Fix converse handling for parallel_tool_calls

litellm/llms/bedrock/chat/converse_transformation.py

@@ -511,6 +511,7 @@ class AmazonConverseConfig(BaseConfig):
             "response_format",
             "requestMetadata",
             "service_tier",
+            "parallel_tool_calls",
         ]
 
         if (
@@ -913,6 +914,13 @@ class AmazonConverseConfig(BaseConfig):
                 )
                 if _tool_choice_value is not None:
                     optional_params["tool_choice"] = _tool_choice_value
+            if param == "parallel_tool_calls":
+                disable_parallel = not value
+                optional_params["_parallel_tool_use_config"] = {
+                    "tool_choice": {
+                        "disable_parallel_tool_use": disable_parallel
+                    }
+                }
             if param == "thinking":
                 optional_params["thinking"] = value
             elif param == "reasoning_effort" and isinstance(value, str):
@@ -1207,6 +1215,17 @@ class AmazonConverseConfig(BaseConfig):
             k: v for k, v in inference_params.items() if k in total_supported_params
         }
 
+        # Handle parallel_tool_calls configuration
+        parallel_tool_use_config = additional_request_params.pop("_parallel_tool_use_config", None)
+        if parallel_tool_use_config is not None and is_claude_4_5_on_bedrock(model):
+            for key, value in parallel_tool_use_config.items():
+                if key in additional_request_params and isinstance(additional_request_params[key], dict) and isinstance(value, dict):
+                    additional_request_params[key].update(value)
+                else:
+                    additional_request_params[key] = value
+
+        additional_request_params.pop("parallel_tool_calls", None)
+
         # Only set the topK value in for models that support it
         additional_request_params.update(
             self._handle_top_k_value(model, inference_params)

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

@@ -2616,11 +2616,11 @@ def test_empty_assistant_message_handling():
     empty or whitespace-only content with a placeholder to prevent AWS Bedrock
     Converse API 400 Bad Request errors.
     """
+    # Import the litellm module that factory.py uses to ensure we patch the correct reference
+    import litellm.litellm_core_utils.prompt_templates.factory as factory_module
     from litellm.litellm_core_utils.prompt_templates.factory import (
         _bedrock_converse_messages_pt,
     )
-    # Import the litellm module that factory.py uses to ensure we patch the correct reference
-    import litellm.litellm_core_utils.prompt_templates.factory as factory_module
 
     # Test case 1: Empty string content - test with modify_params=True to prevent merging
     messages = [
@@ -3135,7 +3135,12 @@ def test_native_structured_output_no_fake_stream():
 
 def test_transform_request_with_output_config():
     """Test that outputConfig flows through _transform_request_helper into the final request."""
-    from litellm.types.llms.bedrock import OutputConfigBlock, OutputFormat, OutputFormatStructure, JsonSchemaDefinition
+    from litellm.types.llms.bedrock import (
+        JsonSchemaDefinition,
+        OutputConfigBlock,
+        OutputFormat,
+        OutputFormatStructure,
+    )
 
     config = AmazonConverseConfig()
 
@@ -3377,6 +3382,80 @@ def test_output_config_applies_additional_properties():
 
 
 
+_TOOL_PARAM = [
+    {
+        "type": "function",
+        "function": {
+            "name": "get_weather",
+            "description": "Get the weather",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "location": {
+                        "type": "string",
+                        "description": "The location to get weather for",
+                    }
+                },
+                "required": ["location"],
+            },
+        },
+    }
+]
+
+
+def test_parallel_tool_calls_newer_model_adds_disable_flag():
+    """Newer Claude models (4.5+) should get disable_parallel_tool_use in additionalModelRequestFields."""
+    config = AmazonConverseConfig()
+    model = "anthropic.claude-sonnet-4-5-20250929-v1:0"
+    messages = [{"role": "user", "content": "What's the weather in SF and NYC?"}]
+
+    optional_params = config.map_openai_params(
+        non_default_params={"parallel_tool_calls": False, "tools": _TOOL_PARAM},
+        optional_params={},
+        model=model,
+        drop_params=False,
+    )
+
+    request_data = config.transform_request(
+        model=model,
+        messages=messages,
+        optional_params=optional_params,
+        litellm_params={},
+        headers={},
+    )
+
+    assert "additionalModelRequestFields" in request_data
+    assert "tool_choice" in request_data["additionalModelRequestFields"]
+    assert request_data["additionalModelRequestFields"]["tool_choice"]["disable_parallel_tool_use"] is True
+    assert "parallel_tool_calls" not in request_data["additionalModelRequestFields"]
+
+
+def test_parallel_tool_calls_older_model_drops_disable_flag():
+    """Older Claude models (pre-4.5) must NOT receive disable_parallel_tool_use — Bedrock rejects it."""
+    config = AmazonConverseConfig()
+    model = "anthropic.claude-3-5-sonnet-20241022-v2:0"
+    messages = [{"role": "user", "content": "What's the weather in SF and NYC?"}]
+
+    optional_params = config.map_openai_params(
+        non_default_params={"parallel_tool_calls": False, "tools": _TOOL_PARAM},
+        optional_params={},
+        model=model,
+        drop_params=False,
+    )
+
+    request_data = config.transform_request(
+        model=model,
+        messages=messages,
+        optional_params=optional_params,
+        litellm_params={},
+        headers={},
+    )
+
+    additional = request_data.get("additionalModelRequestFields", {})
+    assert "tool_choice" not in additional
+    assert "parallel_tool_calls" not in additional
+
+
 class TestBedrockMinThinkingBudgetTokens:
     """Test that thinking.budget_tokens is clamped to the Bedrock minimum (1024)."""