fix(vertex-ai): warn on region override and remove dead is_global_only_vertex_model

Add verbose_logger.warning when user-specified region is overridden by
supported_regions. Remove now-unused is_global_only_vertex_model function
and its tests since get_vertex_region handles all region logic directly.

litellm/llms/vertex_ai/common_utils.py

@@ -940,25 +940,6 @@ def construct_target_url(
     return updated_url
 
 
-def is_global_only_vertex_model(model: str) -> bool:
-    """
-    Check if a model is only available in the global region.
-
-    Args:
-        model: The model name to check
-
-    Returns:
-        True if the model is only available in global region, False otherwise
-    """
-    from litellm.utils import get_supported_regions
-
-    supported_regions = get_supported_regions(
-        model=model, custom_llm_provider="vertex_ai"
-    )
-    if supported_regions is None:
-        return False
-    return "global" in supported_regions
-
 
 class VertexAIModelInfo(BaseLLMModelInfo):
     def get_token_counter(self) -> Optional[BaseTokenCounter]:

litellm/llms/vertex_ai/vertex_llm_base.py

@@ -62,6 +62,11 @@ class VertexBase:
                 return supported_regions[0]
             # If user specified a region not supported by this model, override it
             if vertex_region not in supported_regions:
+                verbose_logger.warning(
+                    "Vertex AI model '%s' does not support region '%s' "
+                    "(supported: %s). Routing to '%s'.",
+                    model, vertex_region, supported_regions, supported_regions[0],
+                )
                 return supported_regions[0]
             return vertex_region
         return vertex_region or "us-central1"

tests/test_litellm/llms/vertex_ai/test_vertex_ai_common_utils.py

@@ -558,34 +558,6 @@ def test_get_vertex_url_global_region(stream, expected_endpoint_suffix):
     assert url == expected_url
 
 
-@pytest.mark.parametrize(
-    "supported_regions, expected_result",
-    [
-        (None, False),  # get_supported_regions returns None
-        ([], False),  # empty list, no global region
-        (["us-central1"], False),  # only regional, no global
-        (["global"], True),  # only global region
-        (["global", "us-central1"], True),  # global and other regions
-        (
-            ["us-central1", "global", "europe-west1"],
-            True,
-        ),  # global among multiple regions
-    ],
-)
-def test_is_global_only_vertex_model(supported_regions, expected_result):
-    """Test is_global_only_vertex_model with various supported regions scenarios"""
-    from litellm.llms.vertex_ai.common_utils import is_global_only_vertex_model
-
-    with patch("litellm.utils.get_supported_regions") as mock_get_supported_regions:
-        mock_get_supported_regions.return_value = supported_regions
-
-        result = is_global_only_vertex_model("test-model")
-
-        assert result == expected_result
-        mock_get_supported_regions.assert_called_once_with(
-            model="test-model", custom_llm_provider="vertex_ai"
-        )
-
 
 @pytest.mark.parametrize(
     "model_cost_entry, vertex_region, expected_region",

tests/test_litellm/llms/vertex_ai/vertex_ai_partner_models/qwen/test_vertex_ai_qwen_global_endpoint.py

@@ -2,8 +2,8 @@
 Tests for Vertex AI Qwen MaaS models that require the global endpoint.
 
 These tests verify that:
-1. Qwen models are correctly identified as global-only models
-2. The correct global URL is constructed (https://aiplatform.googleapis.com)
+1. The correct global URL is constructed (https://aiplatform.googleapis.com)
+2. The get_vertex_region method resolves regions from model_cost supported_regions
 3. The completion() and responses() API work with Qwen models
 """
 
@@ -19,7 +19,6 @@ sys.path.insert(
 )  # Adds the parent directory to the system path
 
 import litellm
-from litellm.llms.vertex_ai.common_utils import is_global_only_vertex_model
 from litellm.llms.vertex_ai.vertex_llm_base import VertexBase
 from litellm.types.llms.vertex_ai import VertexPartnerProvider
 
@@ -48,38 +47,6 @@ def clean_vertex_env():
         os.environ[var] = value
 
 
-class TestQwenGlobalOnlyDetection:
-    """Test that Qwen models are correctly identified as global-only."""
-
-    @pytest.mark.parametrize(
-        "model",
-        [
-            "vertex_ai/qwen/qwen3-next-80b-a3b-instruct-maas",
-            "vertex_ai/qwen/qwen3-next-80b-a3b-thinking-maas",
-            "vertex_ai/qwen/qwen3-235b-a22b-instruct-2507-maas",
-            "vertex_ai/qwen/qwen3-coder-480b-a35b-instruct-maas",
-        ],
-    )
-    def test_qwen_models_are_global_only(self, model):
-        """Test that Qwen MaaS models are identified as global-only."""
-        # This test requires the model_cost to have supported_regions: ["global"]
-        # If the model is not in model_cost, it should return False (fallback behavior)
-        result = is_global_only_vertex_model(model)
-        # Note: This will return True only if the model is in model_cost with supported_regions: ["global"]
-        # If running without the updated model_cost, this may return False
-        assert isinstance(result, bool)
-
-    def test_non_global_model_returns_false(self):
-        """Test that non-global models return False."""
-        result = is_global_only_vertex_model("vertex_ai/gemini-1.5-pro")
-        assert result is False
-
-    def test_unknown_model_returns_false(self):
-        """Test that unknown models return False (fallback behavior)."""
-        result = is_global_only_vertex_model("vertex_ai/unknown-model-xyz")
-        assert result is False
-
-
 class TestVertexBaseGetVertexRegion:
     """Test the get_vertex_region method using model_cost lookup."""