feat(github_copilot): route /v1/messages to Copilot native Anthropic endpoint

Add a GitHub Copilot Anthropic Messages transformation that routes supported Claude models through the native /v1/messages endpoint. This covers request URL construction, default headers, and supported model metadata.

litellm/llms/github_copilot/messages/transformation.py

@@ -0,0 +1,81 @@
+from typing import Any, List, Optional, Tuple
+
+from litellm.exceptions import AuthenticationError
+from litellm.llms.anthropic.experimental_pass_through.messages.transformation import (
+    AnthropicMessagesConfig,
+)
+
+from ..authenticator import Authenticator
+from ..common_utils import (
+    DEFAULT_GITHUB_COPILOT_API_BASE,
+    GetAPIKeyError,
+    get_copilot_default_headers,
+)
+
+
+class GithubCopilotAnthropicMessagesConfig(AnthropicMessagesConfig):
+    """
+    GitHub Copilot implementation of Anthropic messages API.
+    Routes requests to Copilot's /v1/messages endpoint with appropriate authentication and headers.
+    """
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.authenticator = Authenticator()
+
+    def validate_anthropic_messages_environment(
+        self,
+        headers: dict,
+        model: str,
+        messages: List[Any],
+        optional_params: dict,
+        litellm_params: dict,
+        api_key: Optional[str] = None,
+        api_base: Optional[str] = None,
+    ) -> Tuple[dict, Optional[str]]:
+        """
+        Validate environment for GitHub Copilot and add Copilot-specific headers.
+        """
+        # Get Copilot auth credentials
+        dynamic_api_base = (
+            api_base
+            or self.authenticator.get_api_base()
+            or DEFAULT_GITHUB_COPILOT_API_BASE
+        )
+        try:
+            dynamic_api_key = self.authenticator.get_api_key()
+        except GetAPIKeyError as e:
+            raise AuthenticationError(
+                model=model,
+                llm_provider="github_copilot",
+                message=str(e),
+            )
+
+        # Merge Copilot headers with provided headers
+        copilot_headers = get_copilot_default_headers(dynamic_api_key)
+        for key, value in copilot_headers.items():
+            if key not in headers:
+                headers[key] = value
+
+        # Set Anthropic version for messages API
+        if "anthropic-version" not in headers:
+            headers["anthropic-version"] = "2023-06-01"
+
+        return headers, dynamic_api_base
+
+    def get_complete_url(
+        self,
+        api_base: Optional[str],
+        api_key: Optional[str],
+        model: str,
+        optional_params: dict,
+        litellm_params: dict,
+        stream: Optional[bool] = None,
+    ) -> str:
+        """
+        Return the complete URL for GitHub Copilot /v1/messages endpoint.
+        """
+        api_base = api_base or DEFAULT_GITHUB_COPILOT_API_BASE
+        if not api_base.endswith("/v1/messages"):
+            api_base = f"{api_base}/v1/messages"
+        return api_base

litellm/model_prices_and_context_window_backup.json

@@ -18951,7 +18951,8 @@
         "max_tokens": 16000,
         "mode": "chat",
         "supported_endpoints": [
-            "/v1/chat/completions"
+            "/v1/chat/completions",
+            "/v1/messages"
         ],
         "supports_function_calling": true,
         "supports_parallel_function_calling": true,
@@ -18964,7 +18965,8 @@
         "max_tokens": 16000,
         "mode": "chat",
         "supported_endpoints": [
-            "/v1/chat/completions"
+            "/v1/chat/completions",
+            "/v1/messages"
         ],
         "supports_function_calling": true,
         "supports_parallel_function_calling": true,
@@ -19015,7 +19017,8 @@
         "max_tokens": 16000,
         "mode": "chat",
         "supported_endpoints": [
-            "/v1/chat/completions"
+            "/v1/chat/completions",
+            "/v1/messages"
         ],
         "supports_function_calling": true,
         "supports_parallel_function_calling": true,

litellm/utils.py

@@ -8893,6 +8893,13 @@ class ProviderConfigManager:
             )
 
             return DeepSeekAnthropicMessagesConfig()
+        elif litellm.LlmProviders.GITHUB_COPILOT == provider:
+            if "claude" in model_lower:
+                from litellm.llms.github_copilot.messages.transformation import (
+                    GithubCopilotAnthropicMessagesConfig,
+                )
+
+                return GithubCopilotAnthropicMessagesConfig()
         return None
 
