diff --git a/.flake8 b/.flake8
index 3d2d0193a83a..3a65b6b2c583 100644
--- a/.flake8
+++ b/.flake8
@@ -18,20 +18,15 @@
 #     F403   import *' used; unable to detect undefined names
 #     F405   defined from star imports
 
-# Rules that we'd like to enable in the future:
-#     Y037   Use PEP 604 syntax instead of `typing.Union` and `typing.Optional`.
-#            Currently can't be enabled due to a few lingering bugs in mypy regarding
-#            PEP 604 type aliases (see #4819).
-
 [flake8]
 per-file-ignores =
   *.py: E203, E301, E302, E305, E501
-  *.pyi: B, E301, E302, E305, E501, E701, E741, F401, F403, F405, F822, Y037
+  *.pyi: B, E301, E302, E305, E501, E701, E741, F401, F403, F405, F822
   # Since typing.pyi defines "overload" this is not recognized by flake8 as typing.overload.
   # Unfortunately, flake8 does not allow to "noqa" just a specific error inside the file itself.
   # https://github.com/PyCQA/flake8/issues/1079
   #     F811 redefinition of unused '...'
-  stdlib/typing.pyi: B, E301, E302, E305, E501, E701, E741, F401, F403, F405, F811, F822, Y037
+  stdlib/typing.pyi: B, E301, E302, E305, E501, E701, E741, F401, F403, F405, F811, F822
   # Generated protobuf files include docstrings
   *_pb2.pyi: B, E301, E302, E305, E501, E701, Y021, Y026
 
diff --git a/stdlib/_csv.pyi b/stdlib/_csv.pyi
index 7d15365d3b02..c3f1dd58cd3c 100644
--- a/stdlib/_csv.pyi
+++ b/stdlib/_csv.pyi
@@ -1,6 +1,6 @@
 from _typeshed import SupportsWrite
 from collections.abc import Iterable, Iterator
-from typing import Any, Union
+from typing import Any
 from typing_extensions import Literal, TypeAlias
 
 __version__: str
@@ -27,7 +27,7 @@ class Dialect:
     strict: bool
     def __init__(self) -> None: ...
 
-_DialectLike: TypeAlias = Union[str, Dialect, type[Dialect]]
+_DialectLike: TypeAlias = str | Dialect | type[Dialect]
 
 class _reader(Iterator[list[str]]):
     @property
diff --git a/stdlib/_decimal.pyi b/stdlib/_decimal.pyi
index 38b8ac30cc2f..5924c36a37ff 100644
--- a/stdlib/_decimal.pyi
+++ b/stdlib/_decimal.pyi
@@ -3,11 +3,11 @@ import sys
 from _typeshed import Self
 from collections.abc import Container, Sequence
 from types import TracebackType
-from typing import Any, ClassVar, NamedTuple, Union, overload
+from typing import Any, ClassVar, NamedTuple, overload
 from typing_extensions import Literal, TypeAlias
 
 _Decimal: TypeAlias = Decimal | int
-_DecimalNew: TypeAlias = Union[Decimal, float, str, tuple[int, Sequence[int], int]]
+_DecimalNew: TypeAlias = Decimal | float | str | tuple[int, Sequence[int], int]
 _ComparableNum: TypeAlias = Decimal | float | numbers.Rational
 
 __version__: str
diff --git a/stdlib/_typeshed/__init__.pyi b/stdlib/_typeshed/__init__.pyi
index 33af534311d1..d0c6b3ab1173 100644
--- a/stdlib/_typeshed/__init__.pyi
+++ b/stdlib/_typeshed/__init__.pyi
@@ -11,7 +11,7 @@ from collections.abc import Awaitable, Callable, Iterable, Set as AbstractSet
 from dataclasses import Field
 from os import PathLike
 from types import FrameType, TracebackType
-from typing import Any, AnyStr, ClassVar, Generic, Protocol, TypeVar, Union
+from typing import Any, AnyStr, ClassVar, Generic, Protocol, TypeVar
 from typing_extensions import Final, Literal, LiteralString, TypeAlias, final
 
 _KT = TypeVar("_KT")
@@ -265,7 +265,7 @@ IndexableBuffer: TypeAlias = bytes | bytearray | memoryview | array.array[Any] |
 #     def __buffer__(self, __flags: int) -> memoryview: ...
 
 ExcInfo: TypeAlias = tuple[type[BaseException], BaseException, TracebackType]
-OptExcInfo: TypeAlias = Union[ExcInfo, tuple[None, None, None]]
+OptExcInfo: TypeAlias = ExcInfo | tuple[None, None, None]
 
 # stable
 if sys.version_info >= (3, 10):
diff --git a/stdlib/copyreg.pyi b/stdlib/copyreg.pyi
index 07338b422385..8f7fd957fc52 100644
--- a/stdlib/copyreg.pyi
+++ b/stdlib/copyreg.pyi
@@ -1,9 +1,9 @@
 from collections.abc import Callable, Hashable
-from typing import Any, SupportsInt, TypeVar, Union
+from typing import Any, SupportsInt, TypeVar
 from typing_extensions import TypeAlias
 
 _T = TypeVar("_T")
-_Reduce: TypeAlias = Union[tuple[Callable[..., _T], tuple[Any, ...]], tuple[Callable[..., _T], tuple[Any, ...], Any | None]]
+_Reduce: TypeAlias = tuple[Callable[..., _T], tuple[Any, ...]] | tuple[Callable[..., _T], tuple[Any, ...], Any | None]
 
 __all__ = ["pickle", "constructor", "add_extension", "remove_extension", "clear_extension_cache"]
 
diff --git a/stdlib/ctypes/__init__.pyi b/stdlib/ctypes/__init__.pyi
index cd31a36a354d..87ae2513e1e7 100644
--- a/stdlib/ctypes/__init__.pyi
+++ b/stdlib/ctypes/__init__.pyi
@@ -3,7 +3,7 @@ from _ctypes import RTLD_GLOBAL as RTLD_GLOBAL, RTLD_LOCAL as RTLD_LOCAL
 from _typeshed import ReadableBuffer, Self, WriteableBuffer
 from abc import abstractmethod
 from collections.abc import Callable, Iterable, Iterator, Mapping, Sequence
-from typing import Any, ClassVar, Generic, TypeVar, Union as _UnionT, overload
+from typing import Any, ClassVar, Generic, TypeVar, overload
 from typing_extensions import TypeAlias
 
 if sys.version_info >= (3, 9):
@@ -91,7 +91,7 @@ class _CanCastTo(_CData): ...
 class _PointerLike(_CanCastTo): ...
 
