feat(vertex_ai): multi-region Vertex hosts (aiplatform.*.rep.googleapis.com)

[milan-berri]

Relevant issues

Fixes #25926

Reference: Multi-region endpoints for Claude on Vertex AI (Google Cloud Blog)

Pre-Submission checklist

Please complete all items before asking a LiteLLM maintainer to review your PR

• I have Added testing in the tests/test_litellm/ directory, Adding at least 1 test is a hard requirement - see details
• My PR passes all unit tests on make test-unit
• My PR's scope is as isolated as possible, it only solves 1 specific problem
• I have requested a Greptile review by commenting @greptileai and received a Confidence Score of at least 4/5 before requesting a maintainer review

CI (LiteLLM team)

CI status guideline:

• 50-55 passing tests: main is stable with minor issues.
• 45-49 passing tests: acceptable but needs attention
• <= 40 passing tests: unstable; be careful with your merges and assess the risk.

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Type

🆕 New Feature
✅ Test

Changes

• litellm/llms/vertex_ai/common_utils.py — get_vertex_base_url: After global, treat locations that are truthy and contain no - as Vertex multi-region hosts (https://aiplatform.{geo}.rep.googleapis.com). Otherwise keep the regional pattern https://{region}-aiplatform.googleapis.com (preserves prior behavior for None / empty via the final branch).
• litellm/proxy/pass_through_endpoints/llm_passthrough_endpoints.py: Local get_vertex_base_url duplicates the same rules with trailing slashes for URL joining (no import from common_utils). WebSocket upstream host for Vertex live passthrough uses the same multi-region vs regional logic so us / eu work for wss://.
• tests/test_litellm/llms/vertex_ai/test_vertex_global_url_support.py: Parametrize us and eu expected base URLs for get_vertex_base_url.

[greptile-apps]

Greptile Summary

This PR adds support for Vertex AI multi-region endpoints (aiplatform.{geo}.rep.googleapis.com) by detecting single-token locations (no -) that are not global and routing them to the .rep. host pattern. The feature covers both the SDK path (common_utils.get_vertex_base_url) and the proxy pass-through + WebSocket paths in llm_passthrough_endpoints.py, with unit tests for both.

Confidence Score: 5/5

Safe to merge — the change is minimal, backward-compatible, and well-tested with mocked unit tests.

All remaining findings are P2 (style/test-coverage suggestions). The core routing logic is correct, existing behavior is preserved, the WebSocket host derivation is simplified by reusing the helper, and the new test classes exercise all four location categories.

No files require special attention.

Important Files Changed

Filename	Overview
litellm/llms/vertex_ai/common_utils.py	Adds multi-region branch ("-" not in vertex_location) to get_vertex_base_url; logic is minimal and backward-compatible
litellm/proxy/pass_through_endpoints/llm_passthrough_endpoints.py	Mirrors the same multi-region branch in the local get_vertex_base_url (trailing-slash variant) and simplifies the WebSocket host derivation by reusing it
tests/test_litellm/llms/vertex_ai/test_vertex_global_url_support.py	Adds us and eu parametrized cases to the existing TestVertexBaseURL suite; all tests are mocked, no network calls
tests/test_litellm/proxy/pass_through_endpoints/test_llm_pass_through_endpoints.py	Adds a new TestVertexPassthroughGetVertexBaseUrl class covering base URL and WebSocket host stripping for all four location types

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[vertex_location input] --> B{equals global?}
    B -- Yes --> C["https://aiplatform.googleapis.com"]
    B -- No --> D{is None?}
    D -- Yes --> E[raise ValueError]
    D -- No --> F{passes format regex?}
    F -- No --> G[raise ValueError]
    F -- Yes --> H{contains a dash?}
    H -- No --> I["multi-region: aiplatform.geo.rep.googleapis.com\nus, eu, ..."]
    H -- Yes --> J["regional: region-aiplatform.googleapis.com\nus-central1, europe-west1, ..."]

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_{Reviews (2): Last reviewed commit: "fix(vertex_ai): use aiplatform.{geo}.rep..." | Re-trigger Greptile}

[mateo-berri]

LGTM. Appreciate it!

[veria-ai]

Low: No security issues found

This PR adds multi-region Vertex AI host support by branching on whether vertex_location contains a hyphen. Both get_vertex_base_url functions (in common_utils.py and llm_passthrough_endpoints.py) apply a strict regex validation (^[a-z][a-z0-9-]*$) before interpolating the location into URLs, and all generated URLs remain under googleapis.com. The websocket path also routes through the same validated function. No new attack surface is introduced.

---

Status: 0 open
Risk: 2/10

Posted by Veria AI · 2026-04-23T22:14:57.488Z

[codecov]

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