --git a/anndata/_io/h5ad.py b/anndata/_io/h5ad.py
index 5ba94e8bd..bfddc6504 100644
--- a/anndata/_io/h5ad.py
+++ b/anndata/_io/h5ad.py
@@ -1,41 +1,50 @@
+from __future__ import annotations
+
 import re
 from functools import partial
-from warnings import warn
 from pathlib import Path
 from types import MappingProxyType
-from typing import Callable, Type, TypeVar, Union, Literal
-from typing import Collection, Sequence, Mapping
+from typing import (
+    TYPE_CHECKING,
+    Callable,
+    Literal,
+    TypeVar,
+)
+from warnings import warn
 
 import h5py
 import numpy as np
 import pandas as pd
 from scipy import sparse
 
-from .._core.sparse_dataset import BaseCompressedSparseDataset
-from .._core.file_backing import AnnDataFileManager, filename
+from anndata._warnings import OldFormatWarning
+
 from .._core.anndata import AnnData
+from .._core.file_backing import AnnDataFileManager, filename
+from .._core.sparse_dataset import BaseCompressedSparseDataset
 from ..compat import (
-    _from_fixed_length_strings,
-    _decode_structured_array,
     _clean_uns,
+    _decode_structured_array,
+    _from_fixed_length_strings,
 )
 from ..experimental import read_dispatched
+from .specs import read_elem, write_elem
 from .utils import (
     H5PY_V3,
+    _read_legacy_raw,
+    idx_chunks_along_axis,
     report_read_key_on_error,
     report_write_key_on_error,
-    idx_chunks_along_axis,
-    _read_legacy_raw,
 )
-from .specs import read_elem, write_elem
-from anndata._warnings import OldFormatWarning
 
+if TYPE_CHECKING:
+    from collections.abc import Collection, Mapping, Sequence
 
 T = TypeVar("T")
 
 
 def write_h5ad(
-    filepath: Union[Path, str],
+    filepath: Path | str,
     adata: AnnData,
     *,
     as_dense: Sequence[str] = (),
@@ -122,7 +131,7 @@ def write_sparse_as_dense(f, key, value, dataset_kwargs=MappingProxyType({})):
         del f[key]
 
 
-def read_h5ad_backed(filename: Union[str, Path], mode: Literal["r", "r+"]) -> AnnData:
+def read_h5ad_backed(filename: str | Path, mode: Literal["r", "r+"]) -> AnnData:
     d = dict(filename=filename, filemode=mode)
 
     f = h5py.File(filename, mode)
@@ -151,11 +160,11 @@ def read_h5ad_backed(filename: Union[str, Path], mode: Literal["r", "r+"]) -> An
 
 
 def read_h5ad(
-    filename: Union[str, Path],
-    backed: Union[Literal["r", "r+"], bool, None] = None,
+    filename: str | Path,
+    backed: Literal["r", "r+"] | bool | None = None,
     *,
     as_sparse: Sequence[str] = (),
-    as_sparse_fmt: Type[sparse.spmatrix] = sparse.csr_matrix,
+    as_sparse_fmt: type[sparse.spmatrix] = sparse.csr_matrix,
     chunk_size: int = 6000,  # TODO, probably make this 2d chunks
 ) -> AnnData:
     """\
@@ -256,7 +265,7 @@ def callback(func, elem_name: str, elem, iospec):
 
 
 def _read_raw(
-    f: Union[h5py.File, AnnDataFileManager],
+    f: h5py.File | AnnDataFileManager,
     as_sparse: Collection[str] = (),
     rdasp: Callable[[h5py.Dataset], sparse.spmatrix] = None,
     *,
diff --git a/anndata/_io/read.py b/anndata/_io/read.py
index 91115a81b..68f7fbd27 100644
--- a/anndata/_io/read.py
+++ b/anndata/_io/read.py
@@ -1,11 +1,12 @@
-from pathlib import Path
+from __future__ import annotations
+
+import bz2
+import gzip
+from collections import OrderedDict
 from os import PathLike, fspath
+from pathlib import Path
 from types import MappingProxyType
-from typing import Union, Optional, Mapping, Tuple
-from typing import Iterable, Iterator, Generator
-from collections import OrderedDict
-import gzip
-import bz2
+from typing import TYPE_CHECKING
 from warnings import warn
 
 import h5py
@@ -17,6 +18,9 @@
 from ..compat import _deprecate_positional_args
 from .utils import is_float
 
+if TYPE_CHECKING:
+    from collections.abc import Generator, Iterable, Iterator, Mapping
+
 try:
     from .zarr import read_zarr
 except ImportError as _e:
@@ -27,9 +31,9 @@ def read_zarr(*_, **__):
 
 
 def read_csv(
-    filename: Union[PathLike, Iterator[str]],
-    delimiter: Optional[str] = ",",
-    first_column_names: Optional[bool] = None,
+    filename: PathLike | Iterator[str],
+    delimiter: str | None = ",",
+    first_column_names: bool | None = None,
     dtype: str = "float32",
 ) -> AnnData:
     """\
@@ -53,9 +57,7 @@ def read_csv(
     return read_text(filename, delimiter, first_column_names, dtype)
 
 
-def read_excel(
-    filename: PathLike, sheet: Union[str, int], dtype: str = "float32"
-) -> AnnData:
+def read_excel(filename: PathLike, sheet: str | int, dtype: str = "float32") -> AnnData:
     """\
     Read `.xlsx` (Excel) file.
 
@@ -137,7 +139,7 @@ def read_hdf(filename: PathLike, key: str) -> AnnData:
 
 def _fmt_loom_axis_attrs(
     input: Mapping, idx_name: str, dimm_mapping: Mapping[str, Iterable[str]]
-) -> Tuple[pd.DataFrame, Mapping[str, np.ndarray]]:
+) -> tuple[pd.DataFrame, Mapping[str, np.ndarray]]:
     axis_df = pd.DataFrame()
     axis_mapping = {}
     for key, names in dimm_mapping.items():
@@ -163,9 +165,9 @@ def read_loom(
     cleanup: bool = False,
     X_name: str = "spliced",
     obs_names: str = "CellID",
-    obsm_names: Optional[Mapping[str, Iterable[str]]] = None,
+    obsm_names: Mapping[str, Iterable[str]] | None = None,
     var_names: str = "Gene",
-    varm_names: Optional[Mapping[str, Iterable[str]]] = None,
+    varm_names: Mapping[str, Iterable[str]] | None = None,
     dtype: str = "float32",
     obsm_mapping: Mapping[str, Iterable[str]] = MappingProxyType({}),
     varm_mapping: Mapping[str, Iterable[str]] = MappingProxyType({}),
@@ -320,9 +322,9 @@ def read_mtx(filename: PathLike, dtype: str = "float32") -> AnnData:
 
 
 def read_text(
-    filename: Union[PathLike, Iterator[str]],
-    delimiter: Optional[str] = None,
-    first_column_names: Optional[bool] = None,
+    filename: PathLike | Iterator[str],
+    delimiter: str | None = None,
+    first_column_names: bool | None = None,
     dtype: str = "float32",
 ) -> AnnData:
     """\
@@ -368,8 +370,8 @@ def _iter_lines(file_like: Iterable[str]) -> Generator[str, None, None]:
 
 def _read_text(
     f: Iterator[str],
-    delimiter: Optional[str],
-    first_column_names: Optional[bool],
+    delimiter: str | None,
+    first_column_names: bool | None,
     dtype: str,
 ) -> AnnData:
     comments = []
diff --git a/anndata/_io/specs/__init__.py b/anndata/_io/specs/__init__.py
index 28281a1e0..ceff8b3d6 100644
--- a/anndata/_io/specs/__init__.py
+++ b/anndata/_io/specs/__init__.py
@@ -1,6 +1,15 @@
+from __future__ import annotations
+
 from . import methods
-from .registry import write_elem, get_spec, read_elem, Reader, Writer, IOSpec
-from .registry import _REGISTRY  # noqa: F401
+from .registry import (
+    _REGISTRY,  # noqa: F401
+    IOSpec,
+    Reader,
+    Writer,
+    get_spec,
+    read_elem,
+    write_elem,
+)
 
 __all__ = [
     "methods",
diff --git a/anndata/_io/specs/methods.py b/anndata/_io/specs/methods.py
index d608c5806..00cd66ea7 100644
--- a/anndata/_io/specs/methods.py
+++ b/anndata/_io/specs/methods.py
@@ -1,11 +1,10 @@
 from __future__ import annotations
 
-from os import PathLike
 from collections.abc import Mapping
-from itertools import product
 from functools import partial
-from typing import Union, Literal
+from itertools import product
 from types import MappingProxyType
+from typing import TYPE_CHECKING, Literal
 from warnings import warn
 
 import h5py
@@ -15,24 +14,30 @@
 
 import anndata as ad
 from anndata import AnnData, Raw
+from anndata._core import views
 from anndata._core.index import _normalize_indices
 from anndata._core.merge import intersect_keys
 from anndata._core.sparse_dataset import CSCDataset, CSRDataset, sparse_dataset
-from anndata._core import views
+from anndata._io.utils import H5PY_V3, check_key
+from anndata._warnings import OldFormatWarning
 from anndata.compat import (
+    AwkArray,
+    CupyArray,
+    CupyCSCMatrix,
+    CupyCSRMatrix,
+    DaskArray,
     ZarrArray,
     ZarrGroup,
-    DaskArray,
-    _read_attr,
-    _from_fixed_length_strings,
     _decode_structured_array,
+    _from_fixed_length_strings,
+    _read_attr,
 )
-from anndata._io.utils import check_key, H5PY_V3
-from anndata._warnings import OldFormatWarning
-from anndata.compat import AwkArray, CupyArray, CupyCSRMatrix, CupyCSCMatrix
 
 from .registry import _REGISTRY, IOSpec, read_elem, read_elem_partial
 
+if TYPE_CHECKING:
+    from os import PathLike
+
 H5Array = h5py.Dataset
 H5Group = h5py.Group
 H5File = h5py.File
@@ -736,7 +741,7 @@ def read_dataframe_0_1_0(elem, _reader):
     return df
 
