fix(bedrock): omit empty additionalModelRequestFields and system from Converse API payload (#29565)

Amazon Nova Pro (and other strict Bedrock models) return 400 Malformed input
request when additionalModelRequestFields: {} or system: [] are present in the
payload. Both fields are optional in CommonRequestObject (total=False) and must
be omitted rather than sent as empty structures.

Co-authored-by: shin-berri <shin-laptop@berri.ai>
Co-authored-by: yuneng-jiang <yuneng@berri.ai>
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

litellm/llms/bedrock/chat/converse_transformation.py

@@ -1649,12 +1649,14 @@ class AmazonConverseConfig(BaseConfig):
                 bedrock_tool_config["toolChoice"] = tool_choice_values
 
         data: CommonRequestObject = {
-            "additionalModelRequestFields": additional_request_params,
-            "system": system_content_blocks,
             "inferenceConfig": self._transform_inference_params(
                 inference_params=inference_params
             ),
         }
+        if additional_request_params:
+            data["additionalModelRequestFields"] = additional_request_params
+        if system_content_blocks:
+            data["system"] = system_content_blocks
 
         # Handle all config blocks
         for config_name, config_class in self.get_config_blocks().items():

tests/llm_translation/test_bedrock_completion.py

@@ -3059,8 +3059,6 @@ async def test_bedrock_max_completion_tokens(model: str):
 
         assert request_body == {
             "messages": [{"role": "user", "content": [{"text": "Hello!"}]}],
-            "additionalModelRequestFields": {},
-            "system": [],
             "inferenceConfig": {"maxTokens": 10},
         }
 

tests/test_litellm/llms/bedrock/chat/test_converse_transformation.py

@@ -1467,11 +1467,10 @@ def test_transform_request_with_function_tool():
     )
 
     # Verify the structure
-    assert "additionalModelRequestFields" in request_data
-    additional_fields = request_data["additionalModelRequestFields"]
+    # Function tools are not computer use tools, so they don't get anthropic_beta —
+    # additionalModelRequestFields should be absent (not serialized as empty {})
+    assert "additionalModelRequestFields" not in request_data
 
-    # Function tools are not computer use tools, so they don't get anthropic_beta
-    # They are processed through the regular tool config
     assert "toolConfig" in request_data
     assert "tools" in request_data["toolConfig"]
     assert len(request_data["toolConfig"]["tools"]) == 1

tests/test_litellm/llms/bedrock/files/test_bedrock_files_transformation.py

@@ -128,6 +128,70 @@ class TestBedrockFilesTransformation:
         # Must have messages
         assert "messages" in model_input
 
+        # Nova Pro rejects empty additionalModelRequestFields / system — they must be absent
+        assert (
+            "additionalModelRequestFields" not in model_input
+        ), "Nova: empty additionalModelRequestFields must be omitted, not serialized as {}"
+        assert (
+            "system" not in model_input
+        ), "Nova: empty system must be omitted, not serialized as []"
+
+    def test_nova_batch_jsonl_omits_empty_converse_fields(self):
+        """
+        Regression test: Amazon Nova Pro returns 400 Malformed input request when
+        additionalModelRequestFields or system are present but empty in the Converse
+        API payload.  The proxy must strip these keys when they carry no data.
+        """
+        from litellm.llms.bedrock.files.transformation import BedrockFilesConfig
+
+        config = BedrockFilesConfig()
+
+        openai_jsonl_content = [
+            {
+                "custom_id": "req-0",
+                "method": "POST",
+                "url": "/v1/chat/completions",
+                "body": {
+                    "model": "us.amazon.nova-pro-v1:0",
+                    "messages": [
+                        {
+                            "role": "user",
+                            "content": "What is 1 + 1? Answer with just the number.",
+                        }
+                    ],
+                    "max_tokens": 16,
+                },
+            }
+        ]
+
+        result = config._transform_openai_jsonl_content_to_bedrock_jsonl_content(
+            openai_jsonl_content
+        )
+
+        assert len(result) == 1
+        model_input = result[0]["modelInput"]
+
+        assert (
+            "additionalModelRequestFields" not in model_input
+            or model_input["additionalModelRequestFields"]
+        ), "additionalModelRequestFields must be absent or non-empty — Nova rejects {}"
+        assert (
+            "system" not in model_input or model_input["system"]
+        ), "system must be absent or non-empty — Nova rejects []"
+
+        # Validate the exact shape AWS accepts
+        assert model_input == {
+            "messages": [
+                {
+                    "role": "user",
+                    "content": [
+                        {"text": "What is 1 + 1? Answer with just the number."}
+                    ],
+                }
+            ],
+            "inferenceConfig": {"maxTokens": 16},
+        }
+
     def test_nova_image_content_uses_converse_image_blocks(self):
         """
         Test that image_url content blocks are converted to Bedrock Converse