diff --git a/evalscope/evalscope/models/openai_compatible.py b/evalscope/evalscope/models/openai_compatible.py
index 6b50b52..2e84cbb 100644
--- a/evalscope/evalscope/models/openai_compatible.py
+++ b/evalscope/evalscope/models/openai_compatible.py
@@ -47,9 +47,8 @@ class OpenAICompatibleAPI(ModelAPI):
             config=config,
         )
 
-        # use service prefix to lookup api_key
-        self.api_key = api_key or os.environ.get('EVALSCOPE_API_KEY', None)
-        assert self.api_key, f'API key for {model_name} not found'
+        # use service prefix to lookup api_key; default to 'EMPTY' for local endpoints
+        self.api_key = api_key or os.environ.get('EVALSCOPE_API_KEY') or 'EMPTY'
 
         # use service prefix to lookup base_url
         self.base_url = base_url or os.environ.get('EVALSCOPE_BASE_URL', None)