diff --git a/pydantic_ai/_pydantic.py b/pydantic_ai/_pydantic.py
index 9fabcd84d..58c98f5ab 100644
--- a/pydantic_ai/_pydantic.py
+++ b/pydantic_ai/_pydantic.py
@@ -6,7 +6,7 @@
 from __future__ import annotations as _annotations
 
 from inspect import Parameter, Signature, signature
-from typing import Any, Callable, Literal, TypedDict, Union, cast, get_origin
+from typing import Any, Callable, Literal, TypedDict, cast, get_origin
 
 from _griffe.enumerations import DocstringSectionKind
 from _griffe.models import Docstring, Object as GriffeObject
@@ -31,9 +31,9 @@ class FunctionSchema(TypedDict):
     json_schema: ObjectJsonSchema
     takes_info: bool
     # if not None, the function takes a single by that name (besides potentially `info`)
-    single_arg_name: Union[str, None]
+    single_arg_name: str | None
     positional_fields: list[str]
-    var_positional_field: Union[str, None]
+    var_positional_field: str | None
 
 
 def function_schema(function: Callable[..., Any]) -> FunctionSchema:
@@ -55,10 +55,10 @@ def function_schema(function: Callable[..., Any]) -> FunctionSchema:
 
     type_hints = _typing_extra.get_function_type_hints(function)
 
-    var_kwargs_schema: Union[core_schema.CoreSchema, None] = None
+    var_kwargs_schema: core_schema.CoreSchema | None = None
     fields: dict[str, core_schema.TypedDictField] = {}
     positional_fields: list[str] = []
-    var_positional_field: Union[str, None] = None
+    var_positional_field: str | None = None
     errors: list[str] = []
     decorators = _decorators.DecoratorInfos()
     description, field_descriptions = _doc_descriptions(function, sig)
@@ -129,10 +129,10 @@ def function_schema(function: Callable[..., Any]) -> FunctionSchema:
 
 def _build_schema(
     fields: dict[str, core_schema.TypedDictField],
-    var_kwargs_schema: Union[core_schema.CoreSchema, None],
+    var_kwargs_schema: core_schema.CoreSchema | None,
     gen_schema: _generate_schema.GenerateSchema,
     core_config: core_schema.CoreConfig,
-) -> tuple[core_schema.CoreSchema, Union[str, None]]:
+) -> tuple[core_schema.CoreSchema, str | None]:
     """Generate a typed dict schema for function parameters.
 
     Args:
@@ -163,7 +163,7 @@ def _build_schema(
 
 
 def _doc_descriptions(
-    func: Callable[..., Any], sig: Signature, *, style: Union[DocstringStyle, None] = None
+    func: Callable[..., Any], sig: Signature, *, style: DocstringStyle | None = None
 ) -> tuple[str, dict[str, str]]:
     """Extract the function description and parameter descriptions from a function's docstring.
 
diff --git a/pydantic_ai/_utils.py b/pydantic_ai/_utils.py
index c86bd8b01..5521a6e40 100644
--- a/pydantic_ai/_utils.py
+++ b/pydantic_ai/_utils.py
@@ -1,3 +1,5 @@
+from __future__ import annotations as _annotations
+
 import asyncio
 from dataclasses import dataclass, is_dataclass
 from functools import partial
@@ -102,14 +104,14 @@ def __init__(self, *, left: _Left) -> None: ...
     @overload
     def __init__(self, *, right: _Right) -> None: ...
 
-    def __init__(self, *, left: Union[_Left, None] = None, right: Union[_Right, None] = None) -> None:
+    def __init__(self, *, left: _Left | None = None, right: _Right | None = None) -> None:
         if (left is not None and right is not None) or (left is None and right is None):
             raise TypeError('Either must have exactly one value')
         self._left = left
         self._right = right
 
     @property
-    def left(self) -> Union[_Left, None]:
+    def left(self) -> _Left | None:
         return self._left
 
