feat: add option to include thoughts from other agents in LLM context and merge reasoning chunks

Author: lorenzbaraldi

src/google/adk/agents/run_config.py

@@ -344,6 +344,14 @@ class RunConfig(BaseModel):
       )
   """
 
+  include_thoughts_from_other_agents: bool = False
+  """Whether to include other agents' thought parts in LLM context.
+
+  By default, thoughts from other agents are excluded when their messages are
+  reformatted as user context for the current agent. Enable this only when
+  agents are expected to share internal reasoning with one another.
+  """
+
   @model_validator(mode='before')
   @classmethod
   def check_for_deprecated_save_live_audio(cls, data: Any) -> Any:

src/google/adk/flows/llm_flows/contents.py

@@ -66,6 +66,9 @@ async def run_async(
     # Preserve all contents that were added by instruction processor
     # (since llm_request.contents will be completely reassigned below)
     instruction_related_contents = llm_request.contents
+    include_thoughts_from_other_agents = (
+        invocation_context.run_config.include_thoughts_from_other_agents
+    )
 
     is_single_turn = getattr(agent, 'mode', None) == 'single_turn'
     if agent.include_contents == 'default':
@@ -78,6 +81,7 @@ async def run_async(
           isolation_scope=invocation_context.isolation_scope,
           is_single_turn=is_single_turn,
           user_content=invocation_context.user_content,
+          include_thoughts_from_other_agents=include_thoughts_from_other_agents,
       )
     else:
       # Include current turn context only (no conversation history)
@@ -89,6 +93,7 @@ async def run_async(
           isolation_scope=invocation_context.isolation_scope,
           is_single_turn=is_single_turn,
           user_content=invocation_context.user_content,
+          include_thoughts_from_other_agents=False,
       )
 
     # Add instruction-related contents to proper position in conversation
@@ -247,7 +252,9 @@ def _rearrange_events_for_latest_function_response(
   return result_events
 
 
-def _is_part_invisible(p: types.Part) -> bool:
+def _is_part_invisible(
+    p: types.Part, *, include_thoughts: bool = False
+) -> bool:
   """Returns whether a part is invisible for LLM context.
 
   A part is invisible if:
@@ -267,7 +274,7 @@ def _is_part_invisible(p: types.Part) -> bool:
   if p.function_call or p.function_response:
     return False
 
-  return p.thought or not (
+  return (p.thought and not include_thoughts) or not (
       p.text
       or p.inline_data
       or p.file_data
@@ -276,7 +283,9 @@ def _is_part_invisible(p: types.Part) -> bool:
   )
 
 
-def _contains_empty_content(event: Event) -> bool:
+def _contains_empty_content(
+    event: Event, *, include_thoughts: bool = False
+) -> bool:
   """Check if an event should be skipped due to missing or empty content.
 
   This can happen to the events that only changed session state.
@@ -298,7 +307,10 @@ def _contains_empty_content(event: Event) -> bool:
       not event.content
       or not event.content.role
       or not event.content.parts
-      or all(_is_part_invisible(p) for p in event.content.parts)
+      or all(
+          _is_part_invisible(p, include_thoughts=include_thoughts)
+          for p in event.content.parts
+      )
   ) and (not event.output_transcription and not event.input_transcription)
 
 
@@ -366,6 +378,8 @@ def _should_include_event_in_context(
     current_branch: Optional[str],
     event: Event,
     isolation_scope: Optional[str] = None,
+    *,
+    include_thoughts: bool = False,
 ) -> bool:
   """Determines if an event should be included in the LLM context.
 
@@ -391,7 +405,7 @@ def _should_include_event_in_context(
   if ev_iso != isolation_scope:
     return False
   return not (
-      _contains_empty_content(event)
+      _contains_empty_content(event, include_thoughts=include_thoughts)
       or not _is_event_belongs_to_branch(current_branch, event)
       or _is_adk_framework_event(event)
       or _is_auth_event(event)
@@ -504,6 +518,7 @@ def _get_contents(
     isolation_scope: Optional[str] = None,
     is_single_turn: bool = False,
     user_content: Optional[types.Content] = None,
+    include_thoughts_from_other_agents: bool = False,
 ) -> list[types.Content]:
   """Get the contents for the LLM request.
 
@@ -519,6 +534,8 @@ def _get_contents(
     user_content: Fallback first user turn for task agents whose
       originating delegation FC is not in session (workflow-node
       task case).
+    include_thoughts_from_other_agents: Whether to include thought parts from
+      other agents when presenting their messages as user context.
 
   Returns:
     A list of processed contents.
@@ -551,7 +568,11 @@ def _get_contents(
       e
       for e in rewind_filtered_events
       if _should_include_event_in_context(
-          current_branch, e, isolation_scope=isolation_scope
+          current_branch, e, isolation_scope=isolation_scope,
+          include_thoughts=(
+              include_thoughts_from_other_agents
+              and _is_other_agent_reply(agent_name, e)
+          )
       )
   ]
 
@@ -626,7 +647,7 @@ def _get_contents(
             break
 
     if is_other_reply:
-      if converted_event := _present_other_agent_message(event):
+      if converted_event := _present_other_agent_message(event, include_thoughts=include_thoughts_from_other_agents):
         filtered_events.append(converted_event)
     else:
       filtered_events.append(event)
@@ -677,6 +698,7 @@ def _get_current_turn_contents(
     is_single_turn: bool = False,
     isolation_scope: Optional[str] = None,
     user_content: Optional[types.Content] = None,
+    include_thoughts_from_other_agents: bool = False,
 ) -> list[types.Content]:
   """Get contents for the current turn only (no conversation history).
 
@@ -693,6 +715,8 @@ def _get_current_turn_contents(
     events: A list of all session events.
     agent_name: The name of the agent.
     preserve_function_call_ids: Whether to preserve function call ids.
+    include_thoughts_from_other_agents: Whether to include thought parts from
+      other agents when presenting their messages as user context.
 
   Returns:
     A list of contents for the current turn only, preserving context needed
@@ -702,7 +726,11 @@ def _get_current_turn_contents(
   for i in range(len(events) - 1, -1, -1):
     event = events[i]
     if _should_include_event_in_context(
-        current_branch, event, isolation_scope=isolation_scope
+        current_branch, event, isolation_scope=isolation_scope,
+        include_thoughts=(
+            include_thoughts_from_other_agents
+            and _is_other_agent_reply(agent_name, event)
+        ),
     ) and (event.author == 'user' or _is_other_agent_reply(agent_name, event)):
       return _get_contents(
           current_branch,
@@ -712,6 +740,7 @@ def _get_current_turn_contents(
           isolation_scope=isolation_scope,
           is_single_turn=is_single_turn,
           user_content=user_content,
+          include_thoughts_from_other_agents=include_thoughts_from_other_agents,
       )
 
   return []
@@ -748,14 +777,18 @@ def _is_other_agent_reply(current_agent_name: str, event: Event) -> bool:
   )
 
 
-def _present_other_agent_message(event: Event) -> Optional[Event]:
+def _present_other_agent_message(
+    event: Event, *, include_thoughts: bool = False
+) -> Optional[Event]:
   """Presents another agent's message as user context for the current agent.
 
   Reformats the event with role='user' and adds '[agent_name] said:' prefix
   to provide context without confusion about authorship.
 
   Args:
     event: The event from another agent to present as context.
+    include_thoughts: Whether to include thought parts as explicit text
+      context.
 
   Returns:
     Event reformatted as user-role context with agent attribution, or None
@@ -769,7 +802,10 @@ def _present_other_agent_message(event: Event) -> Optional[Event]:
   content.parts = [types.Part(text='For context:')]
   for part in event.content.parts:
     if part.thought:
-      # Exclude thoughts from the context.
+      if include_thoughts and part.text is not None and part.text.strip():
+        content.parts.append(
+            types.Part(text=f'[{event.author}] thought: {part.text}')
+        )
       continue
     elif part.text is not None and part.text.strip():
       content.parts.append(

src/google/adk/models/lite_llm.py

@@ -718,6 +718,28 @@ def _extract_reasoning_tokens(usage: Any) -> int:
   return 0
 
 
+def _merge_reasoning_texts(reasoning_parts: Iterable[types.Part]) -> str:
+  """Merges reasoning text fragments into a single provider payload.
+
+  Streaming providers such as vLLM can emit reasoning as token-sized chunks.
+  ADK stores those chunks as consecutive thought parts, so inserting separators
+  here changes the model's original reasoning text.
+  """
+  reasoning_texts = []
+  for part in reasoning_parts:
+    if part.text:
+      reasoning_texts.append(part.text)
+    elif (
+        part.inline_data
+        and part.inline_data.data
+        and part.inline_data.mime_type
+        and part.inline_data.mime_type.startswith("text/")
+    ):
+      reasoning_texts.append(_decode_inline_text_data(part.inline_data.data))
+
+  return "".join(reasoning_texts)
+
+
 def _extract_thought_signature_from_tool_call(
     tool_call: ChatCompletionMessageToolCall,
 ) -> Optional[bytes]:
@@ -919,19 +941,7 @@ async def _content_to_message_param(
         msg["thinking_blocks"] = thinking_blocks  # type: ignore[typeddict-unknown-key]
         return msg
 
