feat(stt): add speaker diarization support to STT interface and proxy

livekit-agents/livekit/agents/inference/stt.py

@@ -69,6 +69,7 @@ class DeepgramOptions(TypedDict, total=False):
     numerals: bool
     mip_opt_out: bool
     vad_events: bool  # default: False
+    diarize: bool  # default: False - enables speaker diarization
 
 
 class AssemblyaiOptions(TypedDict, total=False):
@@ -78,6 +79,7 @@ class AssemblyaiOptions(TypedDict, total=False):
     max_turn_silence: int  # default: not specified
     keyterms_prompt: list[str]  # default: not specified
     prompt: str  # default: not specified (u3-rt-pro only, mutually exclusive with keyterms_prompt)
+    speaker_labels: bool  # default: False - enables speaker diarization
 
 
 class ElevenlabsOptions(TypedDict, total=False):
@@ -286,10 +288,19 @@ def __init__(
                 a list of FallbackModel instances.
             conn_options (APIConnectOptions, optional): Connection options for request attempts.
         """
+        # Check extra_kwargs for diarization parameters across different providers
+        # Deepgram uses "diarize", AssemblyAI uses "speaker_labels"
+        diarization_enabled = False
+        if is_given(extra_kwargs):
+            diarization_enabled = bool(
+                extra_kwargs.get("diarize") or extra_kwargs.get("speaker_labels")
+            )
+
         super().__init__(
             capabilities=stt.STTCapabilities(
                 streaming=True,
                 interim_results=True,
+                diarization=diarization_enabled,
                 aligned_transcript="word",
                 offline_recognize=False,
             ),
@@ -410,6 +421,12 @@ def update_options(
             self._opts.language = LanguageCode(language)
         if is_given(extra):
             self._opts.extra_kwargs.update(extra)
+            # Update diarization capability based on extra_kwargs
+            diarization_enabled = bool(
+                self._opts.extra_kwargs.get("diarize")
+                or self._opts.extra_kwargs.get("speaker_labels")
+            )
+            self._capabilities = replace(self._capabilities, diarization=diarization_enabled)
 
         for stream in self._streams:
             stream.update_options(model=model, language=language, extra=extra)
@@ -651,13 +668,15 @@ def _process_transcript(self, data: dict, is_final: bool) -> None:
             end_time=self.start_time_offset + data.get("start", 0) + data.get("duration", 0),
             confidence=data.get("confidence", 1.0),
             text=text,
+            speaker_id=data.get("speaker_id"),
             words=[
                 TimedString(
                     text=word.get("word", ""),
                     start_time=word.get("start", 0) + self.start_time_offset,
                     end_time=word.get("end", 0) + self.start_time_offset,
                     start_time_offset=self.start_time_offset,
                     confidence=word.get("confidence", 0.0),
+                    speaker_id=word.get("speaker_id"),
                 )
                 for word in words
             ],

livekit-agents/livekit/agents/types.py

@@ -143,6 +143,7 @@ class TimedString(str):
     confidence: NotGivenOr[float]
     start_time_offset: NotGivenOr[float]
     # offset relative to the start of the audio input stream or session in seconds, used in STT plugins
+    speaker_id: str | None
 
     def __new__(
         cls,
@@ -151,10 +152,12 @@ def __new__(
         end_time: NotGivenOr[float] = NOT_GIVEN,
         confidence: NotGivenOr[float] = NOT_GIVEN,
         start_time_offset: NotGivenOr[float] = NOT_GIVEN,
+        speaker_id: str | None = None,
     ) -> "TimedString":
         obj = super().__new__(cls, text)
         obj.start_time = start_time
         obj.end_time = end_time
         obj.confidence = confidence
         obj.start_time_offset = start_time_offset
+        obj.speaker_id = speaker_id
         return obj

tests/test_inference_stt_fallback.py

@@ -257,3 +257,31 @@ def test_connect_options_full_custom(self):
         assert stt._opts.conn_options.timeout == 60.0
         assert stt._opts.conn_options.max_retry == 10
         assert stt._opts.conn_options.retry_interval == 2.0
+
+
+class TestSTTDiarizationCapabilities:
+    """Tests for STT diarization capability detection from extra_kwargs."""
+
+    def test_no_diarization_by_default(self):
+        """Without diarization params, capabilities.diarization is False."""
+        stt = _make_stt()
+        assert stt.capabilities.diarization is False
+
+    def test_diarization_enabled_with_deepgram_diarize(self):
+        """Deepgram's 'diarize' param enables diarization capability."""
+        stt = _make_stt(extra_kwargs={"diarize": True})
+        assert stt.capabilities.diarization is True
+
+    def test_diarization_enabled_with_assemblyai_speaker_labels(self):
+        """AssemblyAI's 'speaker_labels' param enables diarization capability."""
+        stt = _make_stt(model="assemblyai/universal-streaming", extra_kwargs={"speaker_labels": True})
+        assert stt.capabilities.diarization is True
+
+    def test_update_options_toggles_diarization(self):
+        """update_options can enable and disable diarization capability."""
+        stt = _make_stt()
+        assert stt.capabilities.diarization is False
+        stt.update_options(extra={"diarize": True})
+        assert stt.capabilities.diarization is True
+        stt.update_options(extra={"diarize": False})
+        assert stt.capabilities.diarization is False