Add xAI streaming STT service

New `XAISTTService` wraps xAI's real-time speech-to-text WebSocket
(`wss://api.x.ai/v1/stt`). It extends `WebsocketSTTService`, authenticates
with the `XAI_API_KEY` as a Bearer token on the WS handshake, and streams
raw audio (PCM/mu-law/A-law) with configurable interim results, endpointing,
language, multichannel, and diarization settings.

- `src/pipecat/services/xai/stt.py`: new service, settings dataclass, and
  `language_to_xai_stt_language` helper.
- `src/pipecat/services/stt_latency.py`: `XAI_TTFS_P99` default.
- `pyproject.toml` / `uv.lock`: `xai` extra now pulls in `websockets-base`.
- `README.md`: link to xAI STT in the services table.
- `examples/voice/voice-xai.py`: swap DeepgramSTTService for XAISTTService so
  the xAI voice example is fully xAI.
- `examples/transcription/transcription-xai.py`: new transcription-only
  example using the new service.

examples/transcription/transcription-xai.py

@@ -0,0 +1,89 @@
+#
+# Copyright (c) 2024-2026, Daily
+#
+# SPDX-License-Identifier: BSD 2-Clause License
+#
+
+import os
+
+from dotenv import load_dotenv
+from loguru import logger
+
+from pipecat.audio.vad.silero import SileroVADAnalyzer
+from pipecat.frames.frames import Frame, TranscriptionFrame
+from pipecat.pipeline.pipeline import Pipeline
+from pipecat.pipeline.runner import PipelineRunner
+from pipecat.pipeline.task import PipelineTask
+from pipecat.processors.audio.vad_processor import VADProcessor
+from pipecat.processors.frame_processor import FrameDirection, FrameProcessor
+from pipecat.runner.types import RunnerArguments
+from pipecat.runner.utils import create_transport
+from pipecat.services.xai.stt import XAISTTService
+from pipecat.transports.base_transport import BaseTransport, TransportParams
+from pipecat.transports.daily.transport import DailyParams
+from pipecat.transports.websocket.fastapi import FastAPIWebsocketParams
+
+load_dotenv(override=True)
+
+
+class TranscriptionLogger(FrameProcessor):
+    async def process_frame(self, frame: Frame, direction: FrameDirection):
+        await super().process_frame(frame, direction)
+
+        if isinstance(frame, TranscriptionFrame):
+            print(f"Transcription: {frame.text}")
+
+        # Push all frames through
+        await self.push_frame(frame, direction)
+
+
+transport_params = {
+    "daily": lambda: DailyParams(
+        audio_in_enabled=True,
+    ),
+    "twilio": lambda: FastAPIWebsocketParams(
+        audio_in_enabled=True,
+    ),
+    "webrtc": lambda: TransportParams(
+        audio_in_enabled=True,
+    ),
+}
+
+
+async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
+    logger.info(f"Starting bot")
+
+    stt = XAISTTService(
+        api_key=os.getenv("XAI_API_KEY"),
+    )
+
+    tl = TranscriptionLogger()
+    vad_processor = VADProcessor(vad_analyzer=SileroVADAnalyzer())
+
+    pipeline = Pipeline([transport.input(), vad_processor, stt, tl])
+
+    task = PipelineTask(
+        pipeline,
+        idle_timeout_secs=runner_args.pipeline_idle_timeout_secs,
+    )
+
+    @transport.event_handler("on_client_disconnected")
+    async def on_client_disconnected(transport, client):
+        logger.info(f"Client disconnected")
+        await task.cancel()
+
+    runner = PipelineRunner(handle_sigint=runner_args.handle_sigint)
+
+    await runner.run(task)
+
+
+async def bot(runner_args: RunnerArguments):
+    """Main bot entry point compatible with Pipecat Cloud."""
+    transport = await create_transport(runner_args, transport_params)
+    await run_bot(transport, runner_args)
+
+
+if __name__ == "__main__":
+    from pipecat.runner.run import main
+
+    main()

examples/voice/voice-xai.py

@@ -22,8 +22,8 @@ from pipecat.processors.aggregators.llm_response_universal import (
 )
 from pipecat.runner.types import RunnerArguments
 from pipecat.runner.utils import create_transport
-from pipecat.services.deepgram.stt import DeepgramSTTService
 from pipecat.services.xai.llm import GrokLLMService
+from pipecat.services.xai.stt import XAISTTService
 from pipecat.services.xai.tts import XAIHttpTTSService
 from pipecat.transports.base_transport import BaseTransport, TransportParams
 from pipecat.transports.daily.transport import DailyParams
@@ -53,7 +53,7 @@ async def run_bot(transport: BaseTransport, runner_args: RunnerArguments):
     logger.info(f"Starting bot")
 
     async with aiohttp.ClientSession() as session:
-        stt = DeepgramSTTService(api_key=os.getenv("DEEPGRAM_API_KEY"))
+        stt = XAISTTService(api_key=os.getenv("XAI_API_KEY"))
 
         tts = XAIHttpTTSService(
             api_key=os.getenv("XAI_API_KEY"),