diff --git a/python/packages/autogen-ext/src/autogen_ext/models/openai/config/__init__.py b/python/packages/autogen-ext/src/autogen_ext/models/openai/config/__init__.py
index 02b1e3a80ff6..d0a17875875e 100644
--- a/python/packages/autogen-ext/src/autogen_ext/models/openai/config/__init__.py
+++ b/python/packages/autogen-ext/src/autogen_ext/models/openai/config/__init__.py
@@ -50,6 +50,13 @@ class CreateArguments(TypedDict, total=False):
     user: str
     stream_options: Optional[StreamOptions]
     parallel_tool_calls: Optional[bool]
+    reasoning_effort: Optional[Literal["minimal", "low", "medium", "high"]]
+    """Controls the amount of effort the model uses for reasoning.
+    Only applicable to reasoning models like o1 and o3-mini.
+    - 'minimal': Fastest response with minimal reasoning
+    - 'low': Faster responses with less reasoning
+    - 'medium': Balanced reasoning and speed
+    - 'high': More thorough reasoning, may take longer"""
 
 
 AsyncAzureADTokenProvider = Callable[[], Union[str, Awaitable[str]]]
@@ -99,6 +106,8 @@ class CreateArgumentsConfigModel(BaseModel):
     user: str | None = None
     stream_options: StreamOptions | None = None
     parallel_tool_calls: bool | None = None
+    # Controls the amount of effort the model uses for reasoning (reasoning models only)
+    reasoning_effort: Literal["minimal", "low", "medium", "high"] | None = None
 
 
 class BaseOpenAIClientConfigurationConfigModel(CreateArgumentsConfigModel):
diff --git a/python/packages/autogen-ext/tests/models/test_openai_model_client.py b/python/packages/autogen-ext/tests/models/test_openai_model_client.py
index 2c1e19521ac4..ba79795d1ed7 100644
--- a/python/packages/autogen-ext/tests/models/test_openai_model_client.py
+++ b/python/packages/autogen-ext/tests/models/test_openai_model_client.py
@@ -3269,3 +3269,112 @@ def _different_function(text: str) -> str:
 
 
 # TODO: add integration tests for Azure OpenAI using AAD token.
+
+
+@pytest.mark.asyncio
+async def test_reasoning_effort_parameter() -> None:
+    """Test that reasoning_effort parameter is properly handled in client configuration."""
+
+    # Test OpenAI client with reasoning_effort
+    openai_client = OpenAIChatCompletionClient(
+        model="gpt-5",
+        api_key="fake_key",
+        reasoning_effort="low",
+    )
+    assert openai_client._create_args["reasoning_effort"] == "low"  # pyright: ignore[reportPrivateUsage]
+
+    # Test Azure OpenAI client with reasoning_effort
+    azure_client = AzureOpenAIChatCompletionClient(
+        model="gpt-5",
+        azure_endpoint="fake_endpoint",
+        azure_deployment="gpt-5-2025-08-07",
+        api_version="2025-02-01-preview",
+        api_key="fake_key",
+        reasoning_effort="medium",
+    )
+    assert azure_client._create_args["reasoning_effort"] == "medium"  # pyright: ignore[reportPrivateUsage]
+
+    # Test load_component with reasoning_effort for OpenAI
+    from autogen_core.models import ChatCompletionClient
+
+    openai_config = {
+        "provider": "OpenAIChatCompletionClient",
+        "config": {
+            "model": "gpt-5",
+            "api_key": "fake_key",
+            "reasoning_effort": "high",
+        },
+    }
+
+    loaded_openai_client = ChatCompletionClient.load_component(openai_config)
+    assert loaded_openai_client._create_args["reasoning_effort"] == "high"  # type: ignore[attr-defined] # pyright: ignore[reportPrivateUsage, reportUnknownMemberType, reportAttributeAccessIssue]
+    assert loaded_openai_client._raw_config["reasoning_effort"] == "high"  # type: ignore[attr-defined] # pyright: ignore[reportPrivateUsage, reportUnknownMemberType, reportAttributeAccessIssue]
+
+    # Test load_component with reasoning_effort for Azure OpenAI
+    azure_config = {
+        "provider": "AzureOpenAIChatCompletionClient",
+        "config": {
+            "model": "gpt-5",
+            "azure_endpoint": "fake_endpoint",
+            "azure_deployment": "gpt-5-2025-08-07",
+            "api_version": "2025-02-01-preview",
+            "api_key": "fake_key",
+            "reasoning_effort": "low",
+        },
+    }
+
+    loaded_azure_client = ChatCompletionClient.load_component(azure_config)
+    assert loaded_azure_client._create_args["reasoning_effort"] == "low"  # type: ignore[attr-defined] # pyright: ignore[reportPrivateUsage, reportUnknownMemberType, reportAttributeAccessIssue]
+    assert loaded_azure_client._raw_config["reasoning_effort"] == "low"  # type: ignore[attr-defined] # pyright: ignore[reportPrivateUsage, reportUnknownMemberType, reportAttributeAccessIssue]
+
+    # Test serialization and deserialization
+    config_dict = openai_client.dump_component()
+    reloaded_client = OpenAIChatCompletionClient.load_component(config_dict)
+    assert reloaded_client._create_args["reasoning_effort"] == "low"  # pyright: ignore[reportPrivateUsage]
+
+
+@pytest.mark.asyncio
+async def test_reasoning_effort_validation() -> None:
+    """Test reasoning_effort parameter validation."""
+
+    # Test valid values
+    for valid_value in ["low", "medium", "high"]:
+        client = OpenAIChatCompletionClient(
+            model="gpt-5",
+            api_key="fake_key",
+            reasoning_effort=valid_value,  # type: ignore[arg-type] # pyright: ignore[reportArgumentType]
+        )
+        assert client._create_args["reasoning_effort"] == valid_value  # pyright: ignore[reportPrivateUsage]
+
+    # Test None value (should be included if explicitly set)
+    client_with_none = OpenAIChatCompletionClient(
+        model="gpt-5",
+        api_key="fake_key",
+        reasoning_effort=None,
+    )
+    # When explicitly set to None, it will be included in create_args
+    assert client_with_none._create_args["reasoning_effort"] is None  # pyright: ignore[reportPrivateUsage]
+
+    # Test not providing reasoning_effort (should not be in create_args)
+    client_without_reasoning = OpenAIChatCompletionClient(
+        model="gpt-5",
+        api_key="fake_key",
+    )
+    assert "reasoning_effort" not in client_without_reasoning._create_args  # pyright: ignore[reportPrivateUsage]
+
+    # Test invalid value via load_component (Pydantic validation)
+    from pydantic import ValidationError
+
+    with pytest.raises(ValidationError):  # Should raise ValidationError
+        from autogen_core.models import ChatCompletionClient
+
+        config = {
+            "provider": "OpenAIChatCompletionClient",
+            "config": {
+                "model": "gpt-5",
+                "api_key": "fake_key",
+                "reasoning_effort": "invalid_value",
+            },
+        }
+
+        ChatCompletionClient.load_component(config)