 
-def read_series(dataset: h5py.Dataset) -> Union[np.ndarray, pd.Categorical]:
+def read_series(dataset: h5py.Dataset) -> np.ndarray | pd.Categorical:
     # For reading older dataframes
     if "categories" in dataset.attrs:
         if isinstance(dataset, ZarrArray):
diff --git a/anndata/_io/specs/registry.py b/anndata/_io/specs/registry.py
index 1a20fb320..1f0b137f4 100644
--- a/anndata/_io/specs/registry.py
+++ b/anndata/_io/specs/registry.py
@@ -1,14 +1,16 @@
 from __future__ import annotations
 
-from collections.abc import Mapping, Callable, Iterable
+from collections.abc import Callable, Iterable, Mapping
 from dataclasses import dataclass
 from functools import singledispatch, wraps
 from types import MappingProxyType
-from typing import Any, Union
+from typing import TYPE_CHECKING, Any
 
+from anndata._io.utils import report_read_key_on_error, report_write_key_on_error
 from anndata.compat import _read_attr
-from anndata._types import StorageType, GroupStorageType
-from anndata._io.utils import report_write_key_on_error, report_read_key_on_error
+
+if TYPE_CHECKING:
+    from anndata._types import GroupStorageType, StorageType
 
 # TODO: This probably should be replaced by a hashable Mapping due to conversion b/w "_" and "-"
 # TODO: Should filetype be included in the IOSpec if it changes the encoding? Or does the intent that these things be "the same" overrule that?
@@ -66,7 +68,7 @@ def __init__(self):
         self.write: dict[
             tuple[type, type | tuple[type, str], frozenset[str]], Callable
         ] = {}
-        self.write_specs: dict[Union[type, tuple[type, str]], IOSpec] = {}
+        self.write_specs: dict[type | tuple[type, str], IOSpec] = {}
 
     def register_write(
         self,
@@ -226,9 +228,7 @@ def _iter_patterns(elem):
 
 
 class Reader:
-    def __init__(
-        self, registry: IORegistry, callback: Union[Callable, None] = None
-    ) -> None:
+    def __init__(self, registry: IORegistry, callback: Callable | None = None) -> None:
         self.registry = registry
         self.callback = callback
 
@@ -255,18 +255,16 @@ class Writer:
     def __init__(
         self,
         registry: IORegistry,
-        callback: Union[
-            Callable[
-                [
-                    GroupStorageType,
-                    str,
-                    StorageType,
-                    dict,
-                ],
-                None,
+        callback: Callable[
+            [
+                GroupStorageType,
+                str,
+                StorageType,
+                dict,
             ],
             None,
-        ] = None,
+        ]
+        | None = None,
     ):
         self.registry = registry
         self.callback = callback
@@ -290,6 +288,7 @@ def write_elem(
     ):
         from functools import partial
         from pathlib import PurePosixPath
+
         import h5py
 
         if isinstance(store, h5py.File):
diff --git a/anndata/_io/utils.py b/anndata/_io/utils.py
index 33aca7cde..e6bccde01 100644
--- a/anndata/_io/utils.py
+++ b/anndata/_io/utils.py
@@ -4,12 +4,13 @@
 from typing import Callable, Literal
 from warnings import warn
 
-from packaging import version
 import h5py
+from packaging import version
 
-from .._core.sparse_dataset import BaseCompressedSparseDataset
 from anndata.compat import H5Group, ZarrGroup, add_note
 
+from .._core.sparse_dataset import BaseCompressedSparseDataset
+
 # For allowing h5py v3
 # https://github.com/scverse/anndata/issues/442
 H5PY_V3 = version.parse(h5py.__version__).major >= 3
diff --git a/anndata/_io/write.py b/anndata/_io/write.py
index 28ce012d0..5a4d2ca62 100644
--- a/anndata/_io/write.py
+++ b/anndata/_io/write.py
@@ -1,15 +1,20 @@
+from __future__ import annotations
+
+import math
 import warnings
-from pathlib import Path
 from os import PathLike, fspath
+from pathlib import Path
+from typing import TYPE_CHECKING
 
-import pandas as pd
-import math
 import numpy as np
+import pandas as pd
 from scipy.sparse import issparse
 
-from .. import AnnData
-from ..logging import get_logger
 from .._warnings import WriteWarning
+from ..logging import get_logger
+
+if TYPE_CHECKING:
+    from .. import AnnData
 
 logger = get_logger(__name__)
 
diff --git a/anndata/_io/zarr.py b/anndata/_io/zarr.py
index d85e1fc19..022ee8a1d 100644
--- a/anndata/_io/zarr.py
+++ b/anndata/_io/zarr.py
@@ -1,32 +1,36 @@
-from collections.abc import MutableMapping
+from __future__ import annotations
+
 from pathlib import Path
-from typing import TypeVar, Union
+from typing import TYPE_CHECKING, TypeVar
 from warnings import warn
 
 import numpy as np
-from scipy import sparse
 import pandas as pd
 import zarr
+from scipy import sparse
+
+from anndata._warnings import OldFormatWarning
 
 from .._core.anndata import AnnData
 from ..compat import (
-    _from_fixed_length_strings,
     _clean_uns,
+    _from_fixed_length_strings,
 )
 from ..experimental import read_dispatched, write_dispatched
+from .specs import read_elem
 from .utils import (
-    report_read_key_on_error,
     _read_legacy_raw,
+    report_read_key_on_error,
 )
-from .specs import read_elem
-from anndata._warnings import OldFormatWarning
 
+if TYPE_CHECKING:
+    from collections.abc import MutableMapping
 
 T = TypeVar("T")
 
 
 def write_zarr(
-    store: Union[MutableMapping, str, Path],
+    store: MutableMapping | str | Path,
     adata: AnnData,
     chunks=None,
     **ds_kwargs,
@@ -50,7 +54,7 @@ def callback(func, s, k, elem, dataset_kwargs, iospec):
     write_dispatched(f, "/", adata, callback=callback, dataset_kwargs=ds_kwargs)
 
 
-def read_zarr(store: Union[str, Path, MutableMapping, zarr.Group]) -> AnnData:
+def read_zarr(store: str | Path | MutableMapping | zarr.Group) -> AnnData:
     """\
     Read from a hierarchical Zarr array store.
 
diff --git a/anndata/_types.py b/anndata/_types.py
index d5b6b1c5c..7f57e380f 100644
--- a/anndata/_types.py
+++ b/anndata/_types.py
@@ -1,6 +1,8 @@
 """
 Defines some useful types for this library. Should probably be cleaned up before thinking about exporting.
 """
+from __future__ import annotations
+
 from typing import Union
 
 from anndata.compat import H5Array, H5Group, ZarrArray, ZarrGroup
diff --git a/anndata/_warnings.py b/anndata/_warnings.py
index 5bc0c461c..1820a6d96 100644
--- a/anndata/_warnings.py
+++ b/anndata/_warnings.py
@@ -1,3 +1,6 @@
+from __future__ import annotations
+
+
 class WriteWarning(UserWarning):
     pass
 
diff --git a/anndata/compat/__init__.py b/anndata/compat/__init__.py
index 1507f1be4..d6ab5c2f3 100644
--- a/anndata/compat/__init__.py
+++ b/anndata/compat/__init__.py
@@ -1,20 +1,20 @@
 from __future__ import annotations
 
+import os
+from codecs import decode
+from collections.abc import Mapping
 from contextlib import AbstractContextManager
 from dataclasses import dataclass, field
-
 from functools import singledispatch, wraps
-from codecs import decode
-from inspect import signature, Parameter
-import os
+from inspect import Parameter, signature
 from pathlib import Path
-from typing import Any, Tuple, Union, Mapping, Optional
+from typing import Any, Union
 from warnings import warn
 
 import h5py
-from scipy.sparse import spmatrix, issparse
 import numpy as np
 import pandas as pd
+from scipy.sparse import issparse, spmatrix
 
 from .exceptiongroups import add_note  # noqa: F401
 
@@ -24,7 +24,7 @@ class Empty:
 
 
 Index1D = Union[slice, int, str, np.int64, np.ndarray]
-Index = Union[Index1D, Tuple[Index1D, Index1D], spmatrix]
+Index = Union[Index1D, tuple[Index1D, Index1D], spmatrix]
 H5Group = h5py.Group
 H5Array = h5py.Dataset
 
@@ -105,12 +105,16 @@ def __repr__():
 
 
 try:
+    from cupy import ndarray as CupyArray
     from cupyx.scipy.sparse import (
-        spmatrix as CupySparseMatrix,
-        csr_matrix as CupyCSRMatrix,
         csc_matrix as CupyCSCMatrix,
     )
-    from cupy import ndarray as CupyArray
+    from cupyx.scipy.sparse import (
+        csr_matrix as CupyCSRMatrix,
+    )
+    from cupyx.scipy.sparse import (
+        spmatrix as CupySparseMatrix,
+    )
 except ImportError:
 
     class CupySparseMatrix:
@@ -140,7 +144,7 @@ def __repr__():
 
 
 @singledispatch
-def _read_attr(attrs: Mapping, name: str, default: Optional[Any] = Empty):
+def _read_attr(attrs: Mapping, name: str, default: Any | None = Empty):
     if default is Empty:
         return attrs[name]
     else:
@@ -149,7 +153,7 @@ def _read_attr(attrs: Mapping, name: str, default: Optional[Any] = Empty):
 
 @_read_attr.register(h5py.AttributeManager)
 def _read_attr_hdf5(
-    attrs: h5py.AttributeManager, name: str, default: Optional[Any] = Empty
+    attrs: h5py.AttributeManager, name: str, default: Any | None = Empty
 ):
     """
     Read an HDF5 attribute and perform all necessary conversions.
@@ -200,7 +204,7 @@ def _from_fixed_length_strings(value):
 
 
 def _decode_structured_array(
-    arr: np.ndarray, dtype: Optional[np.dtype] = None, copy: bool = False
+    arr: np.ndarray, dtype: np.dtype | None = None, copy: bool = False
 ) -> np.ndarray:
     """
     h5py 3.0 now reads all strings as bytes. There is a helper method which can convert these to strings,
@@ -250,7 +254,7 @@ def _to_fixed_length_strings(value: np.ndarray) -> np.ndarray:
 #############################
 