     @staticmethod

tests/test_litellm/llms/github_copilot/messages/test_github_copilot_messages_transformation.py

@@ -0,0 +1,117 @@
+import os
+import sys
+from unittest.mock import MagicMock
+
+import pytest
+
+sys.path.insert(0, os.path.abspath("../.."))
+
+from litellm.llms.github_copilot.messages.transformation import (
+    GithubCopilotAnthropicMessagesConfig,
+)
+from litellm.llms.github_copilot.common_utils import GetAPIKeyError
+
+
+def test_github_copilot_anthropic_messages_config_init():
+    """Test GithubCopilotAnthropicMessagesConfig initialization."""
+    config = GithubCopilotAnthropicMessagesConfig()
+    assert config is not None
+    assert hasattr(config, "authenticator")
+
+
+def test_github_copilot_anthropic_messages_get_complete_url():
+    """Test URL construction for GitHub Copilot messages endpoint."""
+    config = GithubCopilotAnthropicMessagesConfig()
+
+    # Test with default api_base
+    url = config.get_complete_url(
+        api_base=None,
+        api_key=None,
+        model="github_copilot/claude-haiku-4.5",
+        optional_params={},
+        litellm_params={},
+    )
+    assert url == "https://api.githubcopilot.com/v1/messages"
+
+    # Test with custom api_base
+    url = config.get_complete_url(
+        api_base="https://custom.api.com",
+        api_key=None,
+        model="github_copilot/claude-haiku-4.5",
+        optional_params={},
+        litellm_params={},
+    )
+    assert url == "https://custom.api.com/v1/messages"
+
+    # Test with api_base already ending with /v1/messages
+    url = config.get_complete_url(
+        api_base="https://custom.api.com/v1/messages",
+        api_key=None,
+        model="github_copilot/claude-haiku-4.5",
+        optional_params={},
+        litellm_params={},
+    )
+    assert url == "https://custom.api.com/v1/messages"
+
+
+def test_github_copilot_anthropic_messages_validate_environment():
+    """Test environment validation and header injection."""
+    config = GithubCopilotAnthropicMessagesConfig()
+
+    # Mock the authenticator
+    config.authenticator = MagicMock()
+    config.authenticator.get_api_key.return_value = "gh.test-key-123"
+    config.authenticator.get_api_base.return_value = None
+
+    headers = {}
+    validated_headers, api_base = config.validate_anthropic_messages_environment(
+        headers=headers,
+        model="github_copilot/claude-haiku-4.5",
+        messages=[{"role": "user", "content": "Hello"}],
+        optional_params={},
+        litellm_params={},
+        api_key=None,
+        api_base=None,
+    )
+
+    # Check that Copilot headers were added
+    assert "copilot-integration-id" in validated_headers
+    assert validated_headers["copilot-integration-id"] == "vscode-chat"
+    assert "Authorization" in validated_headers
+    assert "anthropic-version" in validated_headers
+    assert validated_headers["anthropic-version"] == "2023-06-01"
+    assert api_base == "https://api.githubcopilot.com"
+
+
+def test_github_copilot_anthropic_messages_validate_environment_auth_error():
+    """Test error handling when authentication fails."""
+    config = GithubCopilotAnthropicMessagesConfig()
+
+    # Mock the authenticator to raise an error
+    config.authenticator = MagicMock()
+    config.authenticator.get_api_key.side_effect = GetAPIKeyError(
+        status_code=401, message="No valid API key found"
+    )
+
+    with pytest.raises(Exception):  # AuthenticationError
+        config.validate_anthropic_messages_environment(
+            headers={},
+            model="github_copilot/claude-haiku-4.5",
+            messages=[{"role": "user", "content": "Hello"}],
+            optional_params={},
+            litellm_params={},
+            api_key=None,
+            api_base=None,
+        )
+
+
+def test_github_copilot_anthropic_messages_supported_params():
+    """Test supported parameters list."""
+    config = GithubCopilotAnthropicMessagesConfig()
+    params = config.get_supported_anthropic_messages_params("github_copilot/claude-haiku-4.5")
+
+    # Should inherit from AnthropicMessagesConfig
+    assert "messages" in params
+    assert "model" in params
+    assert "max_tokens" in params
+    assert "thinking" in params