From d6824173b10c383e4d69b9414ff86241998da67b Mon Sep 17 00:00:00 2001
From: mkzung <103102868+mkzung@users.noreply.github.com>
Date: Sun, 19 Jul 2026 18:46:35 +0500
Subject: [PATCH] fix(gigachat): don't claim stop support the provider lacks

get_supported_openai_params listed stop, but map_openai_params discarded it
with a comment saying GigaChat has no stop sequences. Listing it suppresses
the UnsupportedParamsError litellm raises for unsupported params, so the
sequences went missing with no error and generation ran on.

Dropping stop from the list restores the normal path: an error naming the
param, or a quiet drop under drop_params=True.
---
 litellm/llms/gigachat/chat/transformation.py |  9 +++---
 tests/llm_translation/test_gigachat.py       | 30 ++++++++++++++++++++
 2 files changed, 34 insertions(+), 5 deletions(-)

diff --git a/litellm/llms/gigachat/chat/transformation.py b/litellm/llms/gigachat/chat/transformation.py
index 4007588cfc5..02e052f724d 100644
--- a/litellm/llms/gigachat/chat/transformation.py
+++ b/litellm/llms/gigachat/chat/transformation.py
@@ -124,14 +124,16 @@ class GigaChatConfig(BaseConfig):
         return headers
 
     def get_supported_openai_params(self, model: str) -> list[str]:
-        """Return list of supported OpenAI parameters."""
+        """Return list of supported OpenAI parameters.
+
+        No stop: the GigaChat request body has no stop field.
+        """
         return [
             "stream",
             "temperature",
             "top_p",
             "max_tokens",
             "max_completion_tokens",
-            "stop",
             "tools",
             "tool_choice",
             "functions",
@@ -160,9 +162,6 @@ class GigaChatConfig(BaseConfig):
                 optional_params["top_p"] = value
             elif param in ("max_tokens", "max_completion_tokens"):
                 optional_params["max_tokens"] = value
-            elif param == "stop":
-                # GigaChat doesn't support stop sequences
-                pass
             elif param == "tools":
                 # Convert tools to functions format
                 optional_params["functions"] = self._convert_tools_to_functions(value)
diff --git a/tests/llm_translation/test_gigachat.py b/tests/llm_translation/test_gigachat.py
index 3c47f692ce0..2ebfacbb69e 100644
--- a/tests/llm_translation/test_gigachat.py
+++ b/tests/llm_translation/test_gigachat.py
@@ -359,6 +359,36 @@ class TestGigaChatSupportedParams:
         assert "response_format" in supported
         assert "stream" in supported
 
+    def test_stop_not_supported(self, config):
+        """GigaChat has no stop sequences, so it must not claim `stop`.
+
+        Claiming it suppresses the UnsupportedParamsError users rely on and the
+        sequences are dropped without any warning.
+        """
+        assert "stop" not in config.get_supported_openai_params("GigaChat")
+
+    def test_stop_raises_instead_of_being_dropped(self, config):
+        """Passing stop should surface an error, not vanish."""
+        import litellm
+        from litellm.utils import get_optional_params
+
+        with pytest.raises(litellm.UnsupportedParamsError):
+            get_optional_params(
+                model="GigaChat", custom_llm_provider="gigachat", stop=["END"]
+            )
+
+    def test_stop_still_droppable(self, config):
+        """With drop_params on, stop is dropped quietly - the documented escape."""
+        from litellm.utils import get_optional_params
+
+        params = get_optional_params(
+            model="GigaChat",
+            custom_llm_provider="gigachat",
+            stop=["END"],
+            drop_params=True,
+        )
+        assert "stop" not in params
+
 
 class TestGigaChatToolChoiceMapping:
     """Tests for tool_choice -> function_call mapping"""