Add native Responses API support for litellm_proxy provider (#15347)

* Initial plan

* Add native Responses API support for litellm_proxy provider

Co-authored-by: ishaan-jaff <[email protected]>

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: ishaan-jaff <[email protected]>

Author: Copilot

litellm/__init__.py

@@ -1190,6 +1190,9 @@ def add_known_models():
 from .llms.azure.responses.o_series_transformation import (
     AzureOpenAIOSeriesResponsesAPIConfig,
 )
+from .llms.litellm_proxy.responses.transformation import (
+    LiteLLMProxyResponsesAPIConfig,
+)
 from .llms.openai.chat.o_series_transformation import (
     OpenAIOSeriesConfig as OpenAIO1Config,  # maintain backwards compatibility
     OpenAIOSeriesConfig,

litellm/llms/litellm_proxy/responses/transformation.py

@@ -0,0 +1,48 @@
+"""
+Responses API transformation for LiteLLM Proxy provider.
+
+LiteLLM Proxy supports the OpenAI Responses API natively when the underlying model supports it.
+This config enables pass-through behavior to the proxy's /v1/responses endpoint.
+"""
+
+from typing import Optional
+
+from litellm.llms.openai.responses.transformation import OpenAIResponsesAPIConfig
+from litellm.secret_managers.main import get_secret_str
+from litellm.types.utils import LlmProviders
+
+
+class LiteLLMProxyResponsesAPIConfig(OpenAIResponsesAPIConfig):
+    """
+    Configuration for LiteLLM Proxy Responses API support.
+    
+    Extends OpenAI's config since the proxy follows OpenAI's API spec,
+    but uses LITELLM_PROXY_API_BASE for the base URL.
+    """
+
+    @property
+    def custom_llm_provider(self) -> LlmProviders:
+        return LlmProviders.LITELLM_PROXY
+
+    def get_complete_url(
+        self,
+        api_base: Optional[str],
+        litellm_params: dict,
+    ) -> str:
+        """
+        Get the endpoint for LiteLLM Proxy responses API.
+        
+        Uses LITELLM_PROXY_API_BASE environment variable if api_base is not provided.
+        """
+        api_base = api_base or get_secret_str("LITELLM_PROXY_API_BASE")
+        
+        if api_base is None:
+            raise ValueError(
+                "api_base not set for LiteLLM Proxy responses API. "
+                "Set via api_base parameter or LITELLM_PROXY_API_BASE environment variable"
+            )
+
+        # Remove trailing slashes
+        api_base = api_base.rstrip("/")
+
+        return f"{api_base}/responses"

litellm/utils.py

@@ -7305,6 +7305,8 @@ def get_provider_responses_api_config(
                 return litellm.AzureOpenAIOSeriesResponsesAPIConfig()
             else:
                 return litellm.AzureOpenAIResponsesAPIConfig()
+        elif litellm.LlmProviders.LITELLM_PROXY == provider:
+            return litellm.LiteLLMProxyResponsesAPIConfig()
         return None
 
     @staticmethod

tests/local_testing/test_config.py

@@ -401,3 +401,24 @@ def test_provider_config_manager_bedrock_converse_like():
 #             model="gpt-3.5-turbo", provider=LlmProviders(provider)
 #         )
 #         _check_provider_config(config, provider)
+
+
+def test_litellm_proxy_responses_api_config():
+    """Test that litellm_proxy provider returns correct Responses API config"""
+    from litellm.llms.litellm_proxy.responses.transformation import (
+        LiteLLMProxyResponsesAPIConfig,
+    )
+
+    config = ProviderConfigManager.get_provider_responses_api_config(
+        model="litellm_proxy/gpt-4",
+        provider=LlmProviders.LITELLM_PROXY,
+    )
+    print(f"config: {config}")
+    assert config is not None, "Config should not be None for litellm_proxy provider"
+    assert isinstance(
+        config, LiteLLMProxyResponsesAPIConfig
+    ), f"Expected LiteLLMProxyResponsesAPIConfig, got {type(config)}"
+    assert (
+        config.custom_llm_provider == LlmProviders.LITELLM_PROXY
+    ), "custom_llm_provider should be LITELLM_PROXY"
+

tests/test_litellm_proxy_responses_config.py

@@ -0,0 +1,84 @@
+"""
+Unit test for LiteLLM Proxy Responses API configuration.
+"""
+
+import pytest
+
+from litellm.types.utils import LlmProviders
+from litellm.utils import ProviderConfigManager
+
+
+def test_litellm_proxy_responses_api_config():
+    """Test that litellm_proxy provider returns correct Responses API config"""
+    from litellm.llms.litellm_proxy.responses.transformation import (
+        LiteLLMProxyResponsesAPIConfig,
+    )
+
+    config = ProviderConfigManager.get_provider_responses_api_config(
+        model="litellm_proxy/gpt-4",
+        provider=LlmProviders.LITELLM_PROXY,
+    )
+    print(f"config: {config}")
+    assert config is not None, "Config should not be None for litellm_proxy provider"
+    assert isinstance(
+        config, LiteLLMProxyResponsesAPIConfig
+    ), f"Expected LiteLLMProxyResponsesAPIConfig, got {type(config)}"
+    assert (
+        config.custom_llm_provider == LlmProviders.LITELLM_PROXY
+    ), "custom_llm_provider should be LITELLM_PROXY"
+
+
+def test_litellm_proxy_responses_api_config_get_complete_url():
+    """Test that get_complete_url works correctly"""
+    import os
+    from litellm.llms.litellm_proxy.responses.transformation import (
+        LiteLLMProxyResponsesAPIConfig,
+    )
+
+    config = LiteLLMProxyResponsesAPIConfig()
+
+    # Test with explicit api_base
+    url = config.get_complete_url(
+        api_base="https://my-proxy.example.com",
+        litellm_params={},
+    )
+    assert url == "https://my-proxy.example.com/responses"
+
+    # Test with trailing slash
+    url = config.get_complete_url(
+        api_base="https://my-proxy.example.com/",
+        litellm_params={},
+    )
+    assert url == "https://my-proxy.example.com/responses"
+
+    # Test that it raises error when api_base is None and env var is not set
+    if "LITELLM_PROXY_API_BASE" in os.environ:
+        del os.environ["LITELLM_PROXY_API_BASE"]
+    
+    with pytest.raises(ValueError, match="api_base not set"):
+        config.get_complete_url(api_base=None, litellm_params={})
+
+
+def test_litellm_proxy_responses_api_config_inherits_from_openai():
+    """Test that LiteLLMProxyResponsesAPIConfig extends OpenAI config properly"""
+    from litellm.llms.litellm_proxy.responses.transformation import (
+        LiteLLMProxyResponsesAPIConfig,
+    )
+    from litellm.llms.openai.responses.transformation import (
+        OpenAIResponsesAPIConfig,
+    )
+
+    config = LiteLLMProxyResponsesAPIConfig()
+    
+    # Should inherit from OpenAI config
+    assert isinstance(config, OpenAIResponsesAPIConfig)
+    
+    # Should have the correct provider set
+    assert config.custom_llm_provider == LlmProviders.LITELLM_PROXY
+
+
+if __name__ == "__main__":
+    test_litellm_proxy_responses_api_config()
+    test_litellm_proxy_responses_api_config_get_complete_url()
+    test_litellm_proxy_responses_api_config_inherits_from_openai()
+    print("All tests passed!")