 _ECT: TypeAlias = Callable[[type[_CData] | None, _FuncPointer, tuple[_CData, ...]], _CData]
-_PF: TypeAlias = _UnionT[tuple[int], tuple[int, str], tuple[int, str, Any]]
+_PF: TypeAlias = tuple[int] | tuple[int, str] | tuple[int, str, Any]
 
 class _FuncPointer(_PointerLike, _CData):
     restype: type[_CData] | Callable[[int], Any] | None
diff --git a/stdlib/distutils/ccompiler.pyi b/stdlib/distutils/ccompiler.pyi
index 711b30ba4e0e..e7277aa3f9c4 100644
--- a/stdlib/distutils/ccompiler.pyi
+++ b/stdlib/distutils/ccompiler.pyi
@@ -1,8 +1,8 @@
 from collections.abc import Callable
-from typing import Any, Union
+from typing import Any
 from typing_extensions import TypeAlias
 
-_Macro: TypeAlias = Union[tuple[str], tuple[str, str | None]]
+_Macro: TypeAlias = tuple[str] | tuple[str, str | None]
 
 def gen_lib_options(
     compiler: CCompiler, library_dirs: list[str], runtime_library_dirs: list[str], libraries: list[str]
diff --git a/stdlib/email/__init__.pyi b/stdlib/email/__init__.pyi
index 6b59dc73d5cc..fca302f5f1a7 100644
--- a/stdlib/email/__init__.pyi
+++ b/stdlib/email/__init__.pyi
@@ -1,12 +1,12 @@
 from collections.abc import Callable
 from email.message import Message
 from email.policy import Policy
-from typing import IO, Union
+from typing import IO
 from typing_extensions import TypeAlias
 
 # Definitions imported by multiple submodules in typeshed
-_ParamType: TypeAlias = Union[str, tuple[str | None, str | None, str]]  # noqa: Y047
-_ParamsType: TypeAlias = Union[str, None, tuple[str, str | None, str]]  # noqa: Y047
+_ParamType: TypeAlias = str | tuple[str | None, str | None, str]  # noqa: Y047
+_ParamsType: TypeAlias = str | None | tuple[str, str | None, str]  # noqa: Y047
 
 def message_from_string(s: str, _class: Callable[[], Message] = ..., *, policy: Policy = ...) -> Message: ...
 def message_from_bytes(s: bytes | bytearray, _class: Callable[[], Message] = ..., *, policy: Policy = ...) -> Message: ...
diff --git a/stdlib/inspect.pyi b/stdlib/inspect.pyi
index 3b82e0b0af2a..5fa806bca988 100644
--- a/stdlib/inspect.pyi
+++ b/stdlib/inspect.pyi
@@ -25,7 +25,7 @@ from types import (
     TracebackType,
     WrapperDescriptorType,
 )
-from typing import Any, ClassVar, NamedTuple, Protocol, TypeVar, Union, overload
+from typing import Any, ClassVar, NamedTuple, Protocol, TypeVar, overload
 from typing_extensions import Literal, ParamSpec, TypeAlias, TypeGuard
 
 if sys.version_info >= (3, 11):
@@ -264,9 +264,9 @@ def isdatadescriptor(object: object) -> TypeGuard[_SupportsSet[Any, Any] | _Supp
 #
 # Retrieving source code
 #
-_SourceObjectType: TypeAlias = Union[
-    ModuleType, type[Any], MethodType, FunctionType, TracebackType, FrameType, CodeType, Callable[..., Any]
-]
+_SourceObjectType: TypeAlias = (
+    ModuleType | type[Any] | MethodType | FunctionType | TracebackType | FrameType | CodeType | Callable[..., Any]
+)
 
 def findsource(object: _SourceObjectType) -> tuple[list[str], int]: ...
 def getabsfile(object: _SourceObjectType, _filename: str | None = None) -> str: ...
diff --git a/stdlib/logging/__init__.pyi b/stdlib/logging/__init__.pyi
index 231700653a32..b68eb201df40 100644
--- a/stdlib/logging/__init__.pyi
+++ b/stdlib/logging/__init__.pyi
@@ -7,7 +7,7 @@ from re import Pattern
 from string import Template
 from time import struct_time
 from types import FrameType, TracebackType
-from typing import Any, ClassVar, Generic, TextIO, TypeVar, Union, overload
+from typing import Any, ClassVar, Generic, TextIO, TypeVar, overload
 from typing_extensions import Literal, TypeAlias
 
 if sys.version_info >= (3, 11):
@@ -61,7 +61,7 @@ __all__ = [
 if sys.version_info >= (3, 11):
     __all__ += ["getLevelNamesMapping"]
 
-_SysExcInfoType: TypeAlias = Union[tuple[type[BaseException], BaseException, TracebackType | None], tuple[None, None, None]]
+_SysExcInfoType: TypeAlias = tuple[type[BaseException], BaseException, TracebackType | None] | tuple[None, None, None]
 _ExcInfoType: TypeAlias = None | bool | _SysExcInfoType | BaseException
 _ArgsType: TypeAlias = tuple[object, ...] | Mapping[str, object]
 _FilterType: TypeAlias = Filter | Callable[[LogRecord], bool]
diff --git a/stdlib/marshal.pyi b/stdlib/marshal.pyi
index da5d1a95a6f6..21f05c908479 100644
--- a/stdlib/marshal.pyi
+++ b/stdlib/marshal.pyi
@@ -1,31 +1,31 @@
 import builtins
 import types
 from _typeshed import ReadableBuffer, SupportsRead, SupportsWrite
-from typing import Any, Union
+from typing import Any
 from typing_extensions import TypeAlias
 
 version: int
 
-_Marshallable: TypeAlias = Union[
+_Marshallable: TypeAlias = (
     # handled in w_object() in marshal.c
-    None,
-    type[StopIteration],
-    builtins.ellipsis,
-    bool,
+    None
+    | type[StopIteration]
+    | builtins.ellipsis
+    | bool
     # handled in w_complex_object() in marshal.c
-    int,
-    float,
-    complex,
-    bytes,
-    str,
-    tuple[_Marshallable, ...],
-    list[Any],
-    dict[Any, Any],
-    set[Any],
-    frozenset[_Marshallable],
-    types.CodeType,
-    ReadableBuffer,
-]
+    | int
+    | float
+    | complex
+    | bytes
+    | str
+    | tuple[_Marshallable, ...]
+    | list[Any]
+    | dict[Any, Any]
+    | set[Any]
+    | frozenset[_Marshallable]
+    | types.CodeType
+    | ReadableBuffer
+)
 
 def dump(__value: _Marshallable, __file: SupportsWrite[bytes], __version: int = 4) -> None: ...
 def load(__file: SupportsRead[bytes]) -> Any: ...
diff --git a/stdlib/multiprocessing/connection.pyi b/stdlib/multiprocessing/connection.pyi
index 392e3168aaaa..868921f8b1d2 100644
--- a/stdlib/multiprocessing/connection.pyi
+++ b/stdlib/multiprocessing/connection.pyi
@@ -3,13 +3,13 @@ import sys
 import types
 from _typeshed import ReadableBuffer, Self
 from collections.abc import Iterable
-from typing import Any, Union
+from typing import Any
 from typing_extensions import SupportsIndex, TypeAlias
 
