fix(azure_ai): only reclassify as azure when api_base is a classic Azure OpenAI endpoint

litellm/llms/azure_ai/chat/transformation.py

@@ -207,20 +207,22 @@ class AzureAIStudioConfig(OpenAIConfig):
                 message["content"] = texts
         return stripped_messages
 
-    def _is_azure_openai_model(self, model: str, api_base: str | None) -> bool:
-        try:
-            if "/" in model:
-                model = model.split("/", 1)[1]
-            if (
-                model in litellm.open_ai_chat_completion_models
-                or model in litellm.open_ai_text_completion_models
-                or model in litellm.open_ai_embedding_models
-            ):
-                return True
-
-        except Exception:
+    def _is_foundry_model_inference_base(self, api_base: str) -> bool:
+        parsed: Final = urlparse(api_base)
+        host: Final = parsed.hostname
+        if host is None or not host.endswith(".services.ai.azure.com"):
             return False
-        return False
+        return "/openai/deployments" not in parsed.path
+
+    def _is_azure_openai_model(self, model: str, api_base: str | None) -> bool:
+        if api_base is None or self._is_foundry_model_inference_base(api_base):
+            return False
+        stripped_model: Final = model.split("/", 1)[1] if "/" in model else model
+        return (
+            stripped_model in litellm.open_ai_chat_completion_models
+            or stripped_model in litellm.open_ai_text_completion_models
+            or stripped_model in litellm.open_ai_embedding_models
+        )
 
     def _get_openai_compatible_provider_info(
         self,

tests/test_litellm/llms/azure_ai/chat/test_azure_ai_transformation.py

@@ -31,6 +31,46 @@ async def test_get_openai_compatible_provider_info():
     assert custom_llm_provider == "azure"
 
 
+@pytest.mark.parametrize(
+    "model, api_base, expected_provider",
+    [
+        ("azure_ai/gpt-4o", "https://my-resource.services.ai.azure.com", "azure_ai"),
+        ("azure_ai/gpt-4o", "https://my-resource.services.ai.azure.com/models", "azure_ai"),
+        ("azure_ai/gpt-5.4-nano", "https://my-resource.services.ai.azure.com", "azure_ai"),
+        ("azure_ai/gpt-4o", "https://my-resource.openai.azure.com", "azure"),
+        (
+            "azure_ai/gpt-4o",
+            "https://my-resource.services.ai.azure.com/openai/deployments/gpt-4o/chat/completions"
+            "?api-version=2024-08-01-preview",
+            "azure",
+        ),
+        ("azure_ai/mistral-large-latest", "https://my-resource.services.ai.azure.com", "azure_ai"),
+        ("azure_ai/mistral-large-latest", "https://my-resource.openai.azure.com", "azure_ai"),
+    ],
+)
+def test_foundry_base_keeps_azure_ai_provider(model: str, api_base: str, expected_provider: str):
+    """Regression for #38276: a Foundry .services.ai.azure.com base must not be reclassified as azure."""
+    config = AzureAIStudioConfig()
+    (
+        _,
+        _,
+        custom_llm_provider,
+    ) = config._get_openai_compatible_provider_info(
+        model=model,
+        api_base=api_base,
+        api_key="my-key",
+        custom_llm_provider="azure_ai",
+    )
+    assert custom_llm_provider == expected_provider
+
+
+def test_is_azure_openai_model_without_api_base_keeps_azure_ai():
+    """Metadata lookups (get_model_info, supports_* checks) carry no api_base and must not flip the provider."""
+    config = AzureAIStudioConfig()
+    assert config._is_azure_openai_model(model="azure_ai/gpt-4o", api_base=None) is False
+    assert config._is_azure_openai_model(model="azure_ai/gpt-4o", api_base="https://my-res.openai.azure.com") is True
+
+
 def test_azure_ai_validate_environment():
     config = AzureAIStudioConfig()
     headers = config.validate_environment(

tests/test_litellm/test_gpt_5_5_model_metadata.py

@@ -47,8 +47,7 @@ def test_azure_ai_gpt_5_5_model_info(model):
 
     routed_model, provider, _, _ = get_llm_provider(model=model)
     assert routed_model == model.split("/", 1)[1]
-    # azure_ai/* models resolve under the azure provider in get_llm_provider
-    assert provider == "azure"
+    assert provider == "azure_ai"
 
 
 def test_azure_ai_gpt_5_5_backup_matches_main():