fix(vertex_ai): use aiplatform.{geo}.rep.googleapis.com for multi-region locations

Vertex multi-region endpoints (e.g. us, eu) use the rep host pattern, not
{geo}-aiplatform.googleapis.com. Regional IDs still contain a hyphen.

common_utils.get_vertex_base_url centralizes the rule for SDK/API URL building.
Proxy pass-through duplicates the same branching in a local get_vertex_base_url
(with trailing slashes) to avoid importing from common_utils there; live
WebSocket passthrough uses the same multi-region host logic for wss://.

Tests cover us/eu for the common_utils helper.

Made-with: Cursor

litellm/llms/vertex_ai/common_utils.py

@@ -229,6 +229,10 @@ def get_vertex_base_url(
 ) -> str:
     """
     Get the base URL for Vertex AI API calls.
+
+    - ``global`` uses the global control plane host.
+    - Multi-region geographies (e.g. ``us``, ``eu``) use ``aiplatform.{geo}.rep.googleapis.com``.
+    - Regional locations (e.g. ``us-central1``) use ``{region}-aiplatform.googleapis.com``.
     """
     if vertex_location == "global":
         return "https://aiplatform.googleapis.com"
@@ -236,6 +240,8 @@ def get_vertex_base_url(
         raise ValueError("vertex_location is required")
     if not re.match(r"^[a-z][a-z0-9-]*$", vertex_location):
         raise ValueError("Invalid vertex_location format")
+    if "-" not in vertex_location:
+        return f"https://aiplatform.{vertex_location}.rep.googleapis.com"
     return f"https://{vertex_location}-aiplatform.googleapis.com"
 
 

litellm/proxy/pass_through_endpoints/llm_passthrough_endpoints.py

@@ -1497,7 +1497,9 @@ class VertexAIPassThroughHandler(BaseVertexAIPassThroughHandler):
 
 def get_vertex_base_url(vertex_location: Optional[str]) -> str:
     """
-    Returns the base URL for Vertex AI based on the provided location.
+    Base URL for Vertex AI pass-through (trailing slash for URL joining).
+
+    Keep location rules aligned with ``litellm.llms.vertex_ai.common_utils.get_vertex_base_url``.
     """
     if vertex_location == "global":
         return "https://aiplatform.googleapis.com/"
@@ -1505,6 +1507,8 @@ def get_vertex_base_url(vertex_location: Optional[str]) -> str:
         raise ValueError("vertex_location is required")
     if not re.match(r"^[a-z][a-z0-9-]*$", vertex_location):
         raise ValueError("Invalid vertex_location format")
+    if "-" not in vertex_location:
+        return f"https://aiplatform.{vertex_location}.rep.googleapis.com/"
     return f"https://{vertex_location}-aiplatform.googleapis.com/"
 
 
@@ -1708,7 +1712,8 @@ async def _base_vertex_proxy_route(
     Base function for Vertex AI passthrough routes.
     Handles common logic for all Vertex AI services.
 
-    Default base_target_url is `https://{vertex_location}-aiplatform.googleapis.com/`
+    Default base_target_url is derived from ``get_vertex_base_url`` in this module
+    (regional, ``global``, or multi-region ``.rep.`` hosts), with a trailing slash.
 
     Args:
         endpoint: The endpoint path
@@ -2280,11 +2285,7 @@ async def vertex_ai_live_websocket_passthrough(
         return
 
     host_location = resolved_location or vertex_llm_base.get_default_vertex_location()
-    host = (
-        "aiplatform.googleapis.com"
-        if host_location == "global"
-        else f"{host_location}-aiplatform.googleapis.com"
-    )
+    host = get_vertex_base_url(host_location).removeprefix("https://").rstrip("/")
     service_url = (
         f"wss://{host}/ws/google.cloud.aiplatform.v1.LlmBidiService/BidiGenerateContent"
     )

tests/test_litellm/llms/vertex_ai/test_vertex_global_url_support.py

@@ -5,6 +5,7 @@ This test suite ensures that all Vertex AI endpoints properly handle the 'global
 which uses a different URL format than regional endpoints.
 
 Regional: https://{region}-aiplatform.googleapis.com/...
+Multi-region: https://aiplatform.{geo}.rep.googleapis.com/...
 Global: https://aiplatform.googleapis.com/...
 """
 
@@ -30,6 +31,8 @@ class TestVertexBaseURL:
             ("europe-west1", "https://europe-west1-aiplatform.googleapis.com"),
             ("asia-northeast1", "https://asia-northeast1-aiplatform.googleapis.com"),
             ("global", "https://aiplatform.googleapis.com"),
+            ("us", "https://aiplatform.us.rep.googleapis.com"),
+            ("eu", "https://aiplatform.eu.rep.googleapis.com"),
         ],
     )
     def test_get_vertex_base_url(self, vertex_location, expected_base_url):

tests/test_litellm/proxy/pass_through_endpoints/test_llm_pass_through_endpoints.py

@@ -21,6 +21,7 @@ from litellm.proxy.pass_through_endpoints.llm_passthrough_endpoints import (
     bedrock_llm_proxy_route,
     create_pass_through_route,
     cursor_proxy_route,
+    get_vertex_base_url,
     llm_passthrough_factory_proxy_route,
     milvus_proxy_route,
     openai_proxy_route,
@@ -31,6 +32,35 @@ from litellm.proxy.pass_through_endpoints.llm_passthrough_endpoints import (
 from litellm.types.passthrough_endpoints.vertex_ai import VertexPassThroughCredentials
 
 
+class TestVertexPassthroughGetVertexBaseUrl:
+    """Module-local get_vertex_base_url (trailing slash); rules match common_utils."""
+
+    @pytest.mark.parametrize(
+        "vertex_location, expected",
+        [
+            ("global", "https://aiplatform.googleapis.com/"),
+            ("us-central1", "https://us-central1-aiplatform.googleapis.com/"),
+            ("us", "https://aiplatform.us.rep.googleapis.com/"),
+            ("eu", "https://aiplatform.eu.rep.googleapis.com/"),
+        ],
+    )
+    def test_returns_base_with_trailing_slash(self, vertex_location, expected):
+        assert get_vertex_base_url(vertex_location) == expected
+
+    @pytest.mark.parametrize(
+        "vertex_location, expected_host",
+        [
+            ("global", "aiplatform.googleapis.com"),
+            ("us-central1", "us-central1-aiplatform.googleapis.com"),
+            ("us", "aiplatform.us.rep.googleapis.com"),
+            ("eu", "aiplatform.eu.rep.googleapis.com"),
+        ],
+    )
+    def test_websocket_host_strips_scheme(self, vertex_location, expected_host):
+        host = get_vertex_base_url(vertex_location).removeprefix("https://").rstrip("/")
+        assert host == expected_host
+
+
 class TestBaseOpenAIPassThroughHandler:
     def test_join_url_paths(self):
         print("\nTesting _join_url_paths method...")