fix(vertex_ai): auto-resolve vertex_location from supported_regions

- Add call to get_vertex_region() in partner models to auto-detect region
- Improve get_vertex_region() to read supported_regions from model_cost
- User-specified vertex_location still takes priority

litellm/llms/vertex_ai/vertex_ai_partner_models/main.py

@@ -161,6 +161,11 @@ class VertexAIPartnerModels(VertexBase):
             else:
                 raise ValueError(f"Unknown partner model: {model}")
 
+            # Resolve vertex_location based on model's supported_regions
+            vertex_location = self.get_vertex_region(
+                vertex_region=vertex_location, model=model
+            )
+
             api_base = self.get_complete_vertex_url(
                 custom_api_base=api_base,
                 vertex_location=vertex_location,

litellm/llms/vertex_ai/vertex_llm_base.py

@@ -49,8 +49,20 @@ class VertexBase:
         self.async_handler: Optional[AsyncHTTPHandler] = None
 
     def get_vertex_region(self, vertex_region: Optional[str], model: str) -> str:
-        if is_global_only_vertex_model(model):
-            return "global"
+        import litellm
+
+        # Try to get supported_regions directly from model_cost
+        # Check both with and without vertex_ai/ prefix
+        model_key = f"vertex_ai/{model}" if not model.startswith("vertex_ai/") else model
+        model_info = litellm.model_cost.get(model_key, {})
+        supported_regions = model_info.get("supported_regions")
+
+        if supported_regions and len(supported_regions) > 0:
+            # If user didn't specify region, use the first supported region
+            if vertex_region is None:
+                return supported_regions[0]
+            # If user specified a region, trust them
+            return vertex_region
         return vertex_region or "us-central1"
 
     def load_auth(