 
-def _clean_uns(adata: "AnnData"):  # noqa: F821
+def _clean_uns(adata: AnnData):  # noqa: F821
     """
     Compat function for when categorical keys were stored in uns.
     This used to be buggy because when storing categorical columns in obs and var with
@@ -342,7 +346,7 @@ def inner_f(*args, **kwargs):
 
             # extra_args > 0
             args_msg = [
-                "{}={}".format(name, arg)
+                f"{name}={arg}"
                 for name, arg in zip(kwonly_args[:extra_args], args[-extra_args:])
             ]
             args_msg = ", ".join(args_msg)
diff --git a/anndata/compat/exceptiongroups.py b/anndata/compat/exceptiongroups.py
index f64090017..49d6c3a65 100644
--- a/anndata/compat/exceptiongroups.py
+++ b/anndata/compat/exceptiongroups.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import sys
 
 
diff --git a/anndata/core.py b/anndata/core.py
index c4b254c0e..8e6ef0382 100644
--- a/anndata/core.py
+++ b/anndata/core.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from warnings import warn
 
 warn("Please only import from anndata, not anndata.core", DeprecationWarning)
diff --git a/anndata/experimental/__init__.py b/anndata/experimental/__init__.py
index 13667e214..486f14e8d 100644
--- a/anndata/experimental/__init__.py
+++ b/anndata/experimental/__init__.py
@@ -1,12 +1,12 @@
 from __future__ import annotations
 
-from .multi_files import AnnCollection
-from .pytorch import AnnLoader
+from anndata._core.sparse_dataset import CSCDataset, CSRDataset, sparse_dataset
+from anndata._io.specs import IOSpec, read_elem, write_elem
 
-from anndata._io.specs import read_elem, write_elem, IOSpec
-from anndata._core.sparse_dataset import sparse_dataset, CSRDataset, CSCDataset
 from ._dispatch_io import read_dispatched, write_dispatched
 from .merge import concat_on_disk
+from .multi_files import AnnCollection
+from .pytorch import AnnLoader
 
 __all__ = [
     "AnnCollection",
diff --git a/anndata/experimental/_dispatch_io.py b/anndata/experimental/_dispatch_io.py
index 2df14b4f1..4df4d417a 100644
--- a/anndata/experimental/_dispatch_io.py
+++ b/anndata/experimental/_dispatch_io.py
@@ -1,11 +1,11 @@
 from __future__ import annotations
 
 from types import MappingProxyType
-from typing import Callable, Any
+from typing import TYPE_CHECKING, Any, Callable
 
-
-from anndata._io.specs import IOSpec
-from anndata._types import StorageType, GroupStorageType
+if TYPE_CHECKING:
+    from anndata._io.specs import IOSpec
+    from anndata._types import GroupStorageType, StorageType
 
 
 def read_dispatched(
@@ -39,7 +39,7 @@ def read_dispatched(
 
     :doc:`/tutorials/notebooks/{read,write}_dispatched`
     """
-    from anndata._io.specs import Reader, _REGISTRY
+    from anndata._io.specs import _REGISTRY, Reader
 
     reader = Reader(_REGISTRY, callback=callback)
 
@@ -90,7 +90,7 @@ def write_dispatched(
 
     :doc:`/tutorials/notebooks/{read,write}_dispatched`
     """
-    from anndata._io.specs import Writer, _REGISTRY
+    from anndata._io.specs import _REGISTRY, Writer
 
     writer = Writer(_REGISTRY, callback=callback)
 
diff --git a/anndata/experimental/merge.py b/anndata/experimental/merge.py
index 2cc91c5b2..87f986c7c 100644
--- a/anndata/experimental/merge.py
+++ b/anndata/experimental/merge.py
@@ -1,18 +1,14 @@
+from __future__ import annotations
+
 import os
 import shutil
+from collections.abc import Collection, Iterable, Mapping, MutableMapping, Sequence
 from functools import singledispatch
 from pathlib import Path
 from typing import (
     Any,
     Callable,
-    Collection,
-    Iterable,
     Literal,
-    Mapping,
-    Optional,
-    Sequence,
-    Union,
-    MutableMapping,
 )
 
 import numpy as np
@@ -104,12 +100,12 @@ def _gen_slice_to_append(
 
 
 @singledispatch
-def as_group(store, *args, **kwargs) -> Union[ZarrGroup, H5Group]:
+def as_group(store, *args, **kwargs) -> ZarrGroup | H5Group:
     raise NotImplementedError("This is not yet implemented.")
 
 
-@as_group.register
-def _(store: os.PathLike, *args, **kwargs) -> Union[ZarrGroup, H5Group]:
+@as_group.register(os.PathLike)
+def _(store: os.PathLike, *args, **kwargs) -> ZarrGroup | H5Group:
     if store.suffix == ".h5ad":
         import h5py
 
@@ -119,8 +115,8 @@ def _(store: os.PathLike, *args, **kwargs) -> Union[ZarrGroup, H5Group]:
     return zarr.open_group(store, *args, **kwargs)
 
 
-@as_group.register
-def _(store: str, *args, **kwargs) -> Union[ZarrGroup, H5Group]:
+@as_group.register(str)
+def _(store: str, *args, **kwargs) -> ZarrGroup | H5Group:
     return as_group(Path(store), *args, **kwargs)
 
 
@@ -135,7 +131,7 @@ def _(store, *args, **kwargs):
 ###################
 
 
-def read_as_backed(group: Union[ZarrGroup, H5Group]):
+def read_as_backed(group: ZarrGroup | H5Group):
     """
     Read the group until
     BaseCompressedSparseDataset, Array or EAGER_TYPES are encountered.
@@ -156,7 +152,7 @@ def callback(func, elem_name: str, elem, iospec):
     return read_dispatched(group, callback=callback)
 
 
-def _df_index(df: Union[ZarrGroup, H5Group]) -> pd.Index:
+def _df_index(df: ZarrGroup | H5Group) -> pd.Index:
     index_key = df.attrs["_index"]
     return pd.Index(read_elem(df[index_key]))
 
@@ -167,9 +163,9 @@ def _df_index(df: Union[ZarrGroup, H5Group]) -> pd.Index:
 
 
 def write_concat_dense(
-    arrays: Sequence[Union[ZarrArray, H5Array]],
-    output_group: Union[ZarrGroup, H5Group],
-    output_path: Union[ZarrGroup, H5Group],
+    arrays: Sequence[ZarrArray | H5Array],
+    output_group: ZarrGroup | H5Group,
+    output_path: ZarrGroup | H5Group,
     axis: Literal[0, 1] = 0,
     reindexers: Reindexer = None,
     fill_value=None,
@@ -196,8 +192,8 @@ def write_concat_dense(
 
 def write_concat_sparse(
     datasets: Sequence[BaseCompressedSparseDataset],
-    output_group: Union[ZarrGroup, H5Group],
-    output_path: Union[ZarrGroup, H5Group],
+    output_group: ZarrGroup | H5Group,
+    output_path: ZarrGroup | H5Group,
     max_loaded_elems: int,
     axis: Literal[0, 1] = 0,
     reindexers: Reindexer = None,
@@ -235,7 +231,7 @@ def write_concat_sparse(
 
 def _write_concat_mappings(
     mappings,
-    output_group: Union[ZarrGroup, H5Group],
+    output_group: ZarrGroup | H5Group,
     keys,
     path,
     max_loaded_elems,
@@ -269,7 +265,7 @@ def _write_concat_mappings(
 
 
 def _write_concat_arrays(
-    arrays: Sequence[Union[ZarrArray, H5Array, BaseCompressedSparseDataset]],
+    arrays: Sequence[ZarrArray | H5Array | BaseCompressedSparseDataset],
     output_group,
     output_path,
     max_loaded_elems,
@@ -314,9 +310,7 @@ def _write_concat_arrays(
 
 
 def _write_concat_sequence(
-    arrays: Sequence[
-        Union[pd.DataFrame, BaseCompressedSparseDataset, H5Array, ZarrArray]
-    ],
+    arrays: Sequence[pd.DataFrame | BaseCompressedSparseDataset | H5Array | ZarrArray],
     output_group,
     output_path,
     max_loaded_elems,
@@ -401,26 +395,21 @@ def _write_dim_annot(groups, output_group, dim, concat_indices, label, label_col
 
 
 def concat_on_disk(
-    in_files: Union[
-        Collection[Union[str, os.PathLike]],
-        MutableMapping[str, Union[str, os.PathLike]],
-    ],
-    out_file: Union[str, os.PathLike],
+    in_files: Collection[str | os.PathLike] | MutableMapping[str, str | os.PathLike],
+    out_file: str | os.PathLike,
     *,
     overwrite: bool = False,
     max_loaded_elems: int = 100_000_000,
     axis: Literal[0, 1] = 0,
     join: Literal["inner", "outer"] = "inner",
-    merge: Union[
-        StrategiesLiteral, Callable[[Collection[Mapping]], Mapping], None
-    ] = None,
-    uns_merge: Union[
-        StrategiesLiteral, Callable[[Collection[Mapping]], Mapping], None
-    ] = None,
-    label: Optional[str] = None,
-    keys: Optional[Collection[str]] = None,
-    index_unique: Optional[str] = None,
-    fill_value: Optional[Any] = None,
+    merge: StrategiesLiteral | Callable[[Collection[Mapping]], Mapping] | None = None,
+    uns_merge: StrategiesLiteral
+    | Callable[[Collection[Mapping]], Mapping]
+    | None = None,
+    label: str | None = None,
+    keys: Collection[str] | None = None,
+    index_unique: str | None = None,
+    fill_value: Any | None = None,
     pairwise: bool = False,
 ) -> None:
     """Concatenates multiple AnnData objects along a specified axis using their
diff --git a/anndata/experimental/multi_files/__init__.py b/anndata/experimental/multi_files/__init__.py
index 86d4e8f44..956ebb8d2 100644
--- a/anndata/experimental/multi_files/__init__.py
+++ b/anndata/experimental/multi_files/__init__.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from ._anncollection import AnnCollection
 
