Add reasoning parameter to ModelSettings (#388)

fixes #189 

@rm-openai Would really appreciate if this can get a quick review.

---------

Co-authored-by: Rohan Mehta <rm@openai.com>

src/agents/model_settings.py

@@ -3,6 +3,8 @@ from __future__ import annotations
 from dataclasses import dataclass, fields, replace
 from typing import Literal
 
+from openai.types.shared import Reasoning
+
 
 @dataclass
 class ModelSettings:
@@ -40,6 +42,11 @@ class ModelSettings:
     max_tokens: int | None = None
     """The maximum number of output tokens to generate."""
 
+    reasoning: Reasoning | None = None
+    """Configuration options for
+    [reasoning models](https://platform.openai.com/docs/guides/reasoning).
+    """
+
     metadata: dict[str, str] | None = None
     """Metadata to include with the model response call."""
 

src/agents/models/openai_chatcompletions.py

@@ -521,6 +521,8 @@ class OpenAIChatCompletionsModel(Model):
         # Match the behavior of Responses where store is True when not given
         store = model_settings.store if model_settings.store is not None else True
 
+        reasoning_effort = model_settings.reasoning.effort if model_settings.reasoning else None
+
         ret = await self._get_client().chat.completions.create(
             model=self.model,
             messages=converted_messages,
@@ -536,6 +538,7 @@ class OpenAIChatCompletionsModel(Model):
             stream=stream,
             stream_options={"include_usage": True} if stream else NOT_GIVEN,
             store=store,
+            reasoning_effort=self._non_null_or_not_given(reasoning_effort),
             extra_headers=_HEADERS,
             metadata=model_settings.metadata,
         )
@@ -556,6 +559,7 @@ class OpenAIChatCompletionsModel(Model):
             temperature=model_settings.temperature,
             tools=[],
             parallel_tool_calls=parallel_tool_calls or False,
+            reasoning=model_settings.reasoning,
         )
         return response, ret
 

src/agents/models/openai_responses.py

@@ -247,6 +247,7 @@ class OpenAIResponsesModel(Model):
             extra_headers=_HEADERS,
             text=response_format,
             store=self._non_null_or_not_given(model_settings.store),
+            reasoning=self._non_null_or_not_given(model_settings.reasoning),
             metadata=model_settings.metadata,
         )