fix(anthropic): default tool_choice to auto when only parallel_tool_calls is set

src/any_llm/providers/anthropic/utils.py

@@ -430,7 +430,7 @@ def _convert_tool_choice(params: CompletionParams) -> dict[str, Any]:
     parallel_tool_calls = params.parallel_tool_calls
     if parallel_tool_calls is None:
         parallel_tool_calls = True
-    tool_choice = params.tool_choice or "any"
+    tool_choice = params.tool_choice or "auto"
     if tool_choice == "required":
         tool_choice = "any"
     elif isinstance(tool_choice, dict):
@@ -480,7 +480,7 @@ def _convert_params(params: CompletionParams, **kwargs: Any) -> dict[str, Any]:
     if params.tools:
         params.tools = _convert_tool_spec(params.tools)
 
-    if params.tool_choice or params.parallel_tool_calls:
+    if params.tool_choice is not None or params.parallel_tool_calls is not None:
         params.tool_choice = _convert_tool_choice(params)
 
     if params.reasoning_effort is None or params.reasoning_effort == "none":

tests/unit/providers/test_anthropic_provider.py

@@ -309,6 +309,30 @@ async def test_completion_with_tool_choice_and_parallel_tool_calls(parallel_tool
         )
 
 
+@pytest.mark.parametrize("parallel_tool_calls", [True, False])
+@pytest.mark.asyncio
+async def test_completion_with_parallel_tool_calls_only(parallel_tool_calls: bool) -> None:
+    """Test that parallel_tool_calls without tool_choice maps to "auto" instead of forcing tool use."""
+    api_key = "test-api-key"
+    model = "model-id"
+    messages = [{"role": "user", "content": "Hello"}]
+
+    with mock_anthropic_provider() as mock_anthropic:
+        provider = AnthropicProvider(api_key=api_key)
+        await provider._acompletion(
+            CompletionParams(model_id=model, messages=messages, parallel_tool_calls=parallel_tool_calls),
+        )
+
+        expected_kwargs = {"tool_choice": {"type": "auto", "disable_parallel_tool_use": not parallel_tool_calls}}
+
+        mock_anthropic.return_value.messages.create.assert_called_once_with(
+            model=model,
+            messages=[{"role": "user", "content": "Hello"}],
+            **expected_kwargs,
+            max_tokens=DEFAULT_MAX_TOKENS,
+        )
+
+
 @pytest.mark.asyncio
 async def test_completion_inside_agent_loop(agent_loop_messages: list[dict[str, Any]]) -> None:
     api_key = "test-api-key"