 __all__ = ["AnnCollection"]
diff --git a/anndata/experimental/multi_files/_anncollection.py b/anndata/experimental/multi_files/_anncollection.py
index 8eea18b0d..390b771c7 100644
--- a/anndata/experimental/multi_files/_anncollection.py
+++ b/anndata/experimental/multi_files/_anncollection.py
@@ -1,18 +1,20 @@
-from collections.abc import Mapping
+from __future__ import annotations
+
+import warnings
+from collections.abc import Mapping, Sequence
 from functools import reduce
-from h5py import Dataset
+from typing import Callable, Literal, Union
+
 import numpy as np
 import pandas as pd
-import warnings
-
-from typing import Dict, Union, Optional, Sequence, Callable, Literal
+from h5py import Dataset
 
+from ..._core.aligned_mapping import AxisArrays
 from ..._core.anndata import AnnData
-from ..._core.index import _normalize_indices, _normalize_index, Index
-from ..._core.views import _resolve_idx
+from ..._core.index import Index, _normalize_index, _normalize_indices
 from ..._core.merge import concat_arrays, inner_concat_aligned_mapping
 from ..._core.sparse_dataset import BaseCompressedSparseDataset
-from ..._core.aligned_mapping import AxisArrays
+from ..._core.views import _resolve_idx
 
 ATTRS = ["obs", "obsm", "layers"]
 
@@ -571,8 +573,8 @@ def attrs_keys(self):
         return self.reference.attrs_keys
 
 
-DictCallable = Dict[str, Callable]
-ConvertType = Union[Callable, DictCallable, Dict[str, DictCallable]]
+DictCallable = dict[str, Callable]
+ConvertType = Union[Callable, DictCallable, dict[str, DictCallable]]
 
 
 class AnnCollection(_ConcatViewMixin, _IterateViewMixin):
@@ -665,14 +667,14 @@ class AnnCollection(_ConcatViewMixin, _IterateViewMixin):
 
     def __init__(
         self,
-        adatas: Union[Sequence[AnnData], Dict[str, AnnData]],
-        join_obs: Optional[Literal["inner", "outer"]] = "inner",
-        join_obsm: Optional[Literal["inner"]] = None,
-        join_vars: Optional[Literal["inner"]] = None,
-        label: Optional[str] = None,
-        keys: Optional[Sequence[str]] = None,
-        index_unique: Optional[str] = None,
-        convert: Optional[ConvertType] = None,
+        adatas: Sequence[AnnData] | dict[str, AnnData],
+        join_obs: Literal["inner", "outer"] | None = "inner",
+        join_obsm: Literal["inner"] | None = None,
+        join_vars: Literal["inner"] | None = None,
+        label: str | None = None,
+        keys: Sequence[str] | None = None,
+        index_unique: str | None = None,
+        convert: ConvertType | None = None,
         harmonize_dtypes: bool = True,
         indices_strict: bool = True,
     ):
@@ -933,7 +935,7 @@ def __repr__(self):
 
 
 class LazyAttrData(_IterateViewMixin):
-    def __init__(self, adset: AnnCollection, attr: str, key: Optional[str] = None):
+    def __init__(self, adset: AnnCollection, attr: str, key: str | None = None):
         self.adset = adset
         self.attr = attr
         self.key = key
diff --git a/anndata/experimental/pytorch/__init__.py b/anndata/experimental/pytorch/__init__.py
index d4fbffce7..36c9441fe 100644
--- a/anndata/experimental/pytorch/__init__.py
+++ b/anndata/experimental/pytorch/__init__.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from ._annloader import AnnLoader
 
 __all__ = ["AnnLoader"]
diff --git a/anndata/experimental/pytorch/_annloader.py b/anndata/experimental/pytorch/_annloader.py
index 15ad53a52..8cc883921 100644
--- a/anndata/experimental/pytorch/_annloader.py
+++ b/anndata/experimental/pytorch/_annloader.py
@@ -1,18 +1,22 @@
-from scipy.sparse import issparse
-from math import ceil
+from __future__ import annotations
+
 from copy import copy
 from functools import partial
-from typing import Dict, Union, Sequence
+from math import ceil
+from typing import TYPE_CHECKING
 
 import numpy as np
+from scipy.sparse import issparse
 
 from ..._core.anndata import AnnData
 from ..multi_files._anncollection import AnnCollection, _ConcatViewMixin
 
+if TYPE_CHECKING:
+    from collections.abc import Sequence
 
 try:
     import torch
-    from torch.utils.data import Sampler, BatchSampler, DataLoader
+    from torch.utils.data import BatchSampler, DataLoader, Sampler
 except ImportError:
     Sampler, BatchSampler, DataLoader = object, object, object
 
@@ -123,7 +127,7 @@ class AnnLoader(DataLoader):
 
     def __init__(
         self,
-        adatas: Union[Sequence[AnnData], Dict[str, AnnData]],
+        adatas: Sequence[AnnData] | dict[str, AnnData],
         batch_size: int = 1,
         shuffle: bool = False,
         use_default_converter: bool = True,
diff --git a/anndata/logging.py b/anndata/logging.py
index f5feac09c..a2a890c51 100644
--- a/anndata/logging.py
+++ b/anndata/logging.py
@@ -1,5 +1,7 @@
-import os
+from __future__ import annotations
+
 import logging
+import os
 
 _previous_memory_usage = None
 
diff --git a/anndata/readwrite.py b/anndata/readwrite.py
index dfe5a7074..f3d07f732 100644
--- a/anndata/readwrite.py
+++ b/anndata/readwrite.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from warnings import warn
 
 warn("Please only import from anndata, not anndata.readwrite", DeprecationWarning)
diff --git a/anndata/tests/conftest.py b/anndata/tests/conftest.py
index ef8a3b50e..e16197cc7 100644
--- a/anndata/tests/conftest.py
+++ b/anndata/tests/conftest.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import warnings
 
 import pytest
@@ -5,7 +7,6 @@
 import anndata
 from anndata.tests.helpers import subset_func  # noqa: F401
 
-
 # TODO: Should be done in pyproject.toml, see anndata/conftest.py
 warnings.filterwarnings("ignore", category=anndata.OldFormatWarning)
 
diff --git a/anndata/tests/helpers.py b/anndata/tests/helpers.py
index 450f604d9..641bdc791 100644
--- a/anndata/tests/helpers.py
+++ b/anndata/tests/helpers.py
@@ -1,34 +1,33 @@
 from __future__ import annotations
 
-from contextlib import contextmanager
-from functools import singledispatch, wraps, partial
+import random
 import re
-from string import ascii_letters
-from typing import Tuple, Optional, Type
-from collections.abc import Mapping, Collection
 import warnings
+from collections.abc import Collection, Mapping
+from contextlib import contextmanager
+from functools import partial, singledispatch, wraps
+from string import ascii_letters
 
 import h5py
 import numpy as np
 import pandas as pd
-from pandas.api.types import is_numeric_dtype
 import pytest
+from pandas.api.types import is_numeric_dtype
 from scipy import sparse
-import random
 
 from anndata import AnnData, Raw
-from anndata._core.views import ArrayView
-from anndata._core.sparse_dataset import BaseCompressedSparseDataset
 from anndata._core.aligned_mapping import AlignedMapping
-from anndata.utils import asarray
+from anndata._core.sparse_dataset import BaseCompressedSparseDataset
+from anndata._core.views import ArrayView
 from anndata.compat import (
     AwkArray,
-    DaskArray,
-    CupySparseMatrix,
     CupyArray,
     CupyCSCMatrix,
     CupyCSRMatrix,
+    CupySparseMatrix,
+    DaskArray,
 )
+from anndata.utils import asarray
 
 # Give this to gen_adata when dask array support is expected.
 GEN_ADATA_DASK_ARGS = dict(
@@ -156,24 +155,24 @@ def gen_typed_df_t2_size(m, n, index=None, columns=None) -> pd.DataFrame:
 
 # TODO: Use hypothesis for this?
 def gen_adata(
-    shape: Tuple[int, int],
+    shape: tuple[int, int],
     X_type=sparse.csr_matrix,
     X_dtype=np.float32,
     # obs_dtypes,
     # var_dtypes,
-    obsm_types: "Collection[Type]" = (
+    obsm_types: Collection[type] = (
         sparse.csr_matrix,
         np.ndarray,
         pd.DataFrame,
         AwkArray,
     ),
-    varm_types: "Collection[Type]" = (
+    varm_types: Collection[type] = (
         sparse.csr_matrix,
         np.ndarray,
         pd.DataFrame,
         AwkArray,
     ),
-    layers_types: "Collection[Type]" = (sparse.csr_matrix, np.ndarray, pd.DataFrame),
+    layers_types: Collection[type] = (sparse.csr_matrix, np.ndarray, pd.DataFrame),
     sparse_fmt: str = "csr",
 ) -> AnnData:
     """\
@@ -529,7 +528,7 @@ def assert_is_not_none(x):  # can't put an assert in a lambda
 
 @assert_equal.register(AnnData)
 def assert_adata_equal(
-    a: AnnData, b: AnnData, exact: bool = False, elem_name: Optional[str] = None
+    a: AnnData, b: AnnData, exact: bool = False, elem_name: str | None = None
 ):
     """\
     Check whether two AnnData objects are equivalent,
@@ -681,16 +680,16 @@ def as_cupy_type(val, typ=None):
             val = val.toarray()
         return cp.array(val)
     elif issubclass(typ, CupyCSRMatrix):
-        import cupyx.scipy.sparse as cpsparse
         import cupy as cp
+        import cupyx.scipy.sparse as cpsparse
 
         if isinstance(val, np.ndarray):
             return cpsparse.csr_matrix(cp.array(val))
         else:
             return cpsparse.csr_matrix(val)
     elif issubclass(typ, CupyCSCMatrix):
-        import cupyx.scipy.sparse as cpsparse
         import cupy as cp
+        import cupyx.scipy.sparse as cpsparse
 
         if isinstance(val, np.ndarray):
             return cpsparse.csc_matrix(cp.array(val))
diff --git a/anndata/tests/test_anncollection.py b/anndata/tests/test_anncollection.py
index b8def9508..aaef199e7 100644
--- a/anndata/tests/test_anncollection.py
+++ b/anndata/tests/test_anncollection.py
@@ -1,10 +1,11 @@
-import pytest
-import anndata as ad
-import numpy as np
+from __future__ import annotations
 
+import numpy as np
+import pytest
 from scipy.sparse import csr_matrix, issparse
-
 from sklearn.preprocessing import LabelEncoder
+
+import anndata as ad
 from anndata.experimental.multi_files import AnnCollection
 
