diff --git a/src/google/adk/live/_runner_utils.py b/src/google/adk/live/_runner_utils.py
index fecb48375fc..7a8415dd2d6 100644
--- a/src/google/adk/live/_runner_utils.py
+++ b/src/google/adk/live/_runner_utils.py
@@ -19,6 +19,7 @@
 import asyncio
 from contextlib import aclosing
 import logging
+from typing import Any
 from typing import AsyncGenerator
 from typing import Optional
 from typing import TYPE_CHECKING
@@ -52,16 +53,20 @@ def new_invocation_context_for_live(
   run_config = run_config or RunConfig()
 
   # For live multi-agents system, we need model's text transcription as
-  # context for the transferred agent.
+  # context for the transferred agent. Only fill the defaults when the caller
+  # did not set the fields explicitly, so an explicit None stays disabled.
   if hasattr(runner.agent, "sub_agents") and runner.agent.sub_agents:
+    updates: dict[str, Any] = {}
     if (
         run_config.response_modalities
         and types.Modality.AUDIO in run_config.response_modalities
+        and "output_audio_transcription" not in run_config.model_fields_set
     ):
-      if not run_config.output_audio_transcription:
-        run_config.output_audio_transcription = types.AudioTranscriptionConfig()
-    if not run_config.input_audio_transcription:
-      run_config.input_audio_transcription = types.AudioTranscriptionConfig()
+      updates["output_audio_transcription"] = types.AudioTranscriptionConfig()
+    if "input_audio_transcription" not in run_config.model_fields_set:
+      updates["input_audio_transcription"] = types.AudioTranscriptionConfig()
+    if updates:
+      run_config = run_config.model_copy(update=updates)
   return runner._new_invocation_context(  # pylint: disable=protected-access
       session,
       live_request_queue=live_request_queue,
diff --git a/tests/unittests/live/test__runner_utils.py b/tests/unittests/live/test__runner_utils.py
index 59cff7c727f..85a358f9613 100644
--- a/tests/unittests/live/test__runner_utils.py
+++ b/tests/unittests/live/test__runner_utils.py
@@ -85,6 +85,87 @@ async def test_new_invocation_context_for_live_subagents_audio_transcription():
   assert ic.run_config.input_audio_transcription is not None
 
 
+def _multi_agent_runner() -> Runner:
+  parent_agent = _MockLiveAgent(name="parent")
+  parent_agent.sub_agents = [_MockLiveAgent(name="child")]
+  return Runner(
+      app_name="test_app",
+      agent=parent_agent,
+      session_service=InMemorySessionService(),
+  )
+
+
+@pytest.mark.asyncio
+async def test_new_invocation_context_for_live_respects_explicit_opt_out():
+  runner = _multi_agent_runner()
+  session = await runner.session_service.create_session(
+      user_id="u1", session_id="s1", app_name=runner.app_name
+  )
+  run_config = RunConfig(
+      response_modalities=[types.Modality.AUDIO],
+      output_audio_transcription=None,
+      input_audio_transcription=None,
+  )
+
+  ic = _runner_utils.new_invocation_context_for_live(
+      runner,
+      session,
+      live_request_queue=LiveRequestQueue(),
+      run_config=run_config,
+  )
+
+  assert ic.run_config.output_audio_transcription is None
+  assert ic.run_config.input_audio_transcription is None
+  # The caller's config object must not be mutated either.
+  assert run_config.output_audio_transcription is None
+  assert run_config.input_audio_transcription is None
+
+
+@pytest.mark.asyncio
+async def test_new_invocation_context_for_live_opt_out_without_modalities():
+  runner = _multi_agent_runner()
+  session = await runner.session_service.create_session(
+      user_id="u1", session_id="s1", app_name=runner.app_name
+  )
+  run_config = RunConfig(input_audio_transcription=None)
+
+  ic = _runner_utils.new_invocation_context_for_live(
+      runner,
+      session,
+      live_request_queue=LiveRequestQueue(),
+      run_config=run_config,
+  )
+
+  assert ic.run_config.input_audio_transcription is None
+
+
+@pytest.mark.asyncio
+async def test_new_invocation_context_for_live_without_subagents_passthrough():
+  runner = Runner(
+      app_name="test_app",
+      agent=_MockLiveAgent(name="solo"),
+      session_service=InMemorySessionService(),
+  )
+  session = await runner.session_service.create_session(
+      user_id="u1", session_id="s1", app_name=runner.app_name
+  )
+  run_config = RunConfig(
+      response_modalities=[types.Modality.AUDIO],
+      output_audio_transcription=None,
+      input_audio_transcription=None,
+  )
+
+  ic = _runner_utils.new_invocation_context_for_live(
+      runner,
+      session,
+      live_request_queue=LiveRequestQueue(),
+      run_config=run_config,
+  )
+
+  assert ic.run_config.output_audio_transcription is None
+  assert ic.run_config.input_audio_transcription is None
+
+
 @pytest.mark.asyncio
 async def test_run_live_validates_required_arguments():
   agent = _MockLiveAgent()