diff --git a/src/pipecat/frames/frames.py b/src/pipecat/frames/frames.py
index decb76d75..17ab94695 100644
--- a/src/pipecat/frames/frames.py
+++ b/src/pipecat/frames/frames.py
@@ -1439,6 +1439,27 @@ class STTMetadataFrame(ServiceMetadataFrame):
     ttfs_p99_latency: float
 
 
+@dataclass
+class RealtimeServiceMetadataFrame(ServiceMetadataFrame):
+    """Metadata announcing a realtime (speech-to-speech) LLM service.
+
+    Broadcast by realtime LLM services at pipeline start so downstream
+    processors — notably ``LLMContextAggregatorPair`` — can detect that
+    a realtime service is in the pipeline. The aggregator uses this to
+    surface a one-time recommendation to opt in to
+    ``RealtimeServiceModeConfig`` when it hasn't been configured.
+
+    Parameters:
+        emits_user_turn_frames: Whether this service emits
+            ``UserStartedSpeakingFrame`` / ``UserStoppedSpeakingFrame``
+            from server-side turn signals. False for services with no
+            server-side turn signals (e.g. Gemini Live, AWS Nova Sonic,
+            Ultravox).
+    """
+
+    emits_user_turn_frames: bool = True
+
+
 @dataclass
 class ServiceSwitcherRequestMetadataFrame(ControlFrame):
     """Request a service to re-emit its metadata frames.
diff --git a/src/pipecat/services/aws/nova_sonic/llm.py b/src/pipecat/services/aws/nova_sonic/llm.py
index 4aeb5c848..2e6aab9ca 100644
--- a/src/pipecat/services/aws/nova_sonic/llm.py
+++ b/src/pipecat/services/aws/nova_sonic/llm.py
@@ -56,7 +56,7 @@ from pipecat.services.aws.nova_sonic.session_continuation import (
     SessionContinuationHelper,
     SessionContinuationParams,
 )
-from pipecat.services.llm_service import LLMService
+from pipecat.services.llm_service import LLMService, RealtimeServiceInfo
 from pipecat.services.settings import NOT_GIVEN, LLMSettings, _NotGiven, assert_given
 from pipecat.utils.time import time_now_iso8601
 
@@ -249,6 +249,10 @@ class AWSNovaSonicLLMService(LLMService[AWSNovaSonicLLMAdapter]):
     # Override the default adapter to use the AWSNovaSonicLLMAdapter one
     adapter_class = AWSNovaSonicLLMAdapter
 
+    # Realtime (speech-to-speech) service. Does NOT emit
+    # UserStarted/StoppedSpeakingFrame from server-side turn signals.
+    _realtime_service_info = RealtimeServiceInfo(emits_user_turn_frames=False)
+
     def __init__(
         self,
         *,
diff --git a/src/pipecat/services/google/gemini_live/llm.py b/src/pipecat/services/google/gemini_live/llm.py
index 7194127b1..80d722d29 100644
--- a/src/pipecat/services/google/gemini_live/llm.py
+++ b/src/pipecat/services/google/gemini_live/llm.py
@@ -62,7 +62,7 @@ from pipecat.processors.aggregators.llm_context import LLMContext, LLMSpecificMe
 from pipecat.processors.frame_processor import FrameDirection
 from pipecat.services.google.frames import LLMSearchOrigin, LLMSearchResponseFrame, LLMSearchResult
 from pipecat.services.google.utils import update_google_client_http_options
-from pipecat.services.llm_service import FunctionCallFromLLM, LLMService
+from pipecat.services.llm_service import FunctionCallFromLLM, LLMService, RealtimeServiceInfo
 from pipecat.services.settings import NOT_GIVEN, LLMSettings, _NotGiven, assert_given
 from pipecat.transcriptions.language import Language, resolve_language
 from pipecat.utils.string import match_endofsentence
@@ -369,6 +369,11 @@ class GeminiLiveLLMService(LLMService[GeminiLLMAdapter]):
     # Overriding the default adapter to use the Gemini one.
     adapter_class = GeminiLLMAdapter
 
+    # Realtime (speech-to-speech) service. Does NOT emit
+    # UserStarted/StoppedSpeakingFrame from server-side turn signals —
+    # the API exposes an `interrupted` event but no turn-start/-end.
+    _realtime_service_info = RealtimeServiceInfo(emits_user_turn_frames=False)
+
     @property
     def _is_gemini_3(self) -> bool:
         """Check if the current model is a Gemini 3.x model."""
diff --git a/src/pipecat/services/inworld/realtime/llm.py b/src/pipecat/services/inworld/realtime/llm.py
index 023e09fbc..352e669e4 100644
--- a/src/pipecat/services/inworld/realtime/llm.py
+++ b/src/pipecat/services/inworld/realtime/llm.py
@@ -51,7 +51,7 @@ from pipecat.metrics.metrics import LLMTokenUsage
 from pipecat.processors.aggregators import async_tool_messages
 from pipecat.processors.aggregators.llm_context import LLMContext, LLMSpecificMessage
 from pipecat.processors.frame_processor import FrameDirection
-from pipecat.services.llm_service import FunctionCallFromLLM, LLMService
+from pipecat.services.llm_service import FunctionCallFromLLM, LLMService, RealtimeServiceInfo
 from pipecat.services.settings import (
     NOT_GIVEN,
     LLMSettings,
@@ -245,6 +245,10 @@ class InworldRealtimeLLMService(LLMService[InworldRealtimeLLMAdapter]):
 
