diff --git a/litellm/llms/anthropic/messages/native/transformation.py b/litellm/llms/anthropic/messages/native/transformation.py
index 29b2beb1d7c..3a8cb8b5b4c 100644
--- a/litellm/llms/anthropic/messages/native/transformation.py
+++ b/litellm/llms/anthropic/messages/native/transformation.py
@@ -231,14 +231,13 @@ class AnthropicMessagesConfig(BaseAnthropicMessagesConfig):
             return system_param
 
     def _strip_beta_gated_system_turns(
-        self, messages: Sequence[object], model: str, drop_params: object
-    ) -> tuple[Mapping[str, object], ...]:
-        validated: Final = _MESSAGE_MAPPINGS.validate_python(messages)
+        self, messages: Sequence[Mapping[str, object]], model: str, drop_params: object
+    ) -> Sequence[Mapping[str, object]]:
         if not has_beta_headers_config(self._resolved_provider):
-            return validated
-        gated: Final = strip_beta_gated_system_messages(validated, frozenset(), drop_params=drop_params)
+            return messages
+        gated: Final = strip_beta_gated_system_messages(messages, frozenset(), drop_params=drop_params)
         log_beta_gated_strips(gated.stripped, model=model, provider=self._resolved_provider)
-        return _MESSAGE_MAPPINGS.validate_python(gated.messages) if gated.stripped else validated
+        return _MESSAGE_MAPPINGS.validate_python(gated.messages) if gated.stripped else messages
 
     def _normalize_system_role_messages(
         self, anthropic_messages_request: dict, model: str, drop_params: object
diff --git a/tests/unit/llms/vertex_ai/vertex_ai_partner_models/anthropic/test_vertex_ai_partner_models_anthropic_messages_config.py b/tests/unit/llms/vertex_ai/vertex_ai_partner_models/anthropic/test_vertex_ai_partner_models_anthropic_messages_config.py
index 47c87c7e850..48611f5715d 100644
--- a/tests/unit/llms/vertex_ai/vertex_ai_partner_models/anthropic/test_vertex_ai_partner_models_anthropic_messages_config.py
+++ b/tests/unit/llms/vertex_ai/vertex_ai_partner_models/anthropic/test_vertex_ai_partner_models_anthropic_messages_config.py
@@ -851,6 +851,20 @@ class TestVertexAnthropicMidConversationSystem:
             {"type": "text", "text": "Cite sources."},
         ]
 
+    @pytest.mark.parametrize("drop_params", (False, True))
+    def test_unsupported_model_sends_a_non_object_message_on_for_the_provider_to_reject(
+        self, local_model_cost_map, local_beta_headers_config, drop_params
+    ):
+        messages: Final = [{"role": "user", "content": "hi"}, "oops"]
+        result: Final = VertexAIPartnerModelsAnthropicMessagesConfig().transform_anthropic_messages_request(
+            model="claude-sonnet-4-6",
+            messages=list(messages),
+            anthropic_messages_optional_request_params={"max_tokens": 64},
+            litellm_params=GenericLiteLLMParams(drop_params=drop_params),
+            headers={},
+        )
+        assert result["messages"] == messages
+
     def test_unsupported_model_converts_mid_conversation_system_in_place(self, local_model_cost_map):
         messages = [
             {"role": "user", "content": "read the file"},