fix(genai): propagate the stop instance attribute to the model

libs/genai/langchain_google_genai/chat_models.py

@@ -2694,7 +2694,7 @@ def _build_base_generation_config(
         config: dict[str, Any] = {
             "candidate_count": self.n,
             "temperature": kwargs.get("temperature", self.temperature),
-            "stop_sequences": stop,
+            "stop_sequences": stop if stop is not None else self.stop,
             "max_output_tokens": kwargs.get(
                 "max_output_tokens", self.max_output_tokens
             ),

libs/genai/tests/unit_tests/test_chat_models.py

@@ -4363,6 +4363,22 @@ def test_kwargs_override_stop() -> None:
     assert config.stop_sequences == ["me"]
 
 
+def test_instance_stop_is_propagated() -> None:
+    """Regression test for #1586.
+
+    The `stop` instance attribute must be propagated to the generation
+    config when no per-call `stop` is supplied.
+    """
+    llm = ChatGoogleGenerativeAI(
+        model=MODEL_NAME, google_api_key=SecretStr(FAKE_API_KEY), stop=["model"]
+    )
+
+    msg = HumanMessage(content="test")
+    request = llm._prepare_request([msg])
+    config = request["config"]
+    assert config.stop_sequences == ["model"]
+
+
 def test_kwargs_override_thinking_budget() -> None:
     """Test that thinking_budget can be overridden via kwargs."""
     llm = ChatGoogleGenerativeAI(