     adapter_class = InworldRealtimeLLMAdapter
 
+    # Realtime (speech-to-speech) service. Emits UserStarted/Stopped
+    # speaking frames from server-side VAD events.
+    _realtime_service_info = RealtimeServiceInfo(emits_user_turn_frames=True)
+
     # Target ~60ms audio chunks when sending to Inworld (16-bit mono).
     _AUDIO_CHUNK_TARGET_MS = 60
 
diff --git a/src/pipecat/services/llm_service.py b/src/pipecat/services/llm_service.py
index 58ed54bd0..eb01d26fc 100644
--- a/src/pipecat/services/llm_service.py
+++ b/src/pipecat/services/llm_service.py
@@ -16,6 +16,7 @@ from collections.abc import Awaitable, Callable, Mapping, Sequence
 from dataclasses import dataclass
 from typing import (
     Any,
+    ClassVar,
     Generic,
     Protocol,
     cast,
@@ -48,6 +49,7 @@ from pipecat.frames.frames import (
     LLMFullResponseStartFrame,
     LLMTextFrame,
     LLMUpdateSettingsFrame,
+    RealtimeServiceMetadataFrame,
     StartFrame,
 )
 from pipecat.processors.aggregators.llm_context import (
@@ -97,6 +99,31 @@ class FunctionCallResultCallback(Protocol):
         ...
 
 
+@dataclass(frozen=True)
+class RealtimeServiceInfo:
+    """Per-service metadata for realtime (speech-to-speech) LLM services.
+
+    Realtime LLM subclasses set ``LLMService._realtime_service_info`` to a
+    populated instance; the presence of a non-None value is what marks a
+    service as realtime. Non-realtime services keep the default ``None``.
+
+    Carries the configuration ``LLMService`` and
+    ``LLMContextAggregatorPair`` need to wire up realtime behavior:
+    auto-broadcasting ``RealtimeServiceMetadataFrame`` at start, the
+    startup INFO log for services with no server-side turn signals, and
+    the aggregator's one-time recommendation log.
+
+    Parameters:
+        emits_user_turn_frames: Whether the service emits
+            ``UserStartedSpeakingFrame`` / ``UserStoppedSpeakingFrame``
+            from server-side turn signals. False for services with no
+            server-side turn signals (e.g. Gemini Live, AWS Nova Sonic,
+            Ultravox).
+    """
+
+    emits_user_turn_frames: bool = True
+
+
 @dataclass
 class FunctionCallParams:
     """Parameters for a function call.
@@ -244,6 +271,15 @@ class LLMService(UserTurnCompletionLLMServiceMixin, AIService, Generic[TAdapter]
     # However, subclasses should override this with a more specific adapter when necessary.
     adapter_class: type[BaseLLMAdapter] = OpenAILLMAdapter
 
+    # Marker + per-service config for realtime (speech-to-speech) LLM
+    # services. Realtime subclasses override this with a populated
+    # ``RealtimeServiceInfo`` instance — the presence of a non-None value
+    # is what marks the service as realtime. Non-realtime services keep
+    # the default ``None`` and the realtime-specific machinery
+    # (auto-broadcast of ``RealtimeServiceMetadataFrame``, startup INFO
+    # log for services without server-side turn signals) stays inert.
+    _realtime_service_info: ClassVar[RealtimeServiceInfo | None] = None
+
     # Returned to the LLM as the tool result when an unavailable function is
     # called. Deliberately neutral about future availability so the LLM can
     # pick the function up again if it returns (e.g. via the
@@ -363,6 +399,21 @@ class LLMService(UserTurnCompletionLLMServiceMixin, AIService, Generic[TAdapter]
             await self._create_sequential_runner_task()
         if self._enable_async_tool_cancellation and self._has_async_tools():
             self._setup_async_tool_cancellation()
+        if (
+            self._realtime_service_info is not None
+            and not self._realtime_service_info.emits_user_turn_frames
+        ):
+            logger.info(
+                f"{self} does not emit UserStartedSpeakingFrame/"
+                "UserStoppedSpeakingFrame. Pipeline processors that depend on "
+                "these frames (RTVI client speech events, TurnTrackingObserver, "
+                "AudioBufferProcessor turn recording, UserIdleController, user "
+                "mute strategies, voicemail detector) will not activate. To "
+                "produce them locally, add `vad_analyzer=` to "
+                "LLMUserAggregatorParams. Note: local turn detection is a "
+                "heuristic; its boundaries may not match the provider's actual "
+                "server-side turn decisions and can desynchronize in subtle ways."
+            )
 
     async def stop(self, frame: EndFrame):
         """Stop the LLM service.
@@ -495,6 +546,23 @@ class LLMService(UserTurnCompletionLLMServiceMixin, AIService, Generic[TAdapter]
 
         await super().push_frame(frame, direction)
 