 _dense = lambda a: a.toarray() if issparse(a) else a
diff --git a/anndata/tests/test_annot.py b/anndata/tests/test_annot.py
index 025c7d5a6..0ea609906 100644
--- a/anndata/tests/test_annot.py
+++ b/anndata/tests/test_annot.py
@@ -1,12 +1,13 @@
 """Test handling of values in `obs`/ `var`"""
-from natsort import natsorted
+from __future__ import annotations
+
 import numpy as np
 import pandas as pd
+import pytest
+from natsort import natsorted
 
 import anndata as ad
 
-import pytest
-
 
 @pytest.mark.parametrize("dtype", [object, "string"])
 def test_str_to_categorical(dtype):
diff --git a/anndata/tests/test_awkward.py b/anndata/tests/test_awkward.py
index 87280d5a2..993fb91de 100644
--- a/anndata/tests/test_awkward.py
+++ b/anndata/tests/test_awkward.py
@@ -1,15 +1,16 @@
 """Tests related to awkward arrays"""
-import pytest
+from __future__ import annotations
+
 import numpy as np
 import numpy.testing as npt
+import pandas as pd
+import pytest
 
-from anndata.tests.helpers import assert_equal, gen_adata, gen_awkward
+import anndata
+from anndata import AnnData, ImplicitModificationWarning, read_h5ad
 from anndata.compat import awkward as ak
-from anndata import ImplicitModificationWarning
+from anndata.tests.helpers import assert_equal, gen_adata, gen_awkward
 from anndata.utils import dim_len
-from anndata import AnnData, read_h5ad
-import anndata
-import pandas as pd
 
 
 @pytest.mark.parametrize(
diff --git a/anndata/tests/test_backed_sparse.py b/anndata/tests/test_backed_sparse.py
index 2809b7c9f..d781226ad 100644
--- a/anndata/tests/test_backed_sparse.py
+++ b/anndata/tests/test_backed_sparse.py
@@ -1,15 +1,16 @@
+from __future__ import annotations
+
 import h5py
 import numpy as np
 import pytest
+import zarr
 from scipy import sparse
 
 import anndata as ad
 from anndata._core.anndata import AnnData
 from anndata._core.sparse_dataset import sparse_dataset
-from anndata.tests.helpers import assert_equal, subset_func
 from anndata.experimental import read_dispatched
-
-import zarr
+from anndata.tests.helpers import assert_equal, subset_func
 
 subset_func2 = subset_func
 
diff --git a/anndata/tests/test_base.py b/anndata/tests/test_base.py
index 17d6a9476..14127271f 100644
--- a/anndata/tests/test_base.py
+++ b/anndata/tests/test_base.py
@@ -1,20 +1,19 @@
 from __future__ import annotations
 
-from itertools import product
 import re
 import warnings
+from itertools import product
 
 import numpy as np
-from numpy import ma
 import pandas as pd
 import pytest
+from numpy import ma
 from scipy import sparse as sp
 from scipy.sparse import csr_matrix, issparse
 
 from anndata import AnnData
 from anndata.tests.helpers import assert_equal, gen_adata
 
-
 # some test objects that we use below
 adata_dense = AnnData(np.array([[1, 2], [3, 4]]))
 adata_dense.layers["test"] = adata_dense.X
diff --git a/anndata/tests/test_concatenate.py b/anndata/tests/test_concatenate.py
index 92e8d2895..78caa8a19 100644
--- a/anndata/tests/test_concatenate.py
+++ b/anndata/tests/test_concatenate.py
@@ -1,33 +1,34 @@
+from __future__ import annotations
+
+import warnings
 from collections.abc import Hashable
 from copy import deepcopy
-from itertools import chain, product
 from functools import partial, singledispatch
-from typing import Any, List, Callable
-import warnings
+from itertools import chain, product
+from typing import Any, Callable
 
 import numpy as np
-from numpy import ma
 import pandas as pd
 import pytest
+from boltons.iterutils import default_exit, remap, research
+from numpy import ma
 from scipy import sparse
-from boltons.iterutils import research, remap, default_exit
-
 
 from anndata import AnnData, Raw, concat
-from anndata._core.index import _subset
 from anndata._core import merge
+from anndata._core.index import _subset
+from anndata.compat import AwkArray, DaskArray
 from anndata.tests import helpers
 from anndata.tests.helpers import (
-    assert_equal,
-    as_dense_dask_array,
-    gen_adata,
-    GEN_ADATA_DASK_ARGS,
     BASE_MATRIX_PARAMS,
-    DASK_MATRIX_PARAMS,
     CUPY_MATRIX_PARAMS,
+    DASK_MATRIX_PARAMS,
+    GEN_ADATA_DASK_ARGS,
+    as_dense_dask_array,
+    assert_equal,
+    gen_adata,
 )
 from anndata.utils import asarray
-from anndata.compat import DaskArray, AwkArray
 
 
 @singledispatch
@@ -963,7 +964,7 @@ def map_values(mapping, path, key, old_parent, new_parent, new_items):
     return ret
 
 
-def permute_nested_values(dicts: "List[dict]", gen_val: "Callable[[int], Any]"):
+def permute_nested_values(dicts: list[dict], gen_val: Callable[[int], Any]):
     """
     This function permutes the values of a nested mapping, for testing that out merge
     method work regardless of the values types.
@@ -1389,9 +1390,10 @@ def test_concat_X_dtype():
 
 # Tests how dask plays with other types on concatenation.
 def test_concat_different_types_dask(merge_strategy, array_type):
+    import dask.array as da
     from scipy import sparse
+
     import anndata as ad
-    import dask.array as da
 
     varm_array = sparse.random(5, 20, density=0.5, format="csr")
 
diff --git a/anndata/tests/test_concatenate_disk.py b/anndata/tests/test_concatenate_disk.py
index 1ffbb63ef..0192df452 100644
--- a/anndata/tests/test_concatenate_disk.py
+++ b/anndata/tests/test_concatenate_disk.py
@@ -1,23 +1,21 @@
-from typing import Mapping
+from __future__ import annotations
+
+from collections.abc import Mapping
 
 import numpy as np
 import pandas as pd
 import pytest
 from scipy import sparse
 
-from anndata.experimental.merge import concat_on_disk, as_group
-from anndata.experimental import write_elem, read_elem
-
 from anndata import AnnData, concat
+from anndata.experimental import read_elem, write_elem
+from anndata.experimental.merge import as_group, concat_on_disk
 from anndata.tests.helpers import (
     assert_equal,
     gen_adata,
 )
-
-
 from anndata.utils import asarray
 
-
 GEN_ADATA_OOC_CONCAT_ARGS = dict(
     obsm_types=(
         sparse.csr_matrix,
diff --git a/anndata/tests/test_dask.py b/anndata/tests/test_dask.py
index cb745a8f5..7bd353f24 100644
--- a/anndata/tests/test_dask.py
+++ b/anndata/tests/test_dask.py
@@ -1,19 +1,22 @@
 """
 For tests using dask
 """
-import anndata as ad
+from __future__ import annotations
+
 import pandas as pd
-from anndata._core.anndata import AnnData
 import pytest
+
+import anndata as ad
+from anndata._core.anndata import AnnData
+from anndata.compat import DaskArray
+from anndata.experimental import read_elem, write_elem
+from anndata.experimental.merge import as_group
 from anndata.tests.helpers import (
-    as_dense_dask_array,
     GEN_ADATA_DASK_ARGS,
-    gen_adata,
+    as_dense_dask_array,
     assert_equal,
+    gen_adata,
 )
-from anndata.experimental import write_elem, read_elem
-from anndata.experimental.merge import as_group
-from anndata.compat import DaskArray
 
 pytest.importorskip("dask.array")
 
@@ -243,6 +246,7 @@ def test_assign_X(adata):
     """Check if assignment works"""
     import dask.array as da
     import numpy as np
+
     from anndata.compat import DaskArray
 
     adata.X = da.ones(adata.X.shape)
@@ -306,8 +310,8 @@ def test_dask_to_memory_copy_unbacked():
 
 
 def test_to_memory_raw():
-    import numpy as np
     import dask.array as da
+    import numpy as np
 
     orig = gen_adata((20, 10), **GEN_ADATA_DASK_ARGS)
     orig.X = da.ones((20, 10))
@@ -327,8 +331,8 @@ def test_to_memory_raw():
 
 
 def test_to_memory_copy_raw():
-    import numpy as np
     import dask.array as da
+    import numpy as np
 
     orig = gen_adata((20, 10), **GEN_ADATA_DASK_ARGS)
     orig.X = da.ones((20, 10))
diff --git a/anndata/tests/test_dask_view_mem.py b/anndata/tests/test_dask_view_mem.py
index 6d758477b..bb758a223 100644
--- a/anndata/tests/test_dask_view_mem.py
+++ b/anndata/tests/test_dask_view_mem.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import pytest
 
 import anndata as ad
@@ -43,8 +45,8 @@ def alloc_cache():
         **{
             "layers": dict(m=da.random.random(*size)),
             "obsm": dict(m=da.random.random(*size)),
-            "obs": dict(m=da.random.random((N))),
-            "var": dict(m=da.random.random((N))),
+            "obs": dict(m=da.random.random(N)),
+            "var": dict(m=da.random.random(N)),
             "varm": dict(m=da.random.random(*size)),
         },
     )
diff --git a/anndata/tests/test_deprecations.py b/anndata/tests/test_deprecations.py
index d632e3ea2..52d6501ab 100644
--- a/anndata/tests/test_deprecations.py
+++ b/anndata/tests/test_deprecations.py
@@ -3,6 +3,8 @@
 
 This includes correct behaviour as well as throwing warnings.
 """
+from __future__ import annotations
+
 import warnings
 
 import h5py
@@ -10,9 +12,8 @@
 import pytest
 from scipy import sparse
 
-from anndata import AnnData
 import anndata as ad
-
+from anndata import AnnData
 from anndata.tests.helpers import assert_equal
 