 __all__ = ["Client", "Listener", "Pipe", "wait"]
 
 # https://docs.python.org/3/library/multiprocessing.html#address-formats
-_Address: TypeAlias = Union[str, tuple[str, int]]
+_Address: TypeAlias = str | tuple[str, int]
 
 class _ConnectionBase:
     def __init__(self, handle: SupportsIndex, readable: bool = True, writable: bool = True) -> None: ...
diff --git a/stdlib/multiprocessing/dummy/connection.pyi b/stdlib/multiprocessing/dummy/connection.pyi
index 1630472b3b06..82a9027141fa 100644
--- a/stdlib/multiprocessing/dummy/connection.pyi
+++ b/stdlib/multiprocessing/dummy/connection.pyi
@@ -1,14 +1,14 @@
 from _typeshed import Self
 from queue import Queue
 from types import TracebackType
-from typing import Any, Union
+from typing import Any
 from typing_extensions import TypeAlias
 
 __all__ = ["Client", "Listener", "Pipe"]
 
 families: list[None]
 
-_Address: TypeAlias = Union[str, tuple[str, int]]
+_Address: TypeAlias = str | tuple[str, int]
 
 class Connection:
     _in: Any
diff --git a/stdlib/pickle.pyi b/stdlib/pickle.pyi
index dc098cae97b7..57c4cb03e484 100644
--- a/stdlib/pickle.pyi
+++ b/stdlib/pickle.pyi
@@ -1,7 +1,7 @@
 import sys
 from _typeshed import ReadableBuffer, SupportsWrite
 from collections.abc import Callable, Iterable, Iterator, Mapping
-from typing import Any, ClassVar, Protocol, SupportsBytes, Union
+from typing import Any, ClassVar, Protocol, SupportsBytes
 from typing_extensions import SupportsIndex, TypeAlias, final
 
 __all__ = [
@@ -142,13 +142,13 @@ class PickleError(Exception): ...
 class PicklingError(PickleError): ...
 class UnpicklingError(PickleError): ...
 
-_ReducedType: TypeAlias = Union[
-    str,
-    tuple[Callable[..., Any], tuple[Any, ...]],
-    tuple[Callable[..., Any], tuple[Any, ...], Any],
-    tuple[Callable[..., Any], tuple[Any, ...], Any, Iterator[Any] | None],
-    tuple[Callable[..., Any], tuple[Any, ...], Any, Iterator[Any] | None, Iterator[Any] | None],
-]
+_ReducedType: TypeAlias = (
+    str
+    | tuple[Callable[..., Any], tuple[Any, ...]]
+    | tuple[Callable[..., Any], tuple[Any, ...], Any]
+    | tuple[Callable[..., Any], tuple[Any, ...], Any, Iterator[Any] | None]
+    | tuple[Callable[..., Any], tuple[Any, ...], Any, Iterator[Any] | None, Iterator[Any] | None]
+)
 
 class Pickler:
     fast: bool
diff --git a/stdlib/signal.pyi b/stdlib/signal.pyi
index d1bd6930626c..29481119ba73 100644
--- a/stdlib/signal.pyi
+++ b/stdlib/signal.pyi
@@ -3,7 +3,7 @@ from _typeshed import structseq
 from collections.abc import Callable, Iterable
 from enum import IntEnum
 from types import FrameType
-from typing import Any, Union
+from typing import Any
 from typing_extensions import Final, Never, TypeAlias, final
 
 NSIG: int
@@ -62,7 +62,7 @@ SIG_DFL: Handlers
 SIG_IGN: Handlers
 
 _SIGNUM: TypeAlias = int | Signals
-_HANDLER: TypeAlias = Union[Callable[[int, FrameType | None], Any], int, Handlers, None]
+_HANDLER: TypeAlias = Callable[[int, FrameType | None], Any] | int | Handlers | None
 
 def default_int_handler(__signalnum: int, __frame: FrameType | None) -> Never: ...
 
diff --git a/stdlib/socketserver.pyi b/stdlib/socketserver.pyi
index b35f1553fb44..c74312cea6e6 100644
--- a/stdlib/socketserver.pyi
+++ b/stdlib/socketserver.pyi
@@ -4,7 +4,7 @@ from _socket import _Address, _RetAddress
 from _typeshed import ReadableBuffer, Self
 from collections.abc import Callable
 from socket import socket as _socket
-from typing import Any, BinaryIO, ClassVar, Union
+from typing import Any, BinaryIO, ClassVar
 from typing_extensions import TypeAlias
 
 __all__ = [
@@ -29,7 +29,7 @@ if sys.platform != "win32":
         "UnixStreamServer",
     ]
 
-_RequestType: TypeAlias = Union[_socket, tuple[bytes, _socket]]
+_RequestType: TypeAlias = _socket | tuple[bytes, _socket]
 _AfUnixAddress: TypeAlias = str | ReadableBuffer  # adddress acceptable for an AF_UNIX socket
 _AfInetAddress: TypeAlias = tuple[str | bytes | bytearray, int]  # address acceptable for an AF_INET socket
 
diff --git a/stdlib/ssl.pyi b/stdlib/ssl.pyi
index f8b97fb60eb7..73df70c00d3c 100644
--- a/stdlib/ssl.pyi
+++ b/stdlib/ssl.pyi
@@ -3,7 +3,7 @@ import socket
 import sys
 from _typeshed import ReadableBuffer, Self, StrOrBytesPath, WriteableBuffer
 from collections.abc import Callable, Iterable
-from typing import Any, NamedTuple, Union, overload
+from typing import Any, NamedTuple, overload
 from typing_extensions import Literal, TypeAlias, TypedDict, final
 