+        # Broadcast realtime-service metadata immediately after the
+        # StartFrame propagates downstream, mirroring the order STT
+        # services use for STTMetadataFrame. The aggregator (upstream)
+        # already received its own StartFrame and is ready to process
+        # the broadcast; downstream processors see StartFrame then the
+        # metadata in their queues.
+        if (
+            self._realtime_service_info is not None
+            and isinstance(frame, StartFrame)
+            and direction == FrameDirection.DOWNSTREAM
+        ):
+            await self.broadcast_frame(
+                RealtimeServiceMetadataFrame,
+                service_name=self.name,
+                emits_user_turn_frames=self._realtime_service_info.emits_user_turn_frames,
+            )
+
     async def _push_llm_text(self, text: str):
         """Push LLM text, using turn completion detection if enabled.
 
diff --git a/src/pipecat/services/openai/realtime/llm.py b/src/pipecat/services/openai/realtime/llm.py
index 19fa0f717..9ce78ab89 100644
--- a/src/pipecat/services/openai/realtime/llm.py
+++ b/src/pipecat/services/openai/realtime/llm.py
@@ -51,7 +51,7 @@ from pipecat.metrics.metrics import LLMTokenUsage
 from pipecat.processors.aggregators import async_tool_messages
 from pipecat.processors.aggregators.llm_context import LLMContext, LLMSpecificMessage
 from pipecat.processors.frame_processor import FrameDirection
-from pipecat.services.llm_service import FunctionCallFromLLM, LLMService
+from pipecat.services.llm_service import FunctionCallFromLLM, LLMService, RealtimeServiceInfo
 from pipecat.services.openai._constants import OPENAI_REALTIME_WHISPER_MODEL, OPENAI_SAMPLE_RATE
 from pipecat.services.settings import (
     NOT_GIVEN,
@@ -212,6 +212,10 @@ class OpenAIRealtimeLLMService(LLMService[OpenAIRealtimeLLMAdapter]):
     # Overriding the default adapter to use the OpenAIRealtimeLLMAdapter one.
     adapter_class = OpenAIRealtimeLLMAdapter
 
+    # Realtime (speech-to-speech) service. Emits UserStarted/Stopped
+    # speaking frames from server-side VAD events.
+    _realtime_service_info = RealtimeServiceInfo(emits_user_turn_frames=True)
+
     def __init__(
         self,
         *,
diff --git a/src/pipecat/services/ultravox/llm.py b/src/pipecat/services/ultravox/llm.py
index 74735df6b..91aa66486 100644
--- a/src/pipecat/services/ultravox/llm.py
+++ b/src/pipecat/services/ultravox/llm.py
@@ -48,7 +48,7 @@ from pipecat.frames.frames import (
 from pipecat.processors.aggregators import async_tool_messages
 from pipecat.processors.aggregators.llm_context import LLMContext, LLMSpecificMessage
 from pipecat.processors.frame_processor import FrameDirection
-from pipecat.services.llm_service import FunctionCallFromLLM, LLMService
+from pipecat.services.llm_service import FunctionCallFromLLM, LLMService, RealtimeServiceInfo
 from pipecat.services.settings import NOT_GIVEN, LLMSettings, _NotGiven, assert_given
 from pipecat.utils.time import time_now_iso8601
 
@@ -179,6 +179,10 @@ class UltravoxRealtimeLLMService(LLMService):
     Settings = UltravoxRealtimeLLMSettings
     _settings: Settings
 
+    # Realtime (speech-to-speech) service. Does NOT emit
+    # UserStarted/StoppedSpeakingFrame from server-side turn signals.
+    _realtime_service_info = RealtimeServiceInfo(emits_user_turn_frames=False)
+
     def __init__(
         self,
         *,
diff --git a/src/pipecat/services/xai/realtime/llm.py b/src/pipecat/services/xai/realtime/llm.py
index 7ac83d071..cbfdbaf61 100644
--- a/src/pipecat/services/xai/realtime/llm.py
+++ b/src/pipecat/services/xai/realtime/llm.py
@@ -50,7 +50,7 @@ from pipecat.metrics.metrics import LLMTokenUsage
 from pipecat.processors.aggregators import async_tool_messages
 from pipecat.processors.aggregators.llm_context import LLMContext, LLMSpecificMessage
 from pipecat.processors.frame_processor import FrameDirection
-from pipecat.services.llm_service import FunctionCallFromLLM, LLMService
+from pipecat.services.llm_service import FunctionCallFromLLM, LLMService, RealtimeServiceInfo
 from pipecat.services.settings import (
     NOT_GIVEN,
     LLMSettings,
@@ -203,6 +203,10 @@ class GrokRealtimeLLMService(LLMService[GrokRealtimeLLMAdapter]):
     # Use the Grok-specific adapter
     adapter_class = GrokRealtimeLLMAdapter
 
+    # Realtime (speech-to-speech) service. Emits UserStarted/Stopped
+    # speaking frames from server-side VAD events.
+    _realtime_service_info = RealtimeServiceInfo(emits_user_turn_frames=True)
+
     def __init__(
         self,
         *,