diff --git a/strix/config/models.py b/strix/config/models.py
index 7f676b2a..d8444ee1 100644
--- a/strix/config/models.py
+++ b/strix/config/models.py
@@ -808,13 +808,11 @@ def uses_chat_completions_tool_schema(model_name: str, settings: Settings) -> bo
     """Return whether the resolved SDK route can only receive JSON function tools."""
     if codex.subscription_model(model_name):
         return False
-    if settings.llm.api_type == "chat_completions":
-        return True
-    if settings.llm.api_type == "responses":
-        return False
     model = model_name.strip().lower()
     if "/" in model and not model.startswith("openai/"):
         return True
+    if settings.llm.api_type is not None:
+        return settings.llm.api_type == "chat_completions"
     if settings.llm.api_base:
         return True
     return not model_supports_reasoning(model_name)
diff --git a/tests/test_models.py b/tests/test_models.py
index 7b5556cc..7078ca98 100644
--- a/tests/test_models.py
+++ b/tests/test_models.py
@@ -184,6 +184,8 @@ def test_api_type_override_settings(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.setenv("STRIX_LLM", "openai/gpt-4")
     monkeypatch.setenv("STRIX_API_TYPE", "responses")
     assert uses_chat_completions_tool_schema("openai/gpt-4", Settings()) is False
+    monkeypatch.setenv("STRIX_LLM", "anthropic/claude-sonnet-4-5")
+    assert uses_chat_completions_tool_schema("anthropic/claude-sonnet-4-5", Settings()) is True
 
 
 @pytest.mark.parametrize(