fix(core): include llm_output in streaming LLMResult

libs/core/langchain_core/language_models/chat_models.py

@@ -204,7 +204,8 @@ def generate_from_stream(stream: Iterator[ChatGenerationChunk]) -> ChatResult:
                 message=message_chunk_to_message(generation.message),
                 generation_info=generation.generation_info,
             )
-        ]
+        ],
+        llm_output={},
     )
 
 
@@ -596,7 +597,7 @@ def stream(
                 run_manager.on_llm_error(err, response=LLMResult(generations=[]))
                 raise err
 
-            run_manager.on_llm_end(LLMResult(generations=[[generation]]))
+            run_manager.on_llm_end(LLMResult(generations=[[generation]], llm_output={}))
 
     @override
     async def astream(
@@ -725,7 +726,7 @@ async def astream(
             raise err
 
         await run_manager.on_llm_end(
-            LLMResult(generations=[[generation]]),
+            LLMResult(generations=[[generation]], llm_output={}),
         )
 
     # --- Custom methods ---
@@ -1148,7 +1149,7 @@ def _generate_with_cache(
                 cache_val = llm_cache.lookup(prompt, llm_string)
                 if isinstance(cache_val, list):
                     converted_generations = self._convert_cached_generations(cache_val)
-                    return ChatResult(generations=converted_generations)
+                    return ChatResult(generations=converted_generations, llm_output={})
             elif self.cache is None:
                 pass
             else:
@@ -1266,7 +1267,7 @@ async def _agenerate_with_cache(
                 cache_val = await llm_cache.alookup(prompt, llm_string)
                 if isinstance(cache_val, list):
                     converted_generations = self._convert_cached_generations(cache_val)
-                    return ChatResult(generations=converted_generations)
+                    return ChatResult(generations=converted_generations, llm_output={})
             elif self.cache is None:
                 pass
             else:
@@ -1722,7 +1723,7 @@ def _generate(
         output_str = self._call(messages, stop=stop, run_manager=run_manager, **kwargs)
         message = AIMessage(content=output_str)
         generation = ChatGeneration(message=message)
-        return ChatResult(generations=[generation])
+        return ChatResult(generations=[generation], llm_output={})
 
     @abstractmethod
     def _call(

libs/core/langchain_core/language_models/fake_chat_models.py

@@ -44,7 +44,7 @@ def _generate(
         else:
             self.i = 0
         generation = ChatGeneration(message=response)
-        return ChatResult(generations=[generation])
+        return ChatResult(generations=[generation], llm_output={})
 
     @property
     @override
@@ -261,7 +261,7 @@ def _generate(
         message = next(self.messages)
         message_ = AIMessage(content=message) if isinstance(message, str) else message
         generation = ChatGeneration(message=message_)
-        return ChatResult(generations=[generation])
+        return ChatResult(generations=[generation], llm_output={})
 
     def _stream(
         self,
@@ -386,7 +386,9 @@ def _generate(
         run_manager: CallbackManagerForLLMRun | None = None,
         **kwargs: Any,
     ) -> ChatResult:
-        return ChatResult(generations=[ChatGeneration(message=messages[-1])])
+        return ChatResult(
+            generations=[ChatGeneration(message=messages[-1])], llm_output={}
+        )
 
     @property
     def _llm_type(self) -> str:

libs/core/langchain_core/language_models/llms.py

@@ -564,7 +564,7 @@ def stream(
                 run_manager.on_llm_error(err, response=LLMResult(generations=[]))
                 raise err
 
-            run_manager.on_llm_end(LLMResult(generations=[[generation]]))
+            run_manager.on_llm_end(LLMResult(generations=[[generation]], llm_output={}))
 
     @override
     async def astream(
@@ -635,7 +635,9 @@ async def astream(
             await run_manager.on_llm_error(err, response=LLMResult(generations=[]))
             raise err
 
-        await run_manager.on_llm_end(LLMResult(generations=[[generation]]))
+        await run_manager.on_llm_end(
+            LLMResult(generations=[[generation]], llm_output={})
+        )
 
