feat: Add thinking and reasoning_effort parameter support for GitHub Copilot provider

- Add github_copilot case to get_supported_openai_params function
- Implement get_supported_openai_params method in GithubCopilotConfig
- Dynamically add thinking and reasoning_effort params for Anthropic models
- Add comprehensive tests for parameter support validation
- Ensure case-insensitive model detection for parameter inclusion

Fixes UnsupportedParamsError when using advanced reasoning parameters
with Anthropic models through GitHub Copilot proxy.

litellm/litellm_core_utils/get_supported_openai_params.py

@@ -271,6 +271,8 @@ def get_supported_openai_params(  # noqa: PLR0915
                     model=model
                 )
             )
+    elif custom_llm_provider == "github_copilot":
+        return litellm.GithubCopilotConfig().get_supported_openai_params(model=model)
     elif custom_llm_provider in litellm._custom_providers:
         if request_type == "chat_completion":
             provider_config = litellm.ProviderConfigManager.get_provider_chat_config(

litellm/llms/github_copilot/chat/transformation.py

@@ -77,6 +77,22 @@ class GithubCopilotConfig(OpenAIConfig):
 
         return validated_headers
 
+    def get_supported_openai_params(self, model: str) -> list:
+        """
+        Get supported OpenAI parameters for GitHub Copilot.
+        
+        For Anthropic models (like claude-sonnet-4), includes thinking and reasoning parameters.
+        For other models, returns standard OpenAI parameters.
+        """
+        # Get base OpenAI parameters
+        base_params = super().get_supported_openai_params(model)
+        
+        # Add thinking and reasoning parameters for Anthropic Claude models
+        if "claude" in model.lower():
+            base_params.extend(["thinking", "reasoning_effort"])
+        
+        return base_params
+
     def _determine_initiator(self, messages: List[AllMessageValues]) -> str:
         """
         Determine if request is user or agent initiated based on message roles.

tests/test_litellm/llms/github_copilot/test_github_copilot_transformation.py

@@ -362,3 +362,43 @@ def test_x_initiator_header_system_only_messages():
     )
     
     assert headers["X-Initiator"] == "user"
+
+
+def test_get_supported_openai_params_claude_model():
+    """Test that Claude models support thinking and reasoning parameters."""
+    config = GithubCopilotConfig()
+    
+    # Test Claude model supports thinking and reasoning_effort parameters
+    supported_params = config.get_supported_openai_params("claude-sonnet-4")
+    assert "thinking" in supported_params
+    assert "reasoning_effort" in supported_params
+    
+    # Test Claude model with different naming
+    supported_params_claude = config.get_supported_openai_params("claude-3.5-sonnet")
+    assert "thinking" in supported_params_claude
+    assert "reasoning_effort" in supported_params_claude
+    
+    # Test non-Claude model doesn't include thinking/reasoning parameters
+    supported_params_gpt = config.get_supported_openai_params("gpt-4o")
+    assert "thinking" not in supported_params_gpt
+    assert "reasoning_effort" not in supported_params_gpt
+    
+    # Test with other non-Claude models
+    supported_params_o3 = config.get_supported_openai_params("o3-mini")
+    assert "thinking" not in supported_params_o3
+    assert "reasoning_effort" not in supported_params_o3
+
+
+def test_get_supported_openai_params_case_insensitive():
+    """Test that Claude model detection is case-insensitive."""
+    config = GithubCopilotConfig()
+    
+    # Test uppercase
+    supported_params_upper = config.get_supported_openai_params("CLAUDE-SONNET-4")
+    assert "thinking" in supported_params_upper
+    assert "reasoning_effort" in supported_params_upper
+    
+    # Test mixed case
+    supported_params_mixed = config.get_supported_openai_params("Claude-3.5-Sonnet")
+    assert "thinking" in supported_params_mixed
+    assert "reasoning_effort" in supported_params_mixed