fix: url construction for trailing v1 base urls

[rohan-shettyy]

Relevant issues

Fixes #26009

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CI (LiteLLM team)

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• 45-49 passing tests: acceptable but needs attention
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Screenshots / Proof of Fix

Before fix: test failing

PASS: https://api.openai.com                    -> https://api.openai.com/v1/models
PASS: https://api.openai.com/v1                 -> https://api.openai.com/v1/models
FAIL: https://opencode.ai/zen/v1                -> https://opencode.ai/v1/models
      expected                                   -> https://opencode.ai/zen/v1/models
FAIL: https://opencode.ai/zen                   -> https://opencode.ai/v1/models
      expected                                   -> https://opencode.ai/zen/v1/models
PASS: http://localhost:11434/v1                 -> http://localhost:11434/v1/models

After fix: tests passing

tests/litellm/llms/test_openai_get_models_url.py::TestGetModelsUrl::test_plain_base_url PASSED [ 11%]
tests/litellm/llms/test_openai_get_models_url.py::TestGetModelsUrl::test_trailing_slash PASSED [ 22%]
tests/litellm/llms/test_openai_get_models_url.py::TestGetModelsUrl::test_v1_already_present PASSED [ 33%]
tests/litellm/llms/test_openai_get_models_url.py::TestGetModelsUrl::test_v1_with_trailing_slash PASSED [ 44%]
tests/litellm/llms/test_openai_get_models_url.py::TestGetModelsUrl::test_subpath_with_v1 PASSED [ 55%]
tests/litellm/llms/test_openai_get_models_url.py::TestGetModelsUrl::test_subpath_with_v1_trailing_slash PASSED [ 66%]
tests/litellm/llms/test_openai_get_models_url.py::TestGetModelsUrl::test_subpath_without_v1 PASSED [ 77%]
tests/litellm/llms/test_openai_get_models_url.py::TestGetModelsUrl::test_localhost_with_port_and_v1 PASSED [ 88%]
tests/litellm/llms/test_openai_get_models_url.py::TestGetModelsUrl::test_localhost_without_v1 PASSED [100%]

Type

🐛 Bug Fix

Changes

Fix: Preserves sub-paths in api_base and avoids duplicate /v1 segments when calling get_models() in OpenAIGPTConfig. Fixes #26009.
Tests: Adds unit tests for get_models() URL construction across multiple api_base formats.

[greptile-apps]

Greptile Summary

This PR fixes a URL construction bug in OpenAIGPTConfig.get_models() where a custom api_base containing a sub-path (e.g. https://opencode.ai/zen/v1) would have /v1/models naively appended, resulting in a duplicate /v1 segment or a missing sub-path. The fix strips trailing slashes then checks whether the base already ends with /v1 before deciding whether to append /models or /v1/models, and a new test file covers nine URL permutations.

Confidence Score: 5/5

Safe to merge — targeted one-method fix with comprehensive mock-based test coverage.

The change is isolated to a single method, the logic is straightforward and correct, all test cases pass and are properly mocked (no live network calls), and no existing tests were modified.

No files require special attention.

Important Files Changed

Filename	Overview
litellm/llms/openai/chat/gpt_transformation.py	Added trailing-slash strip + /v1-awareness to get_models() URL construction; change is minimal and correct.
tests/litellm/llms/test_openai_get_models_url.py	New test file covering nine URL scenarios for get_models(); all calls are properly mocked with no real network requests.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A["get_models(api_key, api_base)"] --> B{api_base is None?}
    B -->|Yes| C["api_base = 'https://api.openai.com'"]
    B -->|No| D["use provided api_base"]
    C --> E["strip trailing '/'"]
    D --> E
    E --> F{ends with '/v1'?}
    F -->|Yes| G["url = api_base + '/models'"]
    F -->|No| H["url = api_base + '/v1/models'"]
    G --> I["GET url with Bearer token"]
    H --> I
    I --> J{status 200?}
    J -->|Yes| K["return model IDs"]
    J -->|No| L["raise Exception"]

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_{Reviews (2): Last reviewed commit: "add tests for edge cases" | Re-trigger Greptile}

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
litellm/llms/openai/chat/gpt_transformation.py	75.00%	1 Missing ⚠️

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