 _PCTRTT: TypeAlias = tuple[tuple[str, str], ...]
@@ -11,7 +11,7 @@ _PCTRTTT: TypeAlias = tuple[_PCTRTT, ...]
 _PeerCertRetDictType: TypeAlias = dict[str, str | _PCTRTTT | _PCTRTT]
 _PeerCertRetType: TypeAlias = _PeerCertRetDictType | bytes | None
 _EnumRetType: TypeAlias = list[tuple[bytes, str, set[str] | bool]]
-_PasswordType: TypeAlias = Union[Callable[[], str | bytes | bytearray], str, bytes, bytearray]
+_PasswordType: TypeAlias = Callable[[], str | bytes | bytearray] | str | bytes | bytearray
 
 _SrvnmeCbType: TypeAlias = Callable[[SSLSocket | SSLObject, str | None, SSLSocket], int | None]
 
diff --git a/stdlib/tkinter/__init__.pyi b/stdlib/tkinter/__init__.pyi
index 4aab7da1a690..1d30e4b73c23 100644
--- a/stdlib/tkinter/__init__.pyi
+++ b/stdlib/tkinter/__init__.pyi
@@ -6,7 +6,7 @@ from enum import Enum
 from tkinter.constants import *
 from tkinter.font import _FontDescription
 from types import TracebackType
-from typing import Any, Generic, NamedTuple, Protocol, TypeVar, Union, overload
+from typing import Any, Generic, NamedTuple, Protocol, TypeVar, overload
 from typing_extensions import Literal, TypeAlias, TypedDict
 
 if sys.version_info >= (3, 9):
@@ -179,7 +179,7 @@ _CanvasItemId: TypeAlias = int
 _Color: TypeAlias = str  # typically '#rrggbb', '#rgb' or color names.
 _Compound: TypeAlias = Literal["top", "left", "center", "right", "bottom", "none"]  # -compound in manual page named 'options'
 # manual page: Tk_GetCursor
-_Cursor: TypeAlias = Union[str, tuple[str], tuple[str, str], tuple[str, str, str], tuple[str, str, str, str]]
+_Cursor: TypeAlias = str | tuple[str] | tuple[str, str] | tuple[str, str, str] | tuple[str, str, str, str]
 # example when it's sequence:  entry['invalidcommand'] = [entry.register(print), '%P']
 _EntryValidateCommand: TypeAlias = str | list[str] | tuple[str, ...] | Callable[[], bool]
 _GridIndex: TypeAlias = int | str
@@ -188,7 +188,7 @@ _Relief: TypeAlias = Literal["raised", "sunken", "flat", "ridge", "solid", "groo
 _ScreenUnits: TypeAlias = str | float  # Often the right type instead of int. Manual page: Tk_GetPixels
 # -xscrollcommand and -yscrollcommand in 'options' manual page
 _XYScrollCommand: TypeAlias = str | Callable[[float, float], object]
-_TakeFocusValue: TypeAlias = Union[int, Literal[""], Callable[[str], bool | None]]  # -takefocus in manual page named 'options'
+_TakeFocusValue: TypeAlias = int | Literal[""] | Callable[[str], bool | None]  # -takefocus in manual page named 'options'
 
 if sys.version_info >= (3, 11):
     class _VersionInfoType(NamedTuple):
diff --git a/stdlib/tkinter/ttk.pyi b/stdlib/tkinter/ttk.pyi
index bd477535f41f..61ebc0e2734f 100644
--- a/stdlib/tkinter/ttk.pyi
+++ b/stdlib/tkinter/ttk.pyi
@@ -4,7 +4,7 @@ import tkinter
 from _typeshed import Incomplete
 from collections.abc import Callable
 from tkinter.font import _FontDescription
-from typing import Any, Union, overload
+from typing import Any, overload
 from typing_extensions import Literal, TypeAlias, TypedDict
 
 __all__ = [
@@ -38,13 +38,13 @@ __all__ = [
 def tclobjs_to_py(adict: dict[Any, Any]) -> dict[Any, Any]: ...
 def setup_master(master: Incomplete | None = None): ...
 
-_Padding: TypeAlias = Union[
-    tkinter._ScreenUnits,
-    tuple[tkinter._ScreenUnits],
-    tuple[tkinter._ScreenUnits, tkinter._ScreenUnits],
-    tuple[tkinter._ScreenUnits, tkinter._ScreenUnits, tkinter._ScreenUnits],
-    tuple[tkinter._ScreenUnits, tkinter._ScreenUnits, tkinter._ScreenUnits, tkinter._ScreenUnits],
-]
+_Padding: TypeAlias = (
+    tkinter._ScreenUnits
+    | tuple[tkinter._ScreenUnits]
+    | tuple[tkinter._ScreenUnits, tkinter._ScreenUnits]
+    | tuple[tkinter._ScreenUnits, tkinter._ScreenUnits, tkinter._ScreenUnits]
+    | tuple[tkinter._ScreenUnits, tkinter._ScreenUnits, tkinter._ScreenUnits, tkinter._ScreenUnits]
+)
 
 # from ttk_widget (aka ttk::widget) manual page, differs from tkinter._Compound
 _TtkCompound: TypeAlias = Literal["text", "image", tkinter._Compound]
diff --git a/stdlib/tracemalloc.pyi b/stdlib/tracemalloc.pyi
index d7214de285f8..3dc8b8603fe5 100644
--- a/stdlib/tracemalloc.pyi
+++ b/stdlib/tracemalloc.pyi
@@ -1,7 +1,7 @@
 import sys
 from _tracemalloc import *
 from collections.abc import Sequence
-from typing import Any, Union, overload
+from typing import Any, overload
 from typing_extensions import SupportsIndex, TypeAlias
 
 def get_object_traceback(obj: object) -> Traceback | None: ...
@@ -67,7 +67,7 @@ class Frame:
         def __le__(self, other: Frame, NotImplemented: Any = ...) -> bool: ...
 
 if sys.version_info >= (3, 9):
-    _TraceTuple: TypeAlias = Union[tuple[int, int, Sequence[_FrameTuple], int | None], tuple[int, int, Sequence[_FrameTuple]]]
+    _TraceTuple: TypeAlias = tuple[int, int, Sequence[_FrameTuple], int | None] | tuple[int, int, Sequence[_FrameTuple]]
 else:
     _TraceTuple: TypeAlias = tuple[int, int, Sequence[_FrameTuple]]
 
diff --git a/stdlib/turtle.pyi b/stdlib/turtle.pyi
index 1259ca6fb4cc..2187d13b1a13 100644
--- a/stdlib/turtle.pyi
+++ b/stdlib/turtle.pyi
@@ -1,7 +1,7 @@
 from _typeshed import Self
 from collections.abc import Callable, Sequence
 from tkinter import Canvas, Frame, Misc, PhotoImage, Scrollbar
-from typing import Any, ClassVar, Union, overload
+from typing import Any, ClassVar, overload
 from typing_extensions import TypeAlias
 
