feat: Add reasoning content for openai model provider (strands-agents#187)

Author: xiehust

src/strands/models/openai.py

@@ -107,6 +107,13 @@ def stream(self, request: dict[str, Any]) -> Iterable[dict[str, Any]]:
             if choice.delta.content:
                 yield {"chunk_type": "content_delta", "data_type": "text", "data": choice.delta.content}
 
+            if hasattr(choice.delta, "reasoning_content") and choice.delta.reasoning_content:
+                yield {
+                    "chunk_type": "content_delta",
+                    "data_type": "reasoning_content",
+                    "data": choice.delta.reasoning_content,
+                }
+
             for tool_call in choice.delta.tool_calls or []:
                 tool_calls.setdefault(tool_call.index, []).append(tool_call)
 

src/strands/types/models/openai.py

@@ -262,6 +262,9 @@ def format_chunk(self, event: dict[str, Any]) -> StreamEvent:
                         "contentBlockDelta": {"delta": {"toolUse": {"input": event["data"].function.arguments or ""}}}
                     }
 
+                if event["data_type"] == "reasoning_content":
+                    return {"contentBlockDelta": {"delta": {"reasoningContent": {"text": event["data"]}}}}
+
                 return {"contentBlockDelta": {"delta": {"text": event["data"]}}}
 
             case "content_stop":

tests/strands/models/test_openai.py

@@ -73,31 +73,45 @@ def test_stream(openai_client, model):
     mock_tool_call_1_part_1 = unittest.mock.Mock(index=0)
     mock_tool_call_2_part_1 = unittest.mock.Mock(index=1)
     mock_delta_1 = unittest.mock.Mock(
-        content="I'll calculate", tool_calls=[mock_tool_call_1_part_1, mock_tool_call_2_part_1]
+        reasoning_content="",
+        content=None,
+        tool_calls=None,
+    )
+    mock_delta_2 = unittest.mock.Mock(
+        reasoning_content="\nI'm thinking",
+        content=None,
+        tool_calls=None,
+    )
+    mock_delta_3 = unittest.mock.Mock(
+        content="I'll calculate", tool_calls=[mock_tool_call_1_part_1, mock_tool_call_2_part_1], reasoning_content=None
     )
 
     mock_tool_call_1_part_2 = unittest.mock.Mock(index=0)
     mock_tool_call_2_part_2 = unittest.mock.Mock(index=1)
-    mock_delta_2 = unittest.mock.Mock(
-        content="that for you", tool_calls=[mock_tool_call_1_part_2, mock_tool_call_2_part_2]
+    mock_delta_4 = unittest.mock.Mock(
+        content="that for you", tool_calls=[mock_tool_call_1_part_2, mock_tool_call_2_part_2], reasoning_content=None
     )
 
-    mock_delta_3 = unittest.mock.Mock(content="", tool_calls=None)
+    mock_delta_5 = unittest.mock.Mock(content="", tool_calls=None, reasoning_content=None)
 
     mock_event_1 = unittest.mock.Mock(choices=[unittest.mock.Mock(finish_reason=None, delta=mock_delta_1)])
     mock_event_2 = unittest.mock.Mock(choices=[unittest.mock.Mock(finish_reason=None, delta=mock_delta_2)])
-    mock_event_3 = unittest.mock.Mock(choices=[unittest.mock.Mock(finish_reason="tool_calls", delta=mock_delta_3)])
-    mock_event_4 = unittest.mock.Mock()
+    mock_event_3 = unittest.mock.Mock(choices=[unittest.mock.Mock(finish_reason=None, delta=mock_delta_3)])
+    mock_event_4 = unittest.mock.Mock(choices=[unittest.mock.Mock(finish_reason=None, delta=mock_delta_4)])
+    mock_event_5 = unittest.mock.Mock(choices=[unittest.mock.Mock(finish_reason="tool_calls", delta=mock_delta_5)])
+    mock_event_6 = unittest.mock.Mock()
 
-    openai_client.chat.completions.create.return_value = iter([mock_event_1, mock_event_2, mock_event_3, mock_event_4])
+    openai_client.chat.completions.create.return_value = iter(
+        [mock_event_1, mock_event_2, mock_event_3, mock_event_4, mock_event_5, mock_event_6]
+    )
 
     request = {"model": "m1", "messages": [{"role": "user", "content": [{"type": "text", "text": "calculate 2+2"}]}]}
     response = model.stream(request)
-
     tru_events = list(response)
     exp_events = [
         {"chunk_type": "message_start"},
         {"chunk_type": "content_start", "data_type": "text"},
+        {"chunk_type": "content_delta", "data_type": "reasoning_content", "data": "\nI'm thinking"},
         {"chunk_type": "content_delta", "data_type": "text", "data": "I'll calculate"},
         {"chunk_type": "content_delta", "data_type": "text", "data": "that for you"},
         {"chunk_type": "content_stop", "data_type": "text"},
@@ -110,15 +124,15 @@ def test_stream(openai_client, model):
         {"chunk_type": "content_delta", "data_type": "tool", "data": mock_tool_call_2_part_2},
         {"chunk_type": "content_stop", "data_type": "tool"},
         {"chunk_type": "message_stop", "data": "tool_calls"},
-        {"chunk_type": "metadata", "data": mock_event_4.usage},
+        {"chunk_type": "metadata", "data": mock_event_6.usage},
     ]
 
     assert tru_events == exp_events
     openai_client.chat.completions.create.assert_called_once_with(**request)
 
 
 def test_stream_empty(openai_client, model):
-    mock_delta = unittest.mock.Mock(content=None, tool_calls=None)
+    mock_delta = unittest.mock.Mock(content=None, tool_calls=None, reasoning_content=None)
     mock_usage = unittest.mock.Mock(prompt_tokens=0, completion_tokens=0, total_tokens=0)
 
     mock_event_1 = unittest.mock.Mock(choices=[unittest.mock.Mock(finish_reason=None, delta=mock_delta)])
@@ -145,7 +159,7 @@ def test_stream_empty(openai_client, model):
 
 
 def test_stream_with_empty_choices(openai_client, model):
-    mock_delta = unittest.mock.Mock(content="content", tool_calls=None)
+    mock_delta = unittest.mock.Mock(content="content", tool_calls=None, reasoning_content=None)
     mock_usage = unittest.mock.Mock(prompt_tokens=10, completion_tokens=20, total_tokens=30)
 
     # Event with no choices attribute

tests/strands/types/models/test_openai.py

@@ -306,6 +306,11 @@ def test_format_request(model, messages, tool_specs, system_prompt):
             },
             {"contentBlockDelta": {"delta": {"toolUse": {"input": ""}}}},
         ),
+        # Content Delta - Reasoning Text
+        (
+            {"chunk_type": "content_delta", "data_type": "reasoning_content", "data": "I'm thinking"},
+            {"contentBlockDelta": {"delta": {"reasoningContent": {"text": "I'm thinking"}}}},
+        ),
         # Content Delta - Text
         (
             {"chunk_type": "content_delta", "data_type": "text", "data": "hello"},