diff --git a/src/agents/model_settings.py b/src/agents/model_settings.py
index cc4b6cb6..463104a1 100644
--- a/src/agents/model_settings.py
+++ b/src/agents/model_settings.py
@@ -39,6 +39,9 @@ class ModelSettings:
     max_tokens: int | None = None
     """The maximum number of output tokens to generate."""
 
+    reasoning_effort: Literal["low", "medium", "high"] | None = None
+    """The level of reasoning effort to use. Applies to OpenAI models."""
+
     def resolve(self, override: ModelSettings | None) -> ModelSettings:
         """Produce a new ModelSettings by overlaying any non-None values from the
         override on top of this instance."""
@@ -53,4 +56,5 @@ def resolve(self, override: ModelSettings | None) -> ModelSettings:
             parallel_tool_calls=override.parallel_tool_calls or self.parallel_tool_calls,
             truncation=override.truncation or self.truncation,
             max_tokens=override.max_tokens or self.max_tokens,
+            reasoning_effort=override.reasoning_effort or self.reasoning_effort,
         )
diff --git a/src/agents/models/openai_chatcompletions.py b/src/agents/models/openai_chatcompletions.py
index 3543225d..b00f6d7b 100644
--- a/src/agents/models/openai_chatcompletions.py
+++ b/src/agents/models/openai_chatcompletions.py
@@ -525,6 +525,7 @@ async def _fetch_response(
             tool_choice=tool_choice,
             response_format=response_format,
             parallel_tool_calls=parallel_tool_calls,
+            reasoning_effort=self._non_null_or_not_given(model_settings.reasoning_effort),
             stream=stream,
             stream_options={"include_usage": True} if stream else NOT_GIVEN,
             extra_headers=_HEADERS,
@@ -544,6 +545,7 @@ async def _fetch_response(
             else "auto",
             top_p=model_settings.top_p,
             temperature=model_settings.temperature,
+            reasoning_effort=model_settings.reasoning_effort,
             tools=[],
             parallel_tool_calls=parallel_tool_calls or False,
         )
diff --git a/src/agents/models/openai_responses.py b/src/agents/models/openai_responses.py
index 78765ecb..00562f93 100644
--- a/src/agents/models/openai_responses.py
+++ b/src/agents/models/openai_responses.py
@@ -237,6 +237,7 @@ async def _fetch_response(
             top_p=self._non_null_or_not_given(model_settings.top_p),
             truncation=self._non_null_or_not_given(model_settings.truncation),
             max_output_tokens=self._non_null_or_not_given(model_settings.max_tokens),
+            reasoning_effort=self._non_null_or_not_given(model_settings.reasoning_effort),
             tool_choice=tool_choice,
             parallel_tool_calls=parallel_tool_calls,
             stream=stream,