 __all__ = [
@@ -133,7 +133,7 @@ __all__ = [
 # alias we use for return types. Really, these two aliases should be the
 # same, but as per the "no union returns" typeshed policy, we'll return
 # Any instead.
-_Color: TypeAlias = Union[str, tuple[float, float, float]]
+_Color: TypeAlias = str | tuple[float, float, float]
 _AnyColor: TypeAlias = Any
 
 # TODO: Replace this with a TypedDict once it becomes standardized.
diff --git a/stdlib/unittest/case.pyi b/stdlib/unittest/case.pyi
index 5b1bd9288659..630267a7ce07 100644
--- a/stdlib/unittest/case.pyi
+++ b/stdlib/unittest/case.pyi
@@ -6,20 +6,7 @@ from collections.abc import Callable, Container, Iterable, Mapping, Sequence, Se
 from contextlib import AbstractContextManager
 from re import Pattern
 from types import TracebackType
-from typing import (
-    Any,
-    AnyStr,
-    ClassVar,
-    Generic,
-    NamedTuple,
-    NoReturn,
-    Protocol,
-    SupportsAbs,
-    SupportsRound,
-    TypeVar,
-    Union,
-    overload,
-)
+from typing import Any, AnyStr, ClassVar, Generic, NamedTuple, NoReturn, Protocol, SupportsAbs, SupportsRound, TypeVar, overload
 from typing_extensions import ParamSpec, TypeAlias
 from warnings import WarningMessage
 
@@ -82,9 +69,9 @@ class SkipTest(Exception):
 class _SupportsAbsAndDunderGE(SupportsDunderGE[Any], SupportsAbs[Any], Protocol): ...
 
 if sys.version_info >= (3, 10):
-    _IsInstanceClassInfo: TypeAlias = Union[type, UnionType, tuple[type | UnionType | tuple[Any, ...], ...]]
+    _IsInstanceClassInfo: TypeAlias = type | UnionType | tuple[type | UnionType | tuple[Any, ...], ...]
 else:
-    _IsInstanceClassInfo: TypeAlias = Union[type, tuple[type | tuple[Any, ...], ...]]
+    _IsInstanceClassInfo: TypeAlias = type | tuple[type | tuple[Any, ...], ...]
 
 class TestCase:
     failureException: type[BaseException]
diff --git a/stdlib/xmlrpc/client.pyi b/stdlib/xmlrpc/client.pyi
index 536cd6382d0b..86d21abd7725 100644
--- a/stdlib/xmlrpc/client.pyi
+++ b/stdlib/xmlrpc/client.pyi
@@ -7,7 +7,7 @@ from collections.abc import Callable, Iterable, Mapping
 from datetime import datetime
 from io import BytesIO
 from types import TracebackType
-from typing import Any, Protocol, Union, overload
+from typing import Any, Protocol, overload
 from typing_extensions import Literal, TypeAlias
 
 class _SupportsTimeTuple(Protocol):
@@ -31,7 +31,7 @@ _Marshallable: TypeAlias = (
     | Binary
 )
 _XMLDate: TypeAlias = int | datetime | tuple[int, ...] | time.struct_time
-_HostType: TypeAlias = Union[tuple[str, dict[str, str]], str]
+_HostType: TypeAlias = tuple[str, dict[str, str]] | str
 
 def escape(s: str) -> str: ...  # undocumented
 
diff --git a/stubs/Pillow/PIL/Image.pyi b/stubs/Pillow/PIL/Image.pyi
index c5655f0e37be..c2be2dcd23cd 100644
--- a/stubs/Pillow/PIL/Image.pyi
+++ b/stubs/Pillow/PIL/Image.pyi
@@ -2,7 +2,7 @@ from _typeshed import Incomplete, Self, SupportsRead, SupportsWrite
 from collections.abc import Callable, Iterable, Iterator, MutableMapping, Sequence
 from enum import IntEnum
 from pathlib import Path
-from typing import Any, ClassVar, Protocol, SupportsBytes, Union
+from typing import Any, ClassVar, Protocol, SupportsBytes
 from typing_extensions import Literal, TypeAlias
 
 from PIL.PyAccess import PyAccess
@@ -22,13 +22,13 @@ _Resample: TypeAlias = Literal[0, 1, 2, 3, 4, 5]
 _Size: TypeAlias = tuple[int, int]
 _Box: TypeAlias = tuple[int, int, int, int]
 
-_ConversionMatrix: TypeAlias = Union[
-    tuple[float, float, float, float], tuple[float, float, float, float, float, float, float, float, float, float, float, float]
-]
+_ConversionMatrix: TypeAlias = (
+    tuple[float, float, float, float] | tuple[float, float, float, float, float, float, float, float, float, float, float, float]
+)
 # `str` values are only accepted if mode="RGB" for an `Image` object
 # `float` values are only accepted for certain modes such as "F"
 # See https://pillow.readthedocs.io/en/stable/reference/Image.html#PIL.Image.new
-_Color: TypeAlias = Union[int, tuple[int], tuple[int, int, int], tuple[int, int, int, int], str, float, tuple[float]]
+_Color: TypeAlias = int | tuple[int] | tuple[int, int, int] | tuple[int, int, int, int] | str | float | tuple[float]
 
 class _Writeable(SupportsWrite[bytes], Protocol):
     def seek(self, __offset: int) -> Any: ...
diff --git a/stubs/Pillow/PIL/ImageColor.pyi b/stubs/Pillow/PIL/ImageColor.pyi
index 1815d7004f50..62fba216bb57 100644
--- a/stubs/Pillow/PIL/ImageColor.pyi
+++ b/stubs/Pillow/PIL/ImageColor.pyi
@@ -1,7 +1,6 @@
-from typing import Union
 from typing_extensions import TypeAlias
 
-_RGB: TypeAlias = Union[tuple[int, int, int], tuple[int, int, int, int]]
+_RGB: TypeAlias = tuple[int, int, int] | tuple[int, int, int, int]
 _Ink: TypeAlias = str | int | _RGB
 _GreyScale: TypeAlias = tuple[int, int]
 
diff --git a/stubs/Pillow/PIL/ImageOps.pyi b/stubs/Pillow/PIL/ImageOps.pyi
index aa082e5f8b9f..9cc148018e8f 100644
--- a/stubs/Pillow/PIL/ImageOps.pyi
+++ b/stubs/Pillow/PIL/ImageOps.pyi
@@ -1,12 +1,12 @@
 from _typeshed import Incomplete
 from collections.abc import Iterable
-from typing import Protocol, Union
+from typing import Protocol
 from typing_extensions import TypeAlias
 
 from .Image import Image, Resampling, _Resample, _Size
 from .ImageColor import _Ink
 