 
@@ -101,8 +102,8 @@ def test_dtype_warning():
 def test_deprecated_write_attribute(tmp_path):
     pth = tmp_path / "file.h5"
     A = np.random.randn(20, 10)
-    from anndata._io.utils import read_attribute, write_attribute
     from anndata._io.specs import read_elem
+    from anndata._io.utils import read_attribute, write_attribute
 
     with h5py.File(pth, "w") as f:
         with pytest.warns(DeprecationWarning, match="write_elem"):
@@ -129,6 +130,7 @@ def test_deprecated_read(tmp_path):
 
 def test_deprecated_sparse_dataset_values():
     import zarr
+
     from anndata.experimental import sparse_dataset, write_elem
 
     mtx = sparse.random(50, 50, format="csr")
diff --git a/anndata/tests/test_get_vector.py b/anndata/tests/test_get_vector.py
index ca2ce18a7..baf0fd7d6 100644
--- a/anndata/tests/test_get_vector.py
+++ b/anndata/tests/test_get_vector.py
@@ -1,7 +1,9 @@
+from __future__ import annotations
+
 import numpy as np
 import pandas as pd
-from scipy import sparse
 import pytest
+from scipy import sparse
 
 import anndata as ad
 
diff --git a/anndata/tests/test_gpu.py b/anndata/tests/test_gpu.py
index 434567ca8..c6f49a696 100644
--- a/anndata/tests/test_gpu.py
+++ b/anndata/tests/test_gpu.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import pytest
 from scipy import sparse
 
@@ -16,8 +18,8 @@ def test_gpu():
 
 @pytest.mark.gpu
 def test_adata_raw_gpu():
-    from cupyx.scipy import sparse as cupy_sparse
     import cupy as cp
+    from cupyx.scipy import sparse as cupy_sparse
 
     adata = AnnData(
         X=cupy_sparse.random(500, 50, density=0.01, format="csr", dtype=cp.float32)
@@ -28,8 +30,8 @@ def test_adata_raw_gpu():
 
 @pytest.mark.gpu
 def test_raw_gpu():
-    from cupyx.scipy import sparse as cupy_sparse
     import cupy as cp
+    from cupyx.scipy import sparse as cupy_sparse
 
     adata = AnnData(
         X=cupy_sparse.random(500, 50, density=0.01, format="csr", dtype=cp.float32)
diff --git a/anndata/tests/test_hdf5_backing.py b/anndata/tests/test_hdf5_backing.py
index ab308e363..61c0c905c 100644
--- a/anndata/tests/test_hdf5_backing.py
+++ b/anndata/tests/test_hdf5_backing.py
@@ -1,16 +1,18 @@
+from __future__ import annotations
+
 from pathlib import Path
 
 import joblib
-import pytest
 import numpy as np
+import pytest
 from scipy import sparse
 
 import anndata as ad
 from anndata.tests.helpers import (
-    as_dense_dask_array,
     GEN_ADATA_DASK_ARGS,
-    gen_adata,
+    as_dense_dask_array,
     assert_equal,
+    gen_adata,
     subset_func,
 )
 from anndata.utils import asarray
diff --git a/anndata/tests/test_helpers.py b/anndata/tests/test_helpers.py
index f540c43f4..52f1d6cb1 100644
--- a/anndata/tests/test_helpers.py
+++ b/anndata/tests/test_helpers.py
@@ -1,21 +1,23 @@
+from __future__ import annotations
+
 from string import ascii_letters
 
+import numpy as np
 import pandas as pd
 import pytest
-import numpy as np
 from scipy import sparse
 
 import anndata as ad
+from anndata.compat import add_note
 from anndata.tests.helpers import (
+    asarray,
     assert_equal,
-    gen_awkward,
-    report_name,
     gen_adata,
-    asarray,
+    gen_awkward,
     pytest_8_raises,
+    report_name,
 )
 from anndata.utils import dim_len
-from anndata.compat import add_note
 
 # Testing to see if all error types can have the key name appended.
 # Currently fails for 22/118 since they have required arguments. Not sure what to do about that.
diff --git a/anndata/tests/test_inplace_subset.py b/anndata/tests/test_inplace_subset.py
index b90421965..110d2574a 100644
--- a/anndata/tests/test_inplace_subset.py
+++ b/anndata/tests/test_inplace_subset.py
@@ -1,11 +1,13 @@
+from __future__ import annotations
+
 import numpy as np
 import pytest
 from scipy import sparse
 
 from anndata.tests.helpers import (
+    as_dense_dask_array,
     assert_equal,
     gen_adata,
-    as_dense_dask_array,
 )
 from anndata.utils import asarray
 
diff --git a/anndata/tests/test_io_backwards_compat.py b/anndata/tests/test_io_backwards_compat.py
index a060d1779..fb12c8161 100644
--- a/anndata/tests/test_io_backwards_compat.py
+++ b/anndata/tests/test_io_backwards_compat.py
@@ -1,10 +1,12 @@
+from __future__ import annotations
+
 from pathlib import Path
 
+import pandas as pd
 import pytest
+from scipy import sparse
 
 import anndata as ad
-import pandas as pd
-from scipy import sparse
 from anndata.tests.helpers import assert_equal
 
 ARCHIVE_PTH = Path(__file__).parent / "data/archives"
diff --git a/anndata/tests/test_io_conversion.py b/anndata/tests/test_io_conversion.py
index dd5e9ab61..29a5d27e9 100644
--- a/anndata/tests/test_io_conversion.py
+++ b/anndata/tests/test_io_conversion.py
@@ -1,13 +1,15 @@
 """\
 This file contains tests for conversion made during io.
 """
+from __future__ import annotations
+
 import h5py
 import numpy as np
 import pytest
 from scipy import sparse
 
 import anndata as ad
-from anndata.tests.helpers import gen_adata, assert_equal
+from anndata.tests.helpers import assert_equal, gen_adata
 
 
 @pytest.fixture(
diff --git a/anndata/tests/test_io_dispatched.py b/anndata/tests/test_io_dispatched.py
index b43eb67c2..511179d4c 100644
--- a/anndata/tests/test_io_dispatched.py
+++ b/anndata/tests/test_io_dispatched.py
@@ -1,17 +1,19 @@
+from __future__ import annotations
+
 import re
 
-from scipy import sparse
 import h5py
 import zarr
+from scipy import sparse
 
 import anndata as ad
 from anndata.experimental import (
     read_dispatched,
-    write_dispatched,
     read_elem,
+    write_dispatched,
     write_elem,
 )
-from anndata.tests.helpers import gen_adata, assert_equal
+from anndata.tests.helpers import assert_equal, gen_adata
 
 
 def test_read_dispatched_w_regex():
@@ -79,7 +81,7 @@ def test_read_dispatched_null_case():
 
 
 def test_write_dispatched_chunks():
-    from itertools import repeat, chain
+    from itertools import chain, repeat
 
     def determine_chunks(elem_shape, specified_chunks):
         chunk_iterator = chain(specified_chunks, repeat(None))
diff --git a/anndata/tests/test_io_elementwise.py b/anndata/tests/test_io_elementwise.py
index 200292200..34a42e7ff 100644
--- a/anndata/tests/test_io_elementwise.py
+++ b/anndata/tests/test_io_elementwise.py
@@ -9,19 +9,18 @@
 import numpy as np
 import pandas as pd
 import pytest
-from scipy import sparse
 import zarr
+from scipy import sparse
 
 import anndata as ad
-from anndata._io.specs import _REGISTRY, get_spec, IOSpec
+from anndata._io.specs import _REGISTRY, IOSpec, get_spec, read_elem, write_elem
 from anndata._io.specs.registry import IORegistryError
-from anndata.compat import _read_attr, H5Group, ZarrGroup
-from anndata._io.specs import write_elem, read_elem
+from anndata.compat import H5Group, ZarrGroup, _read_attr
 from anndata.tests.helpers import (
-    assert_equal,
     as_cupy_type,
-    pytest_8_raises,
+    assert_equal,
     gen_adata,
+    pytest_8_raises,
 )
 
 
diff --git a/anndata/tests/test_io_partial.py b/anndata/tests/test_io_partial.py
index b75e5ccf1..d43aaca1c 100644
--- a/anndata/tests/test_io_partial.py
+++ b/anndata/tests/test_io_partial.py
@@ -1,14 +1,18 @@
+from __future__ import annotations
+
 from importlib.util import find_spec
-from anndata import AnnData
-from anndata._io.specs import read_elem
-from anndata._io.specs.registry import read_elem_partial
-from anndata._io import write_h5ad, write_zarr
-from scipy.sparse import csr_matrix
 from pathlib import Path
+
+import h5py
 import numpy as np
 import pytest
 import zarr
-import h5py
+from scipy.sparse import csr_matrix
+
+from anndata import AnnData
+from anndata._io import write_h5ad, write_zarr
+from anndata._io.specs import read_elem
+from anndata._io.specs.registry import read_elem_partial
 
 X = np.array([[1.0, 0.0, 3.0], [4.0, 0.0, 6.0], [0.0, 8.0, 0.0]], dtype="float32")
 X_check = np.array([[4.0, 0.0], [0.0, 8.0]], dtype="float32")
diff --git a/anndata/tests/test_io_utils.py b/anndata/tests/test_io_utils.py
index 8b94a5feb..c70091474 100644
--- a/anndata/tests/test_io_utils.py
+++ b/anndata/tests/test_io_utils.py
@@ -1,16 +1,18 @@
+from __future__ import annotations
+
 from contextlib import suppress
 
-import pytest
-import zarr
 import h5py
 import pandas as pd
+import pytest
+import zarr
 
 import anndata as ad
 from anndata._io.specs.registry import IORegistryError
-from anndata.compat import _clean_uns
 from anndata._io.utils import (
     report_read_key_on_error,
 )
+from anndata.compat import _clean_uns
 from anndata.experimental import read_elem, write_elem
 from anndata.tests.helpers import pytest_8_raises
 
diff --git a/anndata/tests/test_io_warnings.py b/anndata/tests/test_io_warnings.py
index 284d86ecc..dfc33ccf1 100644
--- a/anndata/tests/test_io_warnings.py
+++ b/anndata/tests/test_io_warnings.py
@@ -1,6 +1,8 @@
+from __future__ import annotations
+
+import warnings
 from importlib.util import find_spec
 from pathlib import Path
-import warnings
 
 import pytest
 
diff --git a/anndata/tests/test_layers.py b/anndata/tests/test_layers.py
index 4f9f00973..4b6a7f287 100644
--- a/anndata/tests/test_layers.py
+++ b/anndata/tests/test_layers.py
@@ -1,11 +1,13 @@
-from importlib.util import find_spec
+from __future__ import annotations
+
 import warnings
+from importlib.util import find_spec
 