     @property
diff --git a/pydantic_ai/agent.py b/pydantic_ai/agent.py
index 021969004..15b1c32e8 100644
--- a/pydantic_ai/agent.py
+++ b/pydantic_ai/agent.py
@@ -22,16 +22,16 @@ class Agent(Generic[ResultData, AgentContext]):
 
     def __init__(
         self,
-        model: Union[_models.Model, KnownModelName, None] = None,
+        model: _models.Model | KnownModelName | None = None,
         response_type: type[_result.ResultData] = str,
         *,
-        system_prompt: Union[str, Sequence[str]] = (),
+        system_prompt: str | Sequence[str] = (),
         retrievers: Sequence[_r.Retriever[AgentContext, Any]] = (),
         context: AgentContext = None,
         retries: int = 1,
         response_schema_name: str = 'final_response',
         response_schema_description: str = 'The final response',
-        response_retries: Union[int, None] = None,
+        response_retries: int | None = None,
     ):
         self._model = _models.infer_model(model) if model is not None else None
 
@@ -55,8 +55,8 @@ async def run(
         self,
         user_prompt: str,
         *,
-        message_history: Union[list[_messages.Message], None] = None,
-        model: Union[_models.Model, KnownModelName, None] = None,
+        message_history: list[_messages.Message] | None = None,
+        model: _models.Model | KnownModelName | None = None,
     ) -> _result.RunResult[_result.ResultData]:
         """Run the agent with a user prompt in async mode.
 
@@ -101,8 +101,8 @@ def run_sync(
         self,
         user_prompt: str,
         *,
-        message_history: Union[list[_messages.Message], None] = None,
-        model: Union[_models.Model, KnownModelName, None] = None,
+        message_history: list[_messages.Message] | None = None,
+        model: _models.Model | KnownModelName | None = None,
     ) -> _result.RunResult[_result.ResultData]:
         """Run the agent with a user prompt synchronously.
 
@@ -132,14 +132,14 @@ def retriever(self, func: _r.RetrieverFunc[AgentContext, _r.P], /) -> _r.Retriev
 
     @overload
     def retriever(
-        self, /, *, retries: Union[int, None] = None
+        self, /, *, retries: int | None = None
     ) -> Callable[
         [_r.RetrieverFunc[AgentContext, _r.P]],
         _r.Retriever[AgentContext, _r.P],
     ]: ...
 
     def retriever(
-        self, func: Union[_r.RetrieverFunc[AgentContext, _r.P], None] = None, /, *, retries: Union[int, None] = None
+        self, func: _r.RetrieverFunc[AgentContext, _r.P] | None = None, /, *, retries: int | None = None
     ) -> Any:
         """Decorator to register a retriever function."""
         if func is None:
@@ -153,7 +153,7 @@ def retriever_decorator(func_: _r.RetrieverFunc[AgentContext, _r.P]) -> _r.Retri
             return self._register_retriever(func, retries)
 
     def _register_retriever(
-        self, func: _r.RetrieverFunc[AgentContext, _r.P], retries: Union[int, None]
+        self, func: _r.RetrieverFunc[AgentContext, _r.P], retries: int | None
     ) -> _r.Retriever[AgentContext, _r.P]:
         retries_ = retries if retries is not None else self._default_retries
         retriever = _r.Retriever[AgentContext, _r.P].build(func, retries_)
diff --git a/pydantic_ai/messages.py b/pydantic_ai/messages.py
index 11eaf2088..4c69244fb 100644
--- a/pydantic_ai/messages.py
+++ b/pydantic_ai/messages.py
@@ -1,3 +1,5 @@
+from __future__ import annotations as _annotations
+
 import json
 from dataclasses import dataclass, field
 from datetime import datetime
@@ -37,7 +39,7 @@ def llm_response(self) -> str:
 class FunctionRetry:
     function_id: str
     function_name: str
-    content: Union[list[pydantic_core.ErrorDetails], str]
+    content: list[pydantic_core.ErrorDetails] | str
     timestamp: datetime = field(default_factory=datetime.now)
     role: Literal['function-retry'] = 'function-retry'
 
diff --git a/pydantic_ai/models/__init__.py b/pydantic_ai/models/__init__.py
index aab7320e2..c3118b898 100644
--- a/pydantic_ai/models/__init__.py
+++ b/pydantic_ai/models/__init__.py
@@ -6,7 +6,7 @@
 from __future__ import annotations as _annotations
 
 from abc import ABC, abstractmethod
-from typing import TYPE_CHECKING, Protocol, Union
+from typing import TYPE_CHECKING, Protocol
 
 from ..messages import LLMMessage, Message
 
@@ -35,7 +35,7 @@ async def request(self, messages: list[Message]) -> LLMMessage:
     # TODO streamed response
 