     # --- Custom methods ---
 
@@ -1502,7 +1504,7 @@ def _generate(
                 else self._call(prompt, stop=stop, **kwargs)
             )
             generations.append([Generation(text=text)])
-        return LLMResult(generations=generations)
+        return LLMResult(generations=generations, llm_output={})
 
     async def _agenerate(
         self,
@@ -1520,4 +1522,4 @@ async def _agenerate(
                 else await self._acall(prompt, stop=stop, **kwargs)
             )
             generations.append([Generation(text=text)])
-        return LLMResult(generations=generations)
+        return LLMResult(generations=generations, llm_output={})

libs/core/tests/unit_tests/fake/test_fake_chat_model.py

@@ -7,15 +7,15 @@
 
 from typing_extensions import override
 
-from langchain_core.callbacks.base import AsyncCallbackHandler
+from langchain_core.callbacks.base import AsyncCallbackHandler, BaseCallbackHandler
 from langchain_core.language_models import (
     FakeListChatModel,
     FakeMessagesListChatModel,
     GenericFakeChatModel,
     ParrotFakeChatModel,
 )
 from langchain_core.messages import AIMessage, AIMessageChunk, BaseMessage, HumanMessage
-from langchain_core.outputs import ChatGenerationChunk, GenerationChunk
+from langchain_core.outputs import ChatGenerationChunk, GenerationChunk, LLMResult
 from tests.unit_tests.stubs import (
     _any_id_ai_message,
     _any_id_ai_message_chunk,
@@ -253,3 +253,43 @@ def test_fake_messages_list_chat_model_sleep_delay() -> None:
     elapsed = time.time() - start
 
     assert elapsed >= sleep_time
+
+
+def test_stream_llm_result_contains_llm_output() -> None:
+    """Test that streaming mode includes llm_output in LLMResult."""
+
+    class LLMResultCaptureHandler(BaseCallbackHandler):
+        """Callback handler that captures LLMResult from on_llm_end."""
+
+        def __init__(self) -> None:
+            self.llm_results: list[LLMResult] = []
+
+        @override
+        def on_llm_end(
+            self,
+            response: LLMResult,
+            *,
+            run_id: UUID,
+            parent_run_id: UUID | None = None,
+            **kwargs: Any,
+        ) -> None:
+            """Capture the LLMResult."""
+            self.llm_results.append(response)
+
+    model = GenericFakeChatModel(messages=cycle([AIMessage(content="hello world")]))
+    handler = LLMResultCaptureHandler()
+
+    # Consume the stream to trigger on_llm_end
+    chunks = list(model.stream("test", config={"callbacks": [handler]}))
+
+    # Verify we got chunks
+    assert len(chunks) > 0
+
+    # Verify on_llm_end was called
+    assert len(handler.llm_results) == 1
+
+    # Verify llm_output field exists in the LLMResult
+    llm_result = handler.llm_results[0]
+    assert hasattr(llm_result, "llm_output")
+    assert llm_result.llm_output is not None
+    assert isinstance(llm_result.llm_output, dict)

libs/core/tests/unit_tests/runnables/test_runnable_events_v1.py

@@ -648,7 +648,7 @@ def i_dont_stream(value: Any, config: RunnableConfig) -> Any:
                                 }
                             ]
                         ],
-                        "llm_output": None,
+                        "llm_output": {},
                         "run": None,
                         "type": "LLMResult",
                     },
@@ -780,7 +780,7 @@ async def ai_dont_stream(value: Any, config: RunnableConfig) -> Any:
                                 }
                             ]
                         ],
-                        "llm_output": None,
+                        "llm_output": {},
                         "run": None,
                         "type": "LLMResult",
                     },
@@ -1030,7 +1030,7 @@ async def test_event_stream_with_simple_chain() -> None:
                                 }
                             ]
                         ],
-                        "llm_output": None,
+                        "llm_output": {},
                         "run": None,
                         "type": "LLMResult",
                     },
@@ -1809,7 +1809,7 @@ async def test_with_llm() -> None:
                                 }
                             ]
                         ],
-                        "llm_output": None,
+                        "llm_output": {},
                         "run": None,
                         "type": "LLMResult",
                     },