-import pytest
 import numpy as np
 import pandas as pd
+import pytest
 
-from anndata import AnnData, read_loom, read_h5ad
+from anndata import AnnData, read_h5ad, read_loom
 from anndata.tests.helpers import gen_typed_df_t2_size
 
 X = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 9]])
diff --git a/anndata/tests/test_obsmvarm.py b/anndata/tests/test_obsmvarm.py
index 1c08e7545..e1e802a9d 100644
--- a/anndata/tests/test_obsmvarm.py
+++ b/anndata/tests/test_obsmvarm.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import joblib
 import numpy as np
 import pandas as pd
diff --git a/anndata/tests/test_obspvarp.py b/anndata/tests/test_obspvarp.py
index 8ff025d76..5b3e063d3 100644
--- a/anndata/tests/test_obspvarp.py
+++ b/anndata/tests/test_obspvarp.py
@@ -1,4 +1,6 @@
 # TODO: These tests should share code with test_layers, and test_obsmvarm
+from __future__ import annotations
+
 import warnings
 
 import joblib
diff --git a/anndata/tests/test_raw.py b/anndata/tests/test_raw.py
index 5686a4edc..7e4689d60 100644
--- a/anndata/tests/test_raw.py
+++ b/anndata/tests/test_raw.py
@@ -1,10 +1,11 @@
+from __future__ import annotations
+
 import numpy as np
 import pytest
 
 import anndata as ad
 from anndata._core.anndata import ImplicitModificationWarning
-from anndata.tests.helpers import assert_equal, gen_adata, GEN_ADATA_DASK_ARGS
-
+from anndata.tests.helpers import GEN_ADATA_DASK_ARGS, assert_equal, gen_adata
 
 # -------------------------------------------------------------------------------
 # Some test data
diff --git a/anndata/tests/test_readwrite.py b/anndata/tests/test_readwrite.py
index c78d3833a..98de43a61 100644
--- a/anndata/tests/test_readwrite.py
+++ b/anndata/tests/test_readwrite.py
@@ -1,29 +1,33 @@
+from __future__ import annotations
+
+import re
+import warnings
 from contextlib import contextmanager
 from importlib.util import find_spec
-from os import PathLike
 from pathlib import Path
-import re
 from string import ascii_letters
-import warnings
+from typing import TYPE_CHECKING
 
 import h5py
 import numpy as np
 import pandas as pd
 import pytest
-from scipy.sparse import csr_matrix, csc_matrix
 import zarr
+from scipy.sparse import csc_matrix, csr_matrix
 
 import anndata as ad
 from anndata._io.specs.registry import IORegistryError
-from anndata.compat import _read_attr, DaskArray
-
+from anndata.compat import DaskArray, _read_attr
 from anndata.tests.helpers import (
-    gen_adata,
-    assert_equal,
     as_dense_dask_array,
+    assert_equal,
+    gen_adata,
     pytest_8_raises,
 )
 
+if TYPE_CHECKING:
+    from os import PathLike
+
 HERE = Path(__file__).parent
 
 
@@ -481,7 +485,7 @@ def test_write_csv_view(typ, tmp_path):
 
     def md5_path(pth: PathLike) -> bytes:
         checksum = hashlib.md5()
-        with open(pth, "rb") as f:
+        with pth.open("rb") as f:
             while True:
                 buf = f.read(checksum.block_size * 100)
                 if not buf:
@@ -489,7 +493,7 @@ def md5_path(pth: PathLike) -> bytes:
                 checksum.update(buf)
         return checksum.digest()
 
-    def hash_dir_contents(dir: Path) -> "dict[str, bytes]":
+    def hash_dir_contents(dir: Path) -> dict[str, bytes]:
         root_pth = str(dir)
         return {
             str(k)[len(root_pth) :]: md5_path(k) for k in dir.rglob("*") if k.is_file()
@@ -652,7 +656,7 @@ def test_write_string_types(tmp_path, diskfmt):
     with pytest_8_raises(TypeError, match=r"writing key 'obs'") as exc_info:
         write(adata_pth)
 
-    assert str("b'c'") in str(exc_info.value)
+    assert "b'c'" in str(exc_info.value)
 
 
 @pytest.mark.parametrize(
diff --git a/anndata/tests/test_repr.py b/anndata/tests/test_repr.py
index 862b9cd65..18fffb74f 100644
--- a/anndata/tests/test_repr.py
+++ b/anndata/tests/test_repr.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import re
 from string import ascii_letters
 
diff --git a/anndata/tests/test_structured_arrays.py b/anndata/tests/test_structured_arrays.py
index 580a72554..81b6be22f 100644
--- a/anndata/tests/test_structured_arrays.py
+++ b/anndata/tests/test_structured_arrays.py
@@ -1,12 +1,13 @@
-from itertools import product, combinations
+from __future__ import annotations
+
+from itertools import combinations, product
 
 import numpy as np
 import pytest
 
-from anndata.tests.helpers import gen_vstr_recarray
-
-from anndata import AnnData
 import anndata as ad
+from anndata import AnnData
+from anndata.tests.helpers import gen_vstr_recarray
 
 
 @pytest.fixture(params=["h5ad", "zarr"])
diff --git a/anndata/tests/test_transpose.py b/anndata/tests/test_transpose.py
index e2a77dbb7..720733496 100644
--- a/anndata/tests/test_transpose.py
+++ b/anndata/tests/test_transpose.py
@@ -1,10 +1,11 @@
-from scipy import sparse
-import numpy as np
+from __future__ import annotations
 
+import numpy as np
 import pytest
+from scipy import sparse
 
 import anndata as ad
-from anndata.tests.helpers import gen_adata, assert_equal, shares_memory
+from anndata.tests.helpers import assert_equal, gen_adata, shares_memory
 
 
 def test_transpose_orig():
diff --git a/anndata/tests/test_uns.py b/anndata/tests/test_uns.py
index 013c0dea5..ef0f4f8fe 100644
--- a/anndata/tests/test_uns.py
+++ b/anndata/tests/test_uns.py
@@ -1,6 +1,7 @@
+from __future__ import annotations
+
 import numpy as np
 import pandas as pd
-
 import pytest
 
 from anndata import AnnData
diff --git a/anndata/tests/test_utils.py b/anndata/tests/test_utils.py
index 7d766f304..f57fc5d6e 100644
--- a/anndata/tests/test_utils.py
+++ b/anndata/tests/test_utils.py
@@ -1,11 +1,14 @@
-import pandas as pd
-from scipy import sparse
+from __future__ import annotations
+
 from itertools import repeat
+
+import pandas as pd
 import pytest
+from scipy import sparse
 
 import anndata as ad
-from anndata.utils import make_index_unique
 from anndata.tests.helpers import gen_typed_df
+from anndata.utils import make_index_unique
 
 
 def test_make_index_unique():
diff --git a/anndata/tests/test_views.py b/anndata/tests/test_views.py
index ff9a67746..b195c13b4 100644
--- a/anndata/tests/test_views.py
+++ b/anndata/tests/test_views.py
@@ -1,30 +1,31 @@
+from __future__ import annotations
+
 from copy import deepcopy
 from operator import mul
 
 import joblib
 import numpy as np
-from scipy import sparse
 import pandas as pd
 import pytest
+from dask.base import normalize_token, tokenize
+from scipy import sparse
 
 import anndata as ad
 from anndata._core.index import _normalize_index
-from anndata._core.views import ArrayView, SparseCSRView, SparseCSCView
+from anndata._core.views import ArrayView, SparseCSCView, SparseCSRView
 from anndata.compat import CupyCSCMatrix, DaskArray
-from anndata.utils import asarray
 from anndata.tests.helpers import (
-    gen_adata,
-    subset_func,
-    slice_subset,
-    single_subset,
-    assert_equal,
-    GEN_ADATA_DASK_ARGS,
     BASE_MATRIX_PARAMS,
-    DASK_MATRIX_PARAMS,
     CUPY_MATRIX_PARAMS,
+    DASK_MATRIX_PARAMS,
+    GEN_ADATA_DASK_ARGS,
+    assert_equal,
+    gen_adata,
+    single_subset,
+    slice_subset,
+    subset_func,
 )
-from dask.base import tokenize, normalize_token
-
+from anndata.utils import asarray
 
 # ------------------------------------------------------------------------------
 # Some test data
@@ -343,11 +344,11 @@ def test_set_scalar_subset_X(matrix_type, subset_func):
     if isinstance(adata.X, CupyCSCMatrix):
         # Comparison broken for CSC matrices
         # https://github.com/cupy/cupy/issues/7757
-        assert asarray((orig_X_val.tocsr() != adata.X.tocsr())).sum() == mul(
+        assert asarray(orig_X_val.tocsr() != adata.X.tocsr()).sum() == mul(
             *adata_subset.shape
         )
     else:
-        assert asarray((orig_X_val != adata.X)).sum() == mul(*adata_subset.shape)
+        assert asarray(orig_X_val != adata.X).sum() == mul(*adata_subset.shape)
 
 
 # TODO: Use different kind of subsetting for adata and view
diff --git a/anndata/tests/test_x.py b/anndata/tests/test_x.py
index 9ec8800e6..5f381c8c1 100644
--- a/anndata/tests/test_x.py
+++ b/anndata/tests/test_x.py
@@ -1,16 +1,16 @@
 """Tests for the attribute .X"""
+from __future__ import annotations
+
 import numpy as np
 import pandas as pd
+import pytest
 from scipy import sparse
 
 import anndata as ad
 from anndata import AnnData
+from anndata.tests.helpers import assert_equal, gen_adata
 from anndata.utils import asarray
 
