diff --git a/litellm/llms/mistral/chat/transformation.py b/litellm/llms/mistral/chat/transformation.py
index 0d9577669a4..f6733d2b27c 100644
--- a/litellm/llms/mistral/chat/transformation.py
+++ b/litellm/llms/mistral/chat/transformation.py
@@ -253,6 +253,8 @@ class MistralConfig(OpenAIGPTConfig):
             m = strip_none_values_from_message(m)  # prevents 'extra_forbidden' error
             new_messages.append(m)
 
+        new_messages = self._strip_extra_fields(new_messages)
+
         if is_async:
             return super()._transform_messages(new_messages, model, True)
         else:
@@ -266,7 +268,7 @@ class MistralConfig(OpenAIGPTConfig):
         # and then apply Mistral-specific handling for files
         messages = await super()._transform_messages(messages, model, True)
         messages = self._handle_message_with_file(messages)
-        return messages
+        return self._strip_extra_fields(messages)
 
     def _transform_messages_sync(self, messages: list[AllMessageValues], model: str) -> list[AllMessageValues]:
         """Handle modification of messages for Mistral API in a sync context."""
@@ -275,6 +277,17 @@ class MistralConfig(OpenAIGPTConfig):
         # This is the sync version of the async method above
         messages = super()._transform_messages(messages, model, False)
         messages = self._handle_message_with_file(messages)
+        return self._strip_extra_fields(messages)
+
+    @staticmethod
+    def _strip_extra_fields(messages: list[AllMessageValues]) -> list[AllMessageValues]:
+        for m in messages:
+            if isinstance(m, dict) and m.get("role") == "assistant":
+                m.pop("metadata", None)
+                m.pop("provider_specific_fields", None)
+                m.pop("thinking_blocks", None)
+                m.pop("cache_control", None)
+                m.pop("reasoning_content", None)
         return messages
 
     def _handle_message_with_file(self, messages: list[AllMessageValues]) -> list[AllMessageValues]:
diff --git a/tests/test_litellm/llms/mistral/test_mistral_chat_transformation.py b/tests/test_litellm/llms/mistral/test_mistral_chat_transformation.py
index 15694d9f218..0cc92c36e47 100644
--- a/tests/test_litellm/llms/mistral/test_mistral_chat_transformation.py
+++ b/tests/test_litellm/llms/mistral/test_mistral_chat_transformation.py
@@ -245,6 +245,53 @@ class TestMistralReasoningSupport:
         assert result == messages
         assert len(result) == 1
 
+    def test_transform_messages_strips_extra_fields(self):
+        """GH#30882: extra fields like metadata should be stripped
+        from messages before sending to Mistral API."""
+        mistral_config = MistralConfig()
+        messages: List[AllMessageValues] = [
+            cast(
+                AllMessageValues,
+                {
+                    "role": "assistant",
+                    "content": "hello",
+                    "metadata": {
+                        "tool_outputs_trimmed": True,
+                        "trimmed_by": "async_context_compression",
+                    },
+                    "provider_specific_fields": {"foo": "bar"},
+                    "thinking_blocks": [],
+                    "cache_control": {"type": "ephemeral"},
+                    "reasoning_content": "some thinking",
+                },
+            )
+        ]
+        result = mistral_config._transform_messages(messages, "mistral/mistral-large-latest")
+        assert len(result) == 1
+        msg = cast(dict, result[0])
+        assert msg["role"] == "assistant"
+        assert msg["content"] == "hello"
+        assert "metadata" not in msg
+        assert "provider_specific_fields" not in msg
+        assert "thinking_blocks" not in msg
+        assert "cache_control" not in msg
+        assert "reasoning_content" not in msg
+
+    def test_user_message_extra_fields_are_preserved(self):
+        """GH#30882: user messages should not be stripped of extra fields."""
+        mistral_config = MistralConfig()
+        messages: List[AllMessageValues] = [
+            cast(
+                AllMessageValues,
+                {"role": "user", "content": "Question?", "reasoning_content": "noise"},
+            )
+        ]
+        result = mistral_config._transform_messages(messages, "mistral/mistral-large-latest")
+        assert len(result) == 1
+        msg = cast(dict, result[0])
+        assert msg["role"] == "user"
+        assert msg["reasoning_content"] == "noise"
+
     def test_transform_request_magistral_with_reasoning(self):
         """Test transform_request method for magistral model with reasoning."""
         mistral_config = MistralConfig()