feat(tts): add websocket transport option for xAI TTS (#548)

* feat(tts): add websocket transport option for xAI TTS

xAI's pipecat service ships two implementations: XAIHttpTTSService
(batch REST, used by the existing xAI integration) and XAITTSService
(realtime WebSocket streaming). This adds a transport field on
XAITTSConfiguration ("http", default, unchanged behavior | "websocket")
and wires the latter into create_tts_service(), so live voice calls can
opt into lower time-to-first-byte streaming instead of request/response.

Originally built and battle-tested independently against v1.41.0 in a
production deployment (7 live Telnyx calls, 2026-07-15) before this PR
existed; ported onto current main and given a config toggle instead of
a second provider entry so it composes with the existing xAI HTTP path
rather than duplicating it.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* refactor(tts): use websocket-only xAI TTS, drop the transport toggle

---------

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
Co-authored-by: Sabiha Khan <sabihak89@gmail.com>

api/services/configuration/registry.py

@@ -1332,7 +1332,6 @@ class XAITTSConfiguration(BaseServiceConfiguration):
         description="BCP-47 language code for synthesis (e.g. 'en', 'fr', 'de'), or 'auto' for automatic language detection.",
         json_schema_extra={"allow_custom_input": True},
     )
-
     @computed_field
     @property
     def model(self) -> str:

api/services/pipecat/service_factory.py

@@ -86,7 +86,7 @@ from pipecat.services.speechmatics.stt import (
     SpeechmaticsSTTService,
     SpeechmaticsSTTSettings,
 )
-from pipecat.services.xai.tts import XAIHttpTTSService, XAITTSSettings
+from pipecat.services.xai.tts import XAITTSService, XAIWebsocketTTSSettings
 from pipecat.transcriptions.language import Language
 from pipecat.utils.text.xml_function_tag_filter import XMLFunctionTagFilter
 
@@ -817,11 +817,9 @@ def create_tts_service(
                 pipecat_language = Language(language_code)
             except ValueError:
                 pipecat_language = Language.EN
-        return XAIHttpTTSService(
+        return XAITTSService(
             api_key=user_config.tts.api_key,
-            sample_rate=audio_config.transport_out_sample_rate,
-            encoding="pcm",
-            settings=XAITTSSettings(
+            settings=XAIWebsocketTTSSettings(
                 voice=voice,
                 language=pipecat_language,
             ),

api/tests/test_xai_tts_service_factory.py

@@ -24,10 +24,7 @@ def test_xai_tts_configuration_defaults():
     assert XAI_TTS_VOICES == ["eve", "ara", "leo", "rex", "sal"]
 
 
-@pytest.mark.parametrize("transport_out_sample_rate", [8000, 16000])
-def test_create_xai_tts_service_uses_pipeline_compatible_audio_format(
-    transport_out_sample_rate,
-):
+def test_create_xai_tts_service_uses_websocket_streaming():
     user_config = SimpleNamespace(
         tts=SimpleNamespace(
             provider=ServiceProviders.XAI.value,
@@ -38,20 +35,18 @@ def test_create_xai_tts_service_uses_pipeline_compatible_audio_format(
         )
     )
     audio_config = SimpleNamespace(
-        transport_out_sample_rate=transport_out_sample_rate,
+        transport_out_sample_rate=24000,
         transport_in_sample_rate=16000,
     )
 
-    with patch(
-        "api.services.pipecat.service_factory.XAIHttpTTSService"
-    ) as mock_service:
+    with patch("api.services.pipecat.service_factory.XAITTSService") as mock_service:
         create_tts_service(user_config, audio_config)
 
     assert mock_service.call_count == 1
     kwargs = mock_service.call_args.kwargs
     assert kwargs["api_key"] == "test-key"
-    assert kwargs["sample_rate"] == transport_out_sample_rate
-    assert kwargs["encoding"] == "pcm"
+    # Sample rate is resolved from the pipeline StartFrame, like other providers.
+    assert "sample_rate" not in kwargs
     assert kwargs["settings"].voice == "rex"
     assert kwargs["settings"].language == Language.EN
 
@@ -71,9 +66,7 @@ def test_create_xai_tts_service_converts_language():
         transport_in_sample_rate=16000,
     )
 
-    with patch(
-        "api.services.pipecat.service_factory.XAIHttpTTSService"
-    ) as mock_service:
+    with patch("api.services.pipecat.service_factory.XAITTSService") as mock_service:
         create_tts_service(user_config, audio_config)
 
     kwargs = mock_service.call_args.kwargs
@@ -95,9 +88,7 @@ def test_create_xai_tts_service_falls_back_to_english_for_unknown_language():
         transport_in_sample_rate=16000,
     )
 
-    with patch(
-        "api.services.pipecat.service_factory.XAIHttpTTSService"
-    ) as mock_service:
+    with patch("api.services.pipecat.service_factory.XAITTSService") as mock_service:
         create_tts_service(user_config, audio_config)
 
     kwargs = mock_service.call_args.kwargs
@@ -119,9 +110,7 @@ def test_create_xai_tts_service_preserves_auto_language():
         transport_in_sample_rate=16000,
     )
 
-    with patch(
-        "api.services.pipecat.service_factory.XAIHttpTTSService"
-    ) as mock_service:
+    with patch("api.services.pipecat.service_factory.XAITTSService") as mock_service:
         create_tts_service(user_config, audio_config)
 
     kwargs = mock_service.call_args.kwargs

ui/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "ui",
-  "version": "1.41.0",
+  "version": "1.42.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "ui",
-      "version": "1.41.0",
+      "version": "1.42.0",
       "dependencies": {
         "@calcom/embed-react": "^1.5.3",
         "@dagrejs/dagre": "^1.1.4",