-import pytest
-
-from anndata.tests.helpers import gen_adata, assert_equal
-
 UNLABELLED_ARRAY_TYPES = [
     pytest.param(sparse.csr_matrix, id="csr"),
     pytest.param(sparse.csc_matrix, id="csc"),
diff --git a/anndata/utils.py b/anndata/utils.py
index 375bdf208..b5fc5c16c 100644
--- a/anndata/utils.py
+++ b/anndata/utils.py
@@ -1,16 +1,20 @@
+from __future__ import annotations
+
 import warnings
-from functools import wraps, singledispatch
-from typing import Mapping, Any, Sequence, Union
+from functools import singledispatch, wraps
+from typing import TYPE_CHECKING, Any
 
 import h5py
-import pandas as pd
 import numpy as np
+import pandas as pd
 from scipy import sparse
 
-from .logging import get_logger
-
 from ._core.sparse_dataset import BaseCompressedSparseDataset
 from .compat import CupyArray, CupySparseMatrix, DaskArray
+from .logging import get_logger
+
+if TYPE_CHECKING:
+    from collections.abc import Mapping, Sequence
 
 logger = get_logger(__name__)
 
@@ -259,7 +263,7 @@ def warn_names_duplicates(attr: str):
 
 def ensure_df_homogeneous(
     df: pd.DataFrame, name: str
-) -> Union[np.ndarray, sparse.csr_matrix]:
+) -> np.ndarray | sparse.csr_matrix:
     # TODO: rename this function, I would not expect this to return a non-dataframe
     if all(isinstance(dt, pd.SparseDtype) for dt in df.dtypes):
         arr = df.sparse.to_coo().tocsr()
diff --git a/benchmarks/benchmarks/readwrite.py b/benchmarks/benchmarks/readwrite.py
index 8d9b88e81..c273a436b 100644
--- a/benchmarks/benchmarks/readwrite.py
+++ b/benchmarks/benchmarks/readwrite.py
@@ -19,20 +19,20 @@
 * io for backed objects
 * Reading dense as sparse, writing sparse as dense
 """
+from __future__ import annotations
+
+import sys
 import tempfile
 from pathlib import Path
-import sys
 
-from memory_profiler import memory_usage
 import numpy as np
 import pooch
-
-from .utils import sedate, get_peak_mem, get_actualsize
+from memory_profiler import memory_usage
 
 # from . import datasets
-
 import anndata
 
+from .utils import get_actualsize, get_peak_mem, sedate
 
 PBMC_3K_URL = "http://falexwolf.de/data/pbmc3k_raw.h5ad"
 
diff --git a/benchmarks/benchmarks/utils.py b/benchmarks/benchmarks/utils.py
index 75fd4505e..05438811d 100644
--- a/benchmarks/benchmarks/utils.py
+++ b/benchmarks/benchmarks/utils.py
@@ -1,12 +1,14 @@
+from __future__ import annotations
+
+import gc
+import sys
 from string import ascii_lowercase
 from time import sleep
 
-from memory_profiler import memory_usage
 import numpy as np
 import pandas as pd
+from memory_profiler import memory_usage
 from scipy import sparse
-import sys
-import gc
 
 from anndata import AnnData
 
@@ -121,10 +123,10 @@ def gen_adata(n_obs, n_var, attr_set):
     if "obs,var" in attr_set:
         adata.obs = pd.DataFrame(
             {k: np.random.randint(0, 100, n_obs) for k in ascii_lowercase},
-            index=["cell{}".format(i) for i in range(n_obs)],
+            index=[f"cell{i}" for i in range(n_obs)],
         )
         adata.var = pd.DataFrame(
             {k: np.random.randint(0, 100, n_var) for k in ascii_lowercase},
-            index=["gene{}".format(i) for i in range(n_var)],
+            index=[f"gene{i}" for i in range(n_var)],
         )
     return adata
diff --git a/conftest.py b/conftest.py
index fe4dace31..1825ef24c 100644
--- a/conftest.py
+++ b/conftest.py
@@ -2,13 +2,16 @@
 # 1. to allow ignoring warnings without test collection failing on CI
 # 2. as a pytest plugin/config that applies to doctests as well
 # TODO: Fix that, e.g. with the `pytest -p anndata.testing._pytest` pattern.
+from __future__ import annotations
 
-from pathlib import Path
+from typing import TYPE_CHECKING
 
 import pytest
 
 from anndata.compat import chdir
 
+if TYPE_CHECKING:
+    from pathlib import Path
 
 doctest_marker = pytest.mark.usefixtures("doctest_env")
 
diff --git a/docs/conf.py b/docs/conf.py
index 0e2c3f96a..a25b0f6cf 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -1,9 +1,13 @@
+from __future__ import annotations
+
 import sys
-from pathlib import Path
 from datetime import datetime
 from importlib import metadata
+from pathlib import Path
+from typing import TYPE_CHECKING
 
-from sphinx.application import Sphinx
+if TYPE_CHECKING:
+    from sphinx.application import Sphinx
 
 HERE = Path(__file__).parent
 sys.path[:0] = [str(HERE / "extensions")]
diff --git a/docs/release-notes/0.10.0.md b/docs/release-notes/0.10.0.md
index c60f548ab..871be24d7 100644
--- a/docs/release-notes/0.10.0.md
+++ b/docs/release-notes/0.10.0.md
@@ -31,6 +31,8 @@
 ```{rubric} Other updates
 ```
 
+- Bump minimum python version to 3.9 {pr}`1117` {user}`flying-sheep`
+
 ```{rubric} Deprecations
 ```
 
diff --git a/pyproject.toml b/pyproject.toml
index 41682d2aa..e375d4700 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -5,18 +5,18 @@ requires = ["hatchling", "hatch-vcs"]
 [project]
 name = "anndata"
 description = "Annotated data."
-requires-python = ">=3.8"
+requires-python = ">=3.9"
 license = "BSD-3-Clause"
 authors = [
-    {name = "Philipp Angerer"},
-    {name = "Alex Wolf"},
-    {name = "Isaac Virshup"},
-    {name = "Sergei Rybakov"},
+    { name = "Philipp Angerer" },
+    { name = "Alex Wolf" },
+    { name = "Isaac Virshup" },
+    { name = "Sergei Rybakov" },
 ]
 maintainers = [
-    {name = "Isaac Virshup", email = "ivirshup@gmail.com"},
-    {name = "Philipp Angerer", email = "philipp.angerer@helmholtz-munich.de"},
-    {name = "Alex Wolf", email = "f.alex.wolf@gmx.de"},
+    { name = "Isaac Virshup", email = "ivirshup@gmail.com" },
+    { name = "Philipp Angerer", email = "philipp.angerer@helmholtz-munich.de" },
+    { name = "Alex Wolf", email = "f.alex.wolf@gmx.de" },
 ]
 readme = "README.md"
 classifiers = [
@@ -29,7 +29,6 @@ classifiers = [
     "Operating System :: Microsoft :: Windows",
     "Operating System :: POSIX :: Linux",
     "Programming Language :: Python :: 3",
-    "Programming Language :: Python :: 3.8",
     "Programming Language :: Python :: 3.9",
     "Programming Language :: Python :: 3.10",
     "Programming Language :: Python :: 3.11",
@@ -40,7 +39,7 @@ dependencies = [
     # pandas <1.1.1 has pandas/issues/35446
     # pandas 2.1.0rc0 has pandas/issues/54622
     "pandas >=1.1.1, !=2.1.0rc0",
-    "numpy>=1.16.5",  # required by pandas 1.x
+    "numpy>=1.16.5",                         # required by pandas 1.x
     "scipy>1.4",
     "h5py>=3",
     "exceptiongroup; python_version<'3.11'",
@@ -74,7 +73,7 @@ doc = [
     "scanpydoc>=0.9",
     "zarr",
     "awkward>=2.0.7",
-    "IPython", # For syntax highlighting in notebooks
+    "IPython",                          # For syntax highlighting in notebooks
     "myst_parser",
 ]
 test = [
@@ -92,15 +91,10 @@ test = [
     "awkward>=2.3",
     "pytest_memray",
 ]
-gpu = [
-    "cupy",
-]
+gpu = ["cupy"]
 
 [tool.hatch.build]
-exclude = [
-    "anndata/tests/test_*.py",
-    "anndata/tests/data",
-]
+exclude = ["anndata/tests/test_*.py", "anndata/tests/data"]
 [tool.hatch.version]
 source = "vcs"
 [tool.hatch.build.hooks.vcs]
@@ -108,20 +102,13 @@ version-file = "anndata/_version.py"
 
 [tool.coverage.run]
 source = ["anndata"]
-omit = [
-	"setup.py",
-	"versioneer.py",
-	"anndata/_version.py",
-	"**/test_*.py",
-]
+omit = ["setup.py", "versioneer.py", "anndata/_version.py", "**/test_*.py"]
 
 [tool.pytest.ini_options]
 addopts = "--doctest-modules"
 python_files = "test_*.py"
 testpaths = ["anndata", "docs/concatenation.rst"]
-filterwarnings = [
-    'ignore:X\.dtype being converted to np.float32:FutureWarning'
-]
+filterwarnings = ['ignore:X\.dtype being converted to np.float32:FutureWarning']
 # For some reason this effects how logging is shown when tests are run
 xfail_strict = true
 markers = ["gpu: mark test to run on GPU"]
@@ -130,19 +117,27 @@ markers = ["gpu: mark test to run on GPU"]
 ignore = [
     # line too long -> we accept long comment lines; black gets rid of long code lines
     "E501",
-    # Do not assign a lambda expression, use a def -> Scanpy allows lambda expression assignments,
+    # Do not assign a lambda expression, use a def -> AnnData allows lambda expression assignments,
     "E731",
     # allow I, O, l as variable names -> I is the identity matrix, i, j, k, l is reasonable indexing notation
     "E741",
 ]
 select = [
-    "E",
-    "F",
-    "W",
+    "E",   # Error detected by Pycodestyle
+    "F",   # Errors detected by Pyflakes
+    "W",   # Warning detected by Pycodestyle
+    "UP",  # pyupgrade
+    "I",   # isort
+    "TCH", # manage type checking blocks
+    "ICN", # Follow import conventions
+    "PTH", # Pathlib instead of os.path
 ]
 [tool.ruff.per-file-ignores]
 # E721 comparing types, but we specifically are checking that we aren't getting subtypes (views)
 "anndata/tests/test_readwrite.py" = ["E721"]
+[tool.ruff.isort]
+known-first-party = ["anndata"]
+required-imports = ["from __future__ import annotations"]
 
 [tool.codespell]
 skip = ".git,*.pdf,*.svg"