Add Grok-4 to free models, update Mistral to mistral-medium-2505

app.py

@@ -25,9 +25,10 @@ FREE_MODEL_CHOICES = [
     "meta-llama/Llama-4.1-8B-Instruct:novita",
     "gemini-2.5-flash",
     "gpt-4o",
-    "mistral-medium-latest",
+    "mistral-medium-2505",
     "claude-3-haiku-20240307",
     "sonar",
+    "grok-4-fast-non-reasoning",
 ]
 
 # Paid models (user provides their own API key)
@@ -135,6 +136,10 @@ def classify_data(spreadsheet_file, spreadsheet_column,
             actual_api_key = os.environ.get("PERPLEXITY_API_KEY", "")
             if not actual_api_key:
                 return None, None, "**Error:** Perplexity API key not configured in Space secrets"
+        elif "grok" in model.lower():
+            actual_api_key = os.environ.get("XAI_API_KEY", "")
+            if not actual_api_key:
+                return None, None, "**Error:** xAI API key not configured in Space secrets"
         else:
             actual_api_key = os.environ.get("HF_API_KEY", "")
     else: