fix: apply server root path to mapped passthrough route matching

[umut-polat]

mapped passthrough routes (vertex_ai, bedrock, etc) were compared against the raw request path without prepending SERVER_ROOT_PATH. db-registered routes already used _build_full_path_with_root for this — the mapped routes branch was missed.

when a reverse proxy forwards /litellm/vertex_ai/... and SERVER_ROOT_PATH=/litellm, the route check fell through because it compared /litellm/vertex_ai/... against bare /vertex_ai.

one-line fix: run _build_full_path_with_root on each mapped route before the startswith check — same pattern already used 15 lines below for db routes.

test added covering prefixed and bare routes with a custom root.

fixes #22272

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Project	Deployment	Actions	Updated (UTC)
litellm	Ready	Preview, Comment	Feb 27, 2026 10:33pm

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[greptile-apps]

Greptile Summary

This PR fixes a bug where mapped pass-through routes (e.g., /vertex_ai, /bedrock) failed to match incoming requests when SERVER_ROOT_PATH is set to a non-root value (e.g., /litellm). The route check compared the prefixed request path /litellm/vertex_ai/... against the bare route /vertex_ai, causing a mismatch.

• Applies _build_full_path_with_root() to each mapped route before the startswith check in is_registered_pass_through_route(), matching the existing pattern used for DB-registered routes
• Adds a regression test that verifies both prefixed and bare route matching behavior with a custom SERVER_ROOT_PATH
• The fix is minimal (one line), well-scoped, and consistent with the existing codebase pattern

Confidence Score: 5/5

• This PR is safe to merge — it's a minimal, well-tested one-line fix that follows an existing pattern.
• The change is a single line that applies the same _build_full_path_with_root() helper already used 15 lines below for DB-registered routes. The fix is consistent with established patterns, the test covers the regression scenario with mocks (no network calls), and the scope is extremely narrow — only the mapped routes branch of is_registered_pass_through_route() is affected.
• No files require special attention

Important Files Changed

Filename	Overview
litellm/proxy/pass_through_endpoints/pass_through_endpoints.py	One-line fix applies _build_full_path_with_root to mapped pass-through routes, matching the pattern already used for DB-registered routes 15 lines below. Correct and consistent.
tests/test_litellm/proxy/pass_through_endpoints/test_pass_through_endpoints.py	Regression test verifies that mapped routes (vertex_ai, bedrock) match when SERVER_ROOT_PATH is set. Uses mocks only — no real network calls. Test covers both prefixed and bare routes.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["Incoming request<br>/litellm/vertex_ai/v1/projects/foo"] --> B["is_registered_pass_through_route(route)"]
    B --> C{"Check mapped routes<br>(vertex_ai, bedrock, etc.)"}
    C -->|"Before fix"| D["Compare: /litellm/vertex_ai/...<br>startswith /vertex_ai ❌"]
    D --> E["Falls through → 404"]
    C -->|"After fix"| F["_build_full_path_with_root(/vertex_ai)<br>→ /litellm/vertex_ai"]
    F --> G["Compare: /litellm/vertex_ai/...<br>startswith /litellm/vertex_ai ✅"]
    G --> H["Return True"]
    B --> I{"Check DB-registered routes<br>(already used _build_full_path_with_root)"}
    I --> J["Return True/False"]

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