Fix/GitHub copilot vision headers

[krozbicki]

Title

feat: Add base_llm_http_handler support for GitHub Copilot chat completions

Relevant issues

Fixes #14496

Pre-Submission checklist

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

• I have Added testing in the tests/litellm/ directory
• I have added a screenshot of my new test passing locally
• 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

Type

✨ Feature / 🐛 Bug Fix

Changes

Problem

1. Vision requests failing: GitHub Copilot vision requests were failing with a 400 Bad Request error due to missing Copilot-Vision-Request header
2. No base_llm_http_handler support: GitHub Copilot couldn't work with the new base_llm_http_handler routing when EXPERIMENTAL_OPENAI_BASE_LLM_HTTP_HANDLER flag is enabled

Solution

1. Enhanced validate_environment() (fixes vision requests)

Extended the validate_environment() method in GithubCopilotConfig to add GitHub Copilot-specific headers:

• Enhanced validate_environment() in GithubCopilotConfig (litellm/llms/github_copilot/chat/transformation.py)
  • Calls super().validate_environment() to get base OpenAI headers (Authorization, Content-Type)
  • Adds X-Initiator header based on message roles:
    • Returns "agent" if any message has role "tool" or "assistant"
    • Returns "user" otherwise
  • Adds Copilot-Vision-Request: true header when image content is detected:
    • Checks for image_url in message content
    • Checks for content items with type: "image_url"

2. Add base_llm_http_handler support

Enabled GitHub Copilot to work with the new base_llm_http_handler routing mechanism:

• Added get_complete_url() method to construct full endpoint URL

  • Returns: https://api.githubcopilot.com/chat/completions
  • Supports dynamic api_base from authenticator
  • Handles trailing slash normalization

• Added custom_llm_provider property returning LlmProviders.GITHUB_COPILOT

  • Ensures correct provider identification in routing logic

• Simplified __init__() method

  • Removed 3 unused parameters: api_key, api_base, custom_llm_provider
  • These were dead code as the property always overrides parameter value
  • Aligns with patterns from 30+ other providers in the codebase

• Fixed test to use mock_response parameter

  • test_completion_github_copilot_mock_response now uses mock_response instead of patching
  • More robust and simpler test implementation

Impact

• Minimal & Isolated: Changes only affect GitHub Copilot provider
• Backward Compatible: Works with both standard routing and new base_llm_http_handler
• Feature Complete:
  • ✅ Vision requests now work properly
  • ✅ Compatible with EXPERIMENTAL_OPENAI_BASE_LLM_HTTP_HANDLER flag
  • ✅ Maintains all existing functionality

Test Results

======================================== test session starts ========================================
platform linux -- Python 3.10.12, pytest-7.4.4, pluggy-1.5.0 -- /home/krzysiek/projects/litellm/.venv/bin/python
cachedir: .pytest_cache
rootdir: /home/krzysiek/projects/litellm
configfile: pyproject.toml
plugins: mock-3.14.1, asyncio-0.21.2, respx-0.22.0, requests-mock-1.12.1, anyio-4.5.2
asyncio: mode=auto
collected 20 items

tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_completion_github_copilot_mock_response PASSED [  5%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_copilot_vision_request_header_text_only PASSED [ 10%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_copilot_vision_request_header_with_image PASSED [ 15%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_copilot_vision_request_header_with_type_image_url PASSED [ 20%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_custom_llm_provider_property PASSED [ 25%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_get_complete_url_strips_trailing_slash PASSED [ 30%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_get_complete_url_with_authenticator_api_base PASSED [ 35%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_get_complete_url_with_custom_api_base PASSED [ 40%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_get_complete_url_with_default_api_base PASSED [ 45%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_get_supported_openai_params_case_insensitive PASSED [ 50%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_get_supported_openai_params_claude_model PASSED [ 55%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_github_copilot_config_get_openai_compatible_provider_info PASSED [ 60%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_transform_messages_disable_copilot_system_to_assistant PASSED [ 65%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_x_initiator_header_agent_request_with_assistant PASSED [ 70%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_x_initiator_header_agent_request_with_tool PASSED [ 75%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_x_initiator_header_empty_messages PASSED [ 80%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_x_initiator_header_mixed_messages_with_agent_roles PASSED [ 85%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_x_initiator_header_system_only_messages PASSED [ 90%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_x_initiator_header_user_only_messages PASSED [ 95%]
tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py::test_x_initiator_header_user_request PASSED [100%]

================================== 20 passed, 3 warnings in 0.98s ===================================

All 20 tests passing:

• 13 existing tests (vision headers, X-Initiator header logic, message transformation, Claude parameter support, etc.)
• 6 new tests added in this PR:
  • test_custom_llm_provider_property - verifies property returns correct provider
  • test_get_complete_url_with_default_api_base - default URL construction
  • test_get_complete_url_with_custom_api_base - custom api_base handling
  • test_get_complete_url_with_authenticator_api_base - dynamic api_base from authenticator
  • test_get_complete_url_strips_trailing_slash - trailing slash normalization
• 1 modified test:
  • test_completion_github_copilot_mock_response - now uses mock_response parameter instead of patching

Type checking: mypy passes with no issues

Files Changed

• litellm/llms/github_copilot/chat/transformation.py - Enhanced validate_environment(), added get_complete_url(), custom_llm_provider property, simplified __init__()
• tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py - Added 6 new tests, modified 1 existing test

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Project	Deployment	Preview	Comments	Updated (UTC)
litellm	Ready	Preview	Comment	Dec 2, 2025 8:50pm