 
-def infer_model(model: Union[Model, KnownModelName]) -> Model:
+def infer_model(model: Model | KnownModelName) -> Model:
     """Infer the model from the name."""
     if isinstance(model, Model):
         return model
diff --git a/pydantic_ai/models/openai.py b/pydantic_ai/models/openai.py
index 6c572cfad..addc2785c 100644
--- a/pydantic_ai/models/openai.py
+++ b/pydantic_ai/models/openai.py
@@ -1,7 +1,9 @@
+from __future__ import annotations as _annotations
+
 from dataclasses import dataclass
 from datetime import datetime
 from functools import cache
-from typing import Literal, Union, assert_never
+from typing import Literal, assert_never
 
 from openai import AsyncClient
 from openai.types import ChatModel
@@ -18,9 +20,7 @@
 
 
 class OpenAIModel(Model):
-    def __init__(
-        self, model_name: ChatModel, *, api_key: Union[str, None] = None, client: Union[AsyncClient, None] = None
-    ):
+    def __init__(self, model_name: ChatModel, *, api_key: str | None = None, client: AsyncClient | None = None):
         if model_name not in ChatModel.__args__:
             raise ValueError(f'Invalid model name: {model_name}')
         self.model_name: ChatModel = model_name
diff --git a/pydantic_ai/result.py b/pydantic_ai/result.py
index 5f4c74d03..5cd5bb596 100644
--- a/pydantic_ai/result.py
+++ b/pydantic_ai/result.py
@@ -1,6 +1,8 @@
+from __future__ import annotations as _annotations
+
 from collections.abc import AsyncIterable
 from dataclasses import dataclass
-from typing import Any, Generic, TypedDict, TypeVar, Union
+from typing import Any, Generic, TypedDict, TypeVar
 
 from pydantic import TypeAdapter, ValidationError
 from typing_extensions import Self
@@ -65,7 +67,7 @@ class ResultSchema(Generic[ResultData]):
     _current_retry: int = 0
 
     @classmethod
-    def build(cls, response_type: type[ResultData], name: str, description: str, retries: int) -> Union[Self, None]:
+    def build(cls, response_type: type[ResultData], name: str, description: str, retries: int) -> Self | None:
         """Build a ResponseModel dataclass from a response type."""
         if response_type is str:
             return None
diff --git a/pydantic_ai/retrievers.py b/pydantic_ai/retrievers.py
index b67e4e925..81743bf63 100644
--- a/pydantic_ai/retrievers.py
+++ b/pydantic_ai/retrievers.py
@@ -47,9 +47,9 @@ class Retriever(Generic[AgentContext, P]):
     function: RetrieverFunc[AgentContext, P]
     is_async: bool
     takes_info: bool
-    single_arg_name: Union[str, None]
+    single_arg_name: str | None
     positional_fields: list[str]
-    var_positional_field: Union[str, None]
+    var_positional_field: str | None
     validator: SchemaValidator
     json_schema: _utils.ObjectJsonSchema
     max_retries: int
@@ -117,7 +117,7 @@ def _call_args(self, context: AgentContext, args_dict: dict[str, Any]) -> tuple[
         return args, args_dict
 
     def _on_error(
-        self, content: Union[list[pydantic_core.ErrorDetails], str], call_message: messages.FunctionCall
+        self, content: list[pydantic_core.ErrorDetails] | str, call_message: messages.FunctionCall
     ) -> messages.FunctionRetry:
         self._current_retry += 1
         if self._current_retry > self.max_retries:
diff --git a/pyproject.toml b/pyproject.toml
index f0a6f2943..ef61fec88 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -91,10 +91,6 @@ convention = "google"
 docstring-code-format = true
 quote-style = "single"
 
-[tool.ruff.lint.pyupgrade]
-# Preserve types, even if a file imports `from __future__ import annotations`.
-keep-runtime-typing = true
-
 [tool.pyright]
 typeCheckingMode = "strict"
 reportUnnecessaryTypeIgnoreComment = true