diff --git a/backend/src/plugins/llm_analysis/service.py b/backend/src/plugins/llm_analysis/service.py
index 5c4ca40a..70bebe54 100644
--- a/backend/src/plugins/llm_analysis/service.py
+++ b/backend/src/plugins/llm_analysis/service.py
@@ -935,18 +935,15 @@ class LLMClient:
     # @PRE Client initialized with base_url and default_model.
     # @POST Returns False for known-incompatible combinations to avoid avoidable 400 errors.
     def _supports_json_response_format(self) -> bool:
-        base = (self.base_url or "").lower()
         model = (self.default_model or "").lower()
 
-        # OpenRouter routes to many upstream providers; some models reject json_object mode.
-        if "openrouter.ai" in base:
-            incompatible_tokens = (
-                "stepfun/",
-                "step-",
-                ":free",
-            )
-            if any(token in model for token in incompatible_tokens):
-                return False
+        # Free-tier models from ANY gateway often reject json_object mode
+        # (Nvidia NeMo free via OpenRouter or Kilo, stepfun free, etc.)
+        if ":free" in model:
+            return False
+        # stepfun models (even non-free) don't support json_object mode
+        if "stepfun/" in model or model.startswith("step-"):
+            return False
         return True
     # endregion LLMClient._supports_json_response_format