-_Border: TypeAlias = Union[int, tuple[int, int], tuple[int, int, int, int]]
+_Border: TypeAlias = int | tuple[int, int] | tuple[int, int, int, int]
 
 class _Deformer(Protocol):
     def getmesh(self, image: Image): ...
diff --git a/stubs/Pillow/PIL/TiffTags.pyi b/stubs/Pillow/PIL/TiffTags.pyi
index 4bef226ae4ef..f546f604b81b 100644
--- a/stubs/Pillow/PIL/TiffTags.pyi
+++ b/stubs/Pillow/PIL/TiffTags.pyi
@@ -1,5 +1,5 @@
 from _typeshed import Incomplete
-from typing import Any, NamedTuple, Union
+from typing import Any, NamedTuple
 from typing_extensions import Literal, TypeAlias
 
 class _TagInfo(NamedTuple):
@@ -37,7 +37,7 @@ DOUBLE: Literal[12]
 IFD: Literal[13]
 
 _TagType: TypeAlias = Literal[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]
-_TagTuple: TypeAlias = Union[tuple[str, _TagType, int], tuple[str, _TagInfo, int, dict[str, int]]]
+_TagTuple: TypeAlias = tuple[str, _TagType, int] | tuple[str, _TagInfo, int, dict[str, int]]
 
 TAGS_V2: dict[int, _TagTuple]
 TAGS_V2_GROUPS: dict[int, dict[int, _TagTuple]]
diff --git a/stubs/jsonschema/jsonschema/_format.pyi b/stubs/jsonschema/jsonschema/_format.pyi
index 2f3df1bd77e8..9c2b12ef186e 100644
--- a/stubs/jsonschema/jsonschema/_format.pyi
+++ b/stubs/jsonschema/jsonschema/_format.pyi
@@ -1,10 +1,10 @@
 from collections.abc import Callable, Iterable
-from typing import TypeVar, Union
+from typing import TypeVar
 from typing_extensions import TypeAlias
 
 _FormatCheckCallable: TypeAlias = Callable[[object], bool]
 _F = TypeVar("_F", bound=_FormatCheckCallable)
-_RaisesType: TypeAlias = Union[type[Exception], tuple[type[Exception], ...]]
+_RaisesType: TypeAlias = type[Exception] | tuple[type[Exception], ...]
 
 class FormatChecker:
     checkers: dict[str, tuple[_FormatCheckCallable, _RaisesType]]
diff --git a/stubs/keyboard/keyboard/__init__.pyi b/stubs/keyboard/keyboard/__init__.pyi
index bfc19bc051c4..d65c0c508f33 100644
--- a/stubs/keyboard/keyboard/__init__.pyi
+++ b/stubs/keyboard/keyboard/__init__.pyi
@@ -1,7 +1,6 @@
 from collections.abc import Callable, Generator, Iterable, Sequence
 from queue import Queue
 from threading import Event as _UninterruptibleEvent
-from typing import Optional
 from typing_extensions import TypeAlias
 
 from ._canonical_names import all_modifiers as all_modifiers, sided_modifiers as sided_modifiers
@@ -10,7 +9,7 @@ from ._keyboard_event import KEY_DOWN as KEY_DOWN, KEY_UP as KEY_UP, KeyboardEve
 _Key: TypeAlias = int | str
 _ScanCodeList: TypeAlias = list[int] | tuple[int, ...]
 _ParseableHotkey: TypeAlias = _Key | list[int | _ScanCodeList] | tuple[int | _ScanCodeList, ...]
-_Callback: TypeAlias = Callable[[KeyboardEvent], Optional[bool]] | Callable[[], Optional[bool]]
+_Callback: TypeAlias = Callable[[KeyboardEvent], bool | None] | Callable[[], bool | None]
 # mypy doesn't support PEP 646's TypeVarTuple yet: https://github.com/python/mypy/issues/12280
 # _Ts = TypeVarTuple("_Ts")
 _Ts: TypeAlias = tuple[object, ...]
diff --git a/stubs/netaddr/netaddr/ip/__init__.pyi b/stubs/netaddr/netaddr/ip/__init__.pyi
index 7125323f190e..c05525246d8a 100644
--- a/stubs/netaddr/netaddr/ip/__init__.pyi
+++ b/stubs/netaddr/netaddr/ip/__init__.pyi
@@ -1,7 +1,7 @@
 from _typeshed import Incomplete, Self
 from abc import abstractmethod
 from collections.abc import Iterable, Iterator
-from typing import SupportsInt, Union, overload
+from typing import SupportsInt, overload
 from typing_extensions import Literal, SupportsIndex, TypeAlias
 
 from netaddr.core import DictDotLookup
@@ -38,7 +38,7 @@ class BaseIP:
     def version(self) -> Literal[4, 6]: ...
 
 _IPAddressAddr: TypeAlias = BaseIP | int | str
-_IPNetworkAddr: TypeAlias = Union[IPNetwork, IPAddress, tuple[int, int], str]
+_IPNetworkAddr: TypeAlias = IPNetwork | IPAddress | tuple[int, int] | str
 
 class IPAddress(BaseIP):
     def __init__(self, addr: _IPAddressAddr, version: Literal[4, 6] | None = ..., flags: int = ...) -> None: ...
diff --git a/stubs/paho-mqtt/paho/mqtt/client.pyi b/stubs/paho-mqtt/paho/mqtt/client.pyi
index 3a3b0f1e4bc5..a06eddcca262 100644
--- a/stubs/paho-mqtt/paho/mqtt/client.pyi
+++ b/stubs/paho-mqtt/paho/mqtt/client.pyi
@@ -5,7 +5,7 @@ import time
 import types
 from _typeshed import Incomplete
 from collections.abc import Callable
-from typing import Any, Optional, TypeVar
+from typing import Any, TypeVar
 from typing_extensions import TypeAlias
 
