Set Explainer model in Environment variables

app.py

@@ -27,6 +27,7 @@ OPENROUTER_API_KEY = os.environ.get("OPENROUTER_API_KEY")
 if not OPENROUTER_API_KEY:
     raise RuntimeError("OPENROUTER_API_KEY environment variable not set!")
 
+EXPLAIN_MODEL = os.environ.get("EXPLAIN_MODEL")
 # ---------------------------------------------------------------------------
 # Global rate limiter for OpenRouter calls
 #
@@ -95,7 +96,7 @@ def call_openrouter(payload: dict, headers: dict, timeout: int = 20):
 class ExplainRequest(BaseModel):
     message: str
     label: str = None  # Optional, for explanations
-    model_id: str = "openai/gpt-oss-120b:free"  # Default model, can be overridden
+    model_id: str = EXPLAIN_MODEL  # Default model, can be overridden
 
 @app.get("/")
 def root():