fix(live): propagate output token count in live API usage metadata

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

@@ -28,6 +28,8 @@
 from websockets.exceptions import ConnectionClosed
 from websockets.exceptions import ConnectionClosedOK
 
+from . import _output_schema_processor
+from . import functions
 from ...agents.base_agent import BaseAgent
 from ...agents.callback_context import CallbackContext
 from ...agents.invocation_context import InvocationContext
@@ -50,8 +52,6 @@
 from ...tools.tool_context import ToolContext
 from ...utils import model_name_utils
 from ...utils.context_utils import Aclosing
-from . import _output_schema_processor
-from . import functions
 from .audio_cache_manager import AudioCacheManager
 from .functions import build_auth_request_event
 

src/google/adk/models/gemini_llm_connection.py

@@ -217,6 +217,35 @@ def __build_full_text_response(
         live_session_id=self._gemini_session.session_id,
     )
 
+  def _to_generate_content_usage_metadata(
+      self, usage_metadata: types.UsageMetadata
+  ) -> types.GenerateContentResponseUsageMetadata:
+    """Converts live API usage metadata to GenerateContentResponse usage metadata.
+
+    The live API names output tokens `response_token_count`/
+    `response_tokens_details`, whereas `GenerateContentResponseUsageMetadata`
+    names them `candidates_token_count`/`candidates_tokens_details`.
+
+    Args:
+      usage_metadata: The live API usage metadata.
+
+    Returns:
+      The converted usage metadata.
+    """
+    return types.GenerateContentResponseUsageMetadata(
+        prompt_token_count=usage_metadata.prompt_token_count,
+        cached_content_token_count=usage_metadata.cached_content_token_count,
+        candidates_token_count=usage_metadata.response_token_count,
+        total_token_count=usage_metadata.total_token_count,
+        thoughts_token_count=usage_metadata.thoughts_token_count,
+        tool_use_prompt_token_count=usage_metadata.tool_use_prompt_token_count,
+        prompt_tokens_details=usage_metadata.prompt_tokens_details,
+        cache_tokens_details=usage_metadata.cache_tokens_details,
+        candidates_tokens_details=usage_metadata.response_tokens_details,
+        tool_use_prompt_tokens_details=usage_metadata.tool_use_prompt_tokens_details,
+        traffic_type=usage_metadata.traffic_type,
+    )
+
   async def receive(self) -> AsyncGenerator[LlmResponse, None]:
     """Receives the model response using the llm server connection.
 
@@ -235,9 +264,11 @@ async def receive(self) -> AsyncGenerator[LlmResponse, None]:
         logger.debug('Got LLM Live message: %s', message)
         live_session_id = self._gemini_session.session_id
         if message.usage_metadata:
-          # Tracks token usage data per model.
+          # Remap live token usage to GenerateContentResponse usage metadata.
           yield LlmResponse(
-              usage_metadata=message.usage_metadata,
+              usage_metadata=self._to_generate_content_usage_metadata(
+                  message.usage_metadata
+              ),
               model_version=self._model_version,
               live_session_id=live_session_id,
           )

src/google/adk/telemetry/_instrumentation.py

@@ -26,9 +26,9 @@
 from opentelemetry import trace
 import opentelemetry.context as context_api
 
-from ..events import event as event_lib
 from . import _metrics
 from . import tracing
+from ..events import event as event_lib
 
 if TYPE_CHECKING:
   from ..agents.base_agent import BaseAgent

tests/unittests/models/test_gemini_llm_connection.py

@@ -231,10 +231,12 @@ async def mock_receive_generator():
   content_response = next((r for r in responses if r.content), None)
   assert content_response is not None
 
+  # The live API's `response_token_count`/`response_tokens_details` are remapped
+  # to `candidates_token_count`/`candidates_tokens_details`.
   expected_usage = types.GenerateContentResponseUsageMetadata(
       prompt_token_count=10,
       cached_content_token_count=5,
-      candidates_token_count=None,
+      candidates_token_count=20,
       total_token_count=35,
       thoughts_token_count=2,
       prompt_tokens_details=[
@@ -243,12 +245,74 @@ async def mock_receive_generator():
       cache_tokens_details=[
           types.ModalityTokenCount(modality='text', token_count=5)
       ],
-      candidates_tokens_details=None,
+      candidates_tokens_details=[
+          types.ModalityTokenCount(modality='text', token_count=20)
+      ],
   )
   assert usage_response.usage_metadata == expected_usage
   assert content_response.content == mock_content
 
 
+async def test_receive_usage_metadata_remaps_output_tokens(
+    gemini_connection, mock_gemini_session
+):
+  """Test that live API output tokens are remapped to candidates_token_count."""
+  usage_metadata = types.UsageMetadata(
+      prompt_token_count=10,
+      cached_content_token_count=5,
+      response_token_count=20,
+      total_token_count=35,
+      thoughts_token_count=2,
+      tool_use_prompt_token_count=3,
+      prompt_tokens_details=[
+          types.ModalityTokenCount(modality='text', token_count=10)
+      ],
+      cache_tokens_details=[
+          types.ModalityTokenCount(modality='text', token_count=5)
+      ],
+      response_tokens_details=[
+          types.ModalityTokenCount(modality='text', token_count=20)
+      ],
+  )
+
+  mock_message = mock.AsyncMock()
+  mock_message.usage_metadata = usage_metadata
+  mock_message.server_content = None
+  mock_message.tool_call = None
+  mock_message.session_resumption_update = None
+  mock_message.go_away = None
+
+  async def mock_receive_generator():
+    yield mock_message
+
+  receive_mock = mock.Mock(return_value=mock_receive_generator())
+  mock_gemini_session.receive = receive_mock
+
+  responses = [resp async for resp in gemini_connection.receive()]
+
+  usage_response = next((r for r in responses if r.usage_metadata), None)
+  assert usage_response is not None
+  result = usage_response.usage_metadata
+  assert isinstance(result, types.GenerateContentResponseUsageMetadata)
+  # Output tokens are remapped from response_* to candidates_*.
+  assert result.candidates_token_count == 20
+  assert result.candidates_tokens_details == [
+      types.ModalityTokenCount(modality='text', token_count=20)
+  ]
+  # Shared fields are carried over unchanged.
+  assert result.prompt_token_count == 10
+  assert result.cached_content_token_count == 5
+  assert result.total_token_count == 35
+  assert result.thoughts_token_count == 2
+  assert result.tool_use_prompt_token_count == 3
+  assert result.prompt_tokens_details == [
+      types.ModalityTokenCount(modality='text', token_count=10)
+  ]
+  assert result.cache_tokens_details == [
+      types.ModalityTokenCount(modality='text', token_count=5)
+  ]
+
+
 async def test_receive_populates_live_session_id(
     gemini_connection, mock_gemini_session
 ):