 from .matcher import MQTTMatcher as MQTTMatcher
@@ -92,7 +92,7 @@ _Payload: TypeAlias = str | bytes | bytearray | float
 _ExtraHeader: TypeAlias = dict[str, str] | Callable[[dict[str, str]], dict[str, str]]
 _OnLog: TypeAlias = Callable[[Client, _UserData, int, str], object]
 _OnConnect: TypeAlias = Callable[[Client, _UserData, dict[str, int], int], object]
-_OnConnectV5: TypeAlias = Callable[[Client, _UserData, dict[str, int], ReasonCodes, Optional[Properties]], object]
+_OnConnectV5: TypeAlias = Callable[[Client, _UserData, dict[str, int], ReasonCodes, Properties | None], object]
 _TOnConnect = TypeVar("_TOnConnect", _OnConnect, _OnConnectV5)
 _OnConnectFail: TypeAlias = Callable[[Client, _UserData], object]
 _OnSubscribe: TypeAlias = Callable[[Client, _UserData, int, tuple[int]], object]
@@ -104,7 +104,7 @@ _OnUnsubscribe: TypeAlias = Callable[[Client, _UserData, int], object]
 _OnUnsubscribeV5: TypeAlias = Callable[[Client, _UserData, int, Properties, list[ReasonCodes] | ReasonCodes], object]
 _TOnUnsubscribe = TypeVar("_TOnUnsubscribe", _OnUnsubscribe, _OnUnsubscribeV5)
 _OnDisconnect: TypeAlias = Callable[[Client, _UserData, int], object]
-_OnDisconnectV5: TypeAlias = Callable[[Client, _UserData, Optional[ReasonCodes], Optional[Properties]], object]
+_OnDisconnectV5: TypeAlias = Callable[[Client, _UserData, ReasonCodes | None, Properties | None], object]
 _TOnDisconnect = TypeVar("_TOnDisconnect", _OnDisconnect, _OnDisconnectV5)
 _OnSocket: TypeAlias = Callable[[Client, _UserData, _Socket | WebsocketWrapper | None], object]
 
diff --git a/stubs/parsimonious/parsimonious/expressions.pyi b/stubs/parsimonious/parsimonious/expressions.pyi
index fdc50b071c7d..482390b14f63 100644
--- a/stubs/parsimonious/parsimonious/expressions.pyi
+++ b/stubs/parsimonious/parsimonious/expressions.pyi
@@ -2,7 +2,7 @@ import collections.abc
 from _typeshed import Self
 from collections.abc import Callable, Mapping
 from re import Pattern
-from typing import Any, Union
+from typing import Any
 from typing_extensions import TypeAlias
 
 from parsimonious.exceptions import ParseError
@@ -10,7 +10,7 @@ from parsimonious.grammar import Grammar
 from parsimonious.nodes import Node
 from parsimonious.utils import StrAndRepr
 
-_CALLABLE_RETURN_TYPE: TypeAlias = Union[int, tuple[int, list[Node]], Node, None]
+_CALLABLE_RETURN_TYPE: TypeAlias = int | tuple[int, list[Node]] | Node | None
 _CALLABLE_TYPE: TypeAlias = (
     Callable[[str, int], _CALLABLE_RETURN_TYPE]
     | Callable[[str, int, Mapping[tuple[int, int], Node], ParseError, Grammar], _CALLABLE_RETURN_TYPE]
diff --git a/stubs/python-xlib/Xlib/_typing.pyi b/stubs/python-xlib/Xlib/_typing.pyi
index 34d5b3cd4620..f7dd1ca6ced0 100644
--- a/stubs/python-xlib/Xlib/_typing.pyi
+++ b/stubs/python-xlib/Xlib/_typing.pyi
@@ -1,12 +1,12 @@
 from _typeshed import FileDescriptor, StrOrBytesPath
 from collections.abc import Callable
-from typing import Optional, TypeVar
+from typing import TypeVar
 from typing_extensions import TypeAlias
 
 from Xlib.error import XError
 from Xlib.protocol.rq import Request
 
 _T = TypeVar("_T")
-ErrorHandler: TypeAlias = Callable[[XError, Optional[Request]], _T]
+ErrorHandler: TypeAlias = Callable[[XError, Request | None], _T]
 Unused: TypeAlias = object
 OpenFile: TypeAlias = StrOrBytesPath | FileDescriptor
diff --git a/stubs/python-xlib/Xlib/ext/composite.pyi b/stubs/python-xlib/Xlib/ext/composite.pyi
index 96123fcf6ec9..f974c1365b7d 100644
--- a/stubs/python-xlib/Xlib/ext/composite.pyi
+++ b/stubs/python-xlib/Xlib/ext/composite.pyi
@@ -1,5 +1,5 @@
 from collections.abc import Callable
-from typing import Any, Union
+from typing import Any
 from typing_extensions import TypeAlias
 
 from Xlib._typing import ErrorHandler, Unused
@@ -7,7 +7,7 @@ from Xlib.display import Display
 from Xlib.protocol import rq
 from Xlib.xobject import drawable, resource
 
-_Update: TypeAlias = Callable[[Union[rq.DictWrapper, dict[str, Any]]], object]
+_Update: TypeAlias = Callable[[rq.DictWrapper | dict[str, Any]], object]
 
 extname: str
 RedirectAutomatic: int
diff --git a/stubs/requests/requests/sessions.pyi b/stubs/requests/requests/sessions.pyi
index d0da69ead3b0..95cb7381e986 100644
--- a/stubs/requests/requests/sessions.pyi
+++ b/stubs/requests/requests/sessions.pyi
@@ -1,6 +1,6 @@
 from _typeshed import Incomplete, Self, SupportsItems, SupportsRead
 from collections.abc import Callable, Iterable, Mapping, MutableMapping
-from typing import Any, Union
+from typing import Any
 from typing_extensions import TypeAlias, TypedDict
 
 from urllib3._collections import RecentlyUsedContainer
@@ -77,8 +77,8 @@ _Data: TypeAlias = (
     | tuple[tuple[Any, Any], ...]
     | Mapping[Any, Any]
 )
-_Auth: TypeAlias = Union[tuple[str, str], _auth.AuthBase, Callable[[PreparedRequest], PreparedRequest]]
-_Cert: TypeAlias = Union[str, tuple[str, str]]
+_Auth: TypeAlias = tuple[str, str] | _auth.AuthBase | Callable[[PreparedRequest], PreparedRequest]
+_Cert: TypeAlias = str | tuple[str, str]
 # Files is passed to requests.utils.to_key_val_list()
 _FileName: TypeAlias = str | None
 _FileContent: TypeAlias = SupportsRead[str | bytes] | str | bytes
@@ -94,15 +94,16 @@ _HooksInput: TypeAlias = Mapping[str, Iterable[_Hook] | _Hook]
 
