From 7684a94c33dc3e26af70231fcffd4e205af16a94 Mon Sep 17 00:00:00 2001
From: Mark Backman <mark@daily.co>
Date: Wed, 4 Feb 2026 19:15:57 -0500
Subject: [PATCH] AssemblyAISTTService: Disable turn detection when setting
 vad_force_turn_endpoint to True

---
 changelog/3644.changed.md              |  1 +
 src/pipecat/services/assemblyai/stt.py | 56 +++++++++++++++++++++++++-
 2 files changed, 56 insertions(+), 1 deletion(-)
 create mode 100644 changelog/3644.changed.md

diff --git a/changelog/3644.changed.md b/changelog/3644.changed.md
new file mode 100644
index 000000000..8b1511b9f
--- /dev/null
+++ b/changelog/3644.changed.md
@@ -0,0 +1 @@
+- `AssemblyAISTTService` now automatically configures optimal settings for manual turn detection when `vad_force_turn_endpoint=True`. This sets `end_of_turn_confidence_threshold=1.0` and `max_turn_silence=2000` by default, which disables model-based turn detection and reduces latency by relying on external VAD for turn endpoints. Warnings are logged if conflicting settings are detected.
diff --git a/src/pipecat/services/assemblyai/stt.py b/src/pipecat/services/assemblyai/stt.py
index 94fad23b7..41a0ae2a0 100644
--- a/src/pipecat/services/assemblyai/stt.py
+++ b/src/pipecat/services/assemblyai/stt.py
@@ -78,11 +78,19 @@ class AssemblyAISTTService(WebsocketSTTService):
             language: Language code for transcription. Defaults to English (Language.EN).
             api_endpoint_base_url: WebSocket endpoint URL. Defaults to AssemblyAI's streaming endpoint.
             connection_params: Connection configuration parameters. Defaults to AssemblyAIConnectionParams().
-            vad_force_turn_endpoint: Whether to force turn endpoint on VAD stop. Defaults to True.
+            vad_force_turn_endpoint: Whether to force turn endpoint on VAD stop. When True,
+                disables AssemblyAI's model-based turn detection and relies on external VAD
+                to trigger turn endpoints. Automatically sets end_of_turn_confidence_threshold=1.0
+                and max_turn_silence=2000 unless explicitly overridden. Defaults to True.
             ttfs_p99_latency: P99 latency from speech end to final transcript in seconds.
                 Override for your deployment. See https://github.com/pipecat-ai/stt-benchmark
             **kwargs: Additional arguments passed to parent STTService class.
         """
+        # When vad_force_turn_endpoint is enabled, configure connection params for manual
+        # turn detection mode (disable model-based turn detection)
+        if vad_force_turn_endpoint:
+            connection_params = self._configure_manual_turn_mode(connection_params)
+
         super().__init__(
             sample_rate=connection_params.sample_rate, ttfs_p99_latency=ttfs_p99_latency, **kwargs
         )
@@ -103,6 +111,52 @@ class AssemblyAISTTService(WebsocketSTTService):
         self._chunk_size_ms = 50
         self._chunk_size_bytes = 0
 
+    def _configure_manual_turn_mode(
+        self, connection_params: AssemblyAIConnectionParams
+    ) -> AssemblyAIConnectionParams:
+        """Configure connection params for manual turn detection mode.
+
+        When vad_force_turn_endpoint is enabled, we want to disable AssemblyAI's
+        model-based turn detection and rely on external VAD. This requires:
+        - end_of_turn_confidence_threshold=1.0 (disable semantic turn detection)
+        - max_turn_silence=2000 (high value since VAD handles turn endings)
+
+        Args:
+            connection_params: The user-provided connection parameters.
+
+        Returns:
+            Updated connection parameters configured for manual turn mode.
+        """
+        updates = {}
+
+        # Check end_of_turn_confidence_threshold
+        if connection_params.end_of_turn_confidence_threshold is None:
+            updates["end_of_turn_confidence_threshold"] = 1.0
+        elif connection_params.end_of_turn_confidence_threshold != 1.0:
+            logger.warning(
+                f"vad_force_turn_endpoint is enabled but end_of_turn_confidence_threshold "
+                f"is set to {connection_params.end_of_turn_confidence_threshold}. "
+                f"For manual turn detection mode, this should be 1.0 to disable "
+                f"model-based turn detection. The current value will be used."
+            )
+
+        # Check max_turn_silence
+        if connection_params.max_turn_silence is None:
+            updates["max_turn_silence"] = 2000
+        elif connection_params.max_turn_silence < 1000:
+            logger.warning(
+                f"vad_force_turn_endpoint is enabled but max_turn_silence is set to "
+                f"{connection_params.max_turn_silence}ms. With manual turn detection, "
+                f"a higher value (e.g., 2000ms) is recommended to avoid premature "
+                f"turn endings. The current value will be used."
+            )
+
+        # Apply updates if any
+        if updates:
+            connection_params = connection_params.model_copy(update=updates)
+
+        return connection_params
+
     def can_generate_metrics(self) -> bool:
         """Check if the service can generate metrics.