-    reasoning_texts = []
-    for part in reasoning_parts:
-      if part.text:
-        reasoning_texts.append(part.text)
-      elif (
-          part.inline_data
-          and part.inline_data.data
-          and part.inline_data.mime_type
-          and part.inline_data.mime_type.startswith("text/")
-      ):
-        reasoning_texts.append(_decode_inline_text_data(part.inline_data.data))
-
-    reasoning_content = _NEW_LINE.join(text for text in reasoning_texts if text)
+    reasoning_content = _merge_reasoning_texts(reasoning_parts)
     return ChatCompletionAssistantMessage(
         role=role,
         content=final_content,

tests/unittests/flows/llm_flows/test_contents_other_agent.py

@@ -15,6 +15,7 @@
 """Behavioral tests for other agent message processing in contents module."""
 
 from google.adk.agents.llm_agent import Agent
+from google.adk.agents.run_config import RunConfig
 from google.adk.events.event import Event
 from google.adk.flows.llm_flows.contents import request_processor
 from google.adk.models.llm_request import LlmRequest
@@ -85,6 +86,111 @@ async def test_other_agent_thoughts_are_excluded():
   ]
 
 
+@pytest.mark.asyncio
+async def test_other_agent_thoughts_can_be_included_as_context():
+  """Test opt-in inclusion of thoughts from other agents."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent,
+      run_config=RunConfig(include_thoughts_from_other_agents=True),
+  )
+  other_agent_event = Event(
+      invocation_id="test_inv",
+      author="other_agent",
+      content=types.ModelContent([
+          types.Part(text="Public message", thought=False),
+          types.Part(text="Private thought", thought=True),
+          types.Part(text="Another public message"),
+      ]),
+  )
+  invocation_context.session.events = [other_agent_event]
+
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  assert llm_request.contents[0].role == "user"
+  assert llm_request.contents[0].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[other_agent] said: Public message"),
+      types.Part(text="[other_agent] thought: Private thought"),
+      types.Part(text="[other_agent] said: Another public message"),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_other_agent_thought_only_message_can_be_included_as_context():
+  """Test opt-in inclusion of thought-only messages from other agents."""
+  agent = Agent(model="gemini-2.5-flash", name="current_agent")
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent,
+      run_config=RunConfig(include_thoughts_from_other_agents=True),
+  )
+  other_agent_event = Event(
+      invocation_id="test_inv",
+      author="other_agent",
+      content=types.ModelContent([
+          types.Part(text="First private thought", thought=True),
+          types.Part(text="Second private thought", thought=True),
+      ]),
+  )
+  invocation_context.session.events = [other_agent_event]
+
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  assert llm_request.contents[0].role == "user"
+  assert llm_request.contents[0].parts == [
+      types.Part(text="For context:"),
+      types.Part(text="[other_agent] thought: First private thought"),
+      types.Part(text="[other_agent] thought: Second private thought"),
+  ]
+
+
+@pytest.mark.asyncio
+async def test_other_agent_thoughts_excluded_from_current_turn_only_context():
+  """Test include_contents='none' does not include other-agent thoughts."""
+  agent = Agent(
+      model="gemini-2.5-flash",
+      name="current_agent",
+      include_contents="none",
+  )
+  llm_request = LlmRequest(model="gemini-2.5-flash")
+  invocation_context = await testing_utils.create_invocation_context(
+      agent=agent,
+      run_config=RunConfig(include_thoughts_from_other_agents=True),
+  )
+  invocation_context.session.events = [
+      Event(
+          invocation_id="inv1",
+          author="user",
+          content=types.UserContent("Earlier user message"),
+      ),
+      Event(
+          invocation_id="inv2",
+          author="other_agent",
+          content=types.ModelContent([
+              types.Part(text="Private thought", thought=True),
+              types.Part(text="Visible handoff"),
+          ]),
+      ),
+  ]
+
+  async for _ in request_processor.run_async(invocation_context, llm_request):
+    pass
+
+  assert llm_request.contents == [
+      types.Content(
+          role="user",
+          parts=[
+              types.Part(text="For context:"),
+              types.Part(text="[other_agent] said: Visible handoff"),
+          ],
+      )
+  ]
+
+
 @pytest.mark.asyncio
 async def test_other_agent_function_calls():
   """Test that function calls from other agents are preserved in context."""