 _ParamsMappingKeyType: TypeAlias = str | bytes | int | float
 _ParamsMappingValueType: TypeAlias = str | bytes | int | float | Iterable[str | bytes | int | float] | None
-_Params: TypeAlias = Union[
-    SupportsItems[_ParamsMappingKeyType, _ParamsMappingValueType],
-    tuple[_ParamsMappingKeyType, _ParamsMappingValueType],
-    Iterable[tuple[_ParamsMappingKeyType, _ParamsMappingValueType]],
-    str | bytes,
-]
+_Params: TypeAlias = (
+    SupportsItems[_ParamsMappingKeyType, _ParamsMappingValueType]
+    | tuple[_ParamsMappingKeyType, _ParamsMappingValueType]
+    | Iterable[tuple[_ParamsMappingKeyType, _ParamsMappingValueType]]
+    | str
+    | bytes
+)
 _TextMapping: TypeAlias = MutableMapping[str, str]
 _HeadersUpdateMapping: TypeAlias = Mapping[str, str | bytes | None]
-_Timeout: TypeAlias = Union[float, tuple[float, float], tuple[float, None]]
+_Timeout: TypeAlias = float | tuple[float, float] | tuple[float, None]
 _Verify: TypeAlias = bool | str
 
 class _Settings(TypedDict):
diff --git a/stubs/setuptools/setuptools/_distutils/ccompiler.pyi b/stubs/setuptools/setuptools/_distutils/ccompiler.pyi
index 5b92c5f5c42e..96a756bb2cf8 100644
--- a/stubs/setuptools/setuptools/_distutils/ccompiler.pyi
+++ b/stubs/setuptools/setuptools/_distutils/ccompiler.pyi
@@ -1,8 +1,8 @@
 from collections.abc import Callable
-from typing import Any, Union
+from typing import Any
 from typing_extensions import TypeAlias
 
-_Macro: TypeAlias = Union[tuple[str], tuple[str, str | None]]
+_Macro: TypeAlias = tuple[str] | tuple[str, str | None]
 
 def gen_lib_options(
     compiler: CCompiler, library_dirs: list[str], runtime_library_dirs: list[str], libraries: list[str]
diff --git a/stubs/urllib3/urllib3/fields.pyi b/stubs/urllib3/urllib3/fields.pyi
index 8127d72d6968..a7eb02554374 100644
--- a/stubs/urllib3/urllib3/fields.pyi
+++ b/stubs/urllib3/urllib3/fields.pyi
@@ -1,9 +1,9 @@
 from collections.abc import Callable, Mapping
-from typing import Any, Union
+from typing import Any
 from typing_extensions import TypeAlias
 
 _FieldValue: TypeAlias = str | bytes
-_FieldValueTuple: TypeAlias = Union[_FieldValue, tuple[str, _FieldValue], tuple[str, _FieldValue, str]]
+_FieldValueTuple: TypeAlias = _FieldValue | tuple[str, _FieldValue] | tuple[str, _FieldValue, str]
 
 def guess_content_type(filename: str | None, default: str = ...) -> str: ...
 def format_header_param_rfc2231(name: str, value: _FieldValue) -> str: ...
diff --git a/tests/check_new_syntax.py b/tests/check_new_syntax.py
index 4c47557caceb..c99c0137be06 100755
--- a/tests/check_new_syntax.py
+++ b/tests/check_new_syntax.py
@@ -10,68 +10,6 @@
 
 def check_new_syntax(tree: ast.AST, path: Path, stub: str) -> list[str]:
     errors = []
-    sourcelines = stub.splitlines()
-
-    class AnnotationUnionFinder(ast.NodeVisitor):
-        def visit_Subscript(self, node: ast.Subscript) -> None:
-            if isinstance(node.value, ast.Name):
-                if node.value.id == "Union" and isinstance(node.slice, ast.Tuple):
-                    new_syntax = " | ".join(ast.unparse(x) for x in node.slice.elts)
-                    errors.append(f"{path}:{node.lineno}: Use PEP 604 syntax for Union, e.g. `{new_syntax}`")
-                if node.value.id == "Optional":
-                    new_syntax = f"{ast.unparse(node.slice)} | None"
-                    errors.append(f"{path}:{node.lineno}: Use PEP 604 syntax for Optional, e.g. `{new_syntax}`")
-
-            self.generic_visit(node)
-
-    class NonAnnotationUnionFinder(ast.NodeVisitor):
-        def visit_Subscript(self, node: ast.Subscript) -> None:
-            if isinstance(node.value, ast.Name):
-                nodelines = sourcelines[(node.lineno - 1) : node.end_lineno]
-                for line in nodelines:
-                    # A hack to workaround various PEP 604 bugs in mypy
-                    if any(x in line for x in {"tuple[", "Callable[", "type["}):
-                        return None
-                if node.value.id == "Union" and isinstance(node.slice, ast.Tuple):
-                    new_syntax = " | ".join(ast.unparse(x) for x in node.slice.elts)
-                    errors.append(f"{path}:{node.lineno}: Use PEP 604 syntax for Union, e.g. `{new_syntax}`")
-                elif node.value.id == "Optional":
-                    new_syntax = f"{ast.unparse(node.slice)} | None"
-                    errors.append(f"{path}:{node.lineno}: Use PEP 604 syntax for Optional, e.g. `{new_syntax}`")
-
-            self.generic_visit(node)
-
-    class OldSyntaxFinder(ast.NodeVisitor):
-        def visit_AnnAssign(self, node: ast.AnnAssign) -> None:
-            AnnotationUnionFinder().visit(node.annotation)
-            if node.value is not None:
-                NonAnnotationUnionFinder().visit(node.value)
-            self.generic_visit(node)
-
-        def visit_arg(self, node: ast.arg) -> None:
-            if node.annotation is not None:
-                AnnotationUnionFinder().visit(node.annotation)
-            self.generic_visit(node)
-
-        def _visit_function(self, node: ast.FunctionDef | ast.AsyncFunctionDef) -> None:
-            if node.returns is not None:
-                AnnotationUnionFinder().visit(node.returns)
-            self.generic_visit(node)
-
-        def visit_FunctionDef(self, node: ast.FunctionDef) -> None:
-            self._visit_function(node)
-
-        def visit_AsyncFunctionDef(self, node: ast.AsyncFunctionDef) -> None:
-            self._visit_function(node)
-
-        def visit_Assign(self, node: ast.Assign) -> None:
-            NonAnnotationUnionFinder().visit(node.value)
-            self.generic_visit(node)
-
-        def visit_ClassDef(self, node: ast.ClassDef) -> None:
-            for base in node.bases:
-                NonAnnotationUnionFinder().visit(base)
-            self.generic_visit(node)
 
     class IfFinder(ast.NodeVisitor):
         def visit_If(self, node: ast.If) -> None:
@@ -88,7 +26,6 @@ def visit_If(self, node: ast.If) -> None:
                 )
             self.generic_visit(node)
 
-    OldSyntaxFinder().visit(tree)
     IfFinder().visit(tree)
     return errors