fix(responses): update local_vars with detected provider (#19782) (#19798)

When using the responses API with provider-specific params (aws_*, vertex_*)
without explicitly passing custom_llm_provider, the code crashed with:
AttributeError: 'NoneType' object has no attribute 'startswith'

Root cause: local_vars was captured via locals() before get_llm_provider()
detected the provider from the model string (e.g., "bedrock/..."), so
custom_llm_provider remained None when processing provider-specific params.

Fix: Update local_vars["custom_llm_provider"] after get_llm_provider() call
so the detected provider is available for param processing.

Affected provider-specific params:
- aws_* (aws_region_name, aws_access_key_id, etc.) for Bedrock/SageMaker
- vertex_* (vertex_project, vertex_location, etc.) for Vertex AI

litellm/responses/main.py

@@ -434,6 +434,8 @@ async def aresponses(
             _, custom_llm_provider, _, _ = litellm.get_llm_provider(
                 model=model, api_base=local_vars.get("base_url", None)
             )
+            # Update local_vars with detected provider (fixes #19782)
+            local_vars["custom_llm_provider"] = custom_llm_provider
 
         func = partial(
             responses,
@@ -583,6 +585,9 @@ def responses(
             api_key=litellm_params.api_key,
         )
 
+        # Update local_vars with detected provider (fixes #19782)
+        local_vars["custom_llm_provider"] = custom_llm_provider
+
         # Use dynamic credentials from get_llm_provider (e.g., when use_litellm_proxy=True)
         if dynamic_api_key is not None:
             litellm_params.api_key = dynamic_api_key
@@ -1411,6 +1416,8 @@ async def acompact_responses(
             _, custom_llm_provider, _, _ = litellm.get_llm_provider(
                 model=model, api_base=local_vars.get("base_url", None)
             )
+            # Update local_vars with detected provider (fixes #19782)
+            local_vars["custom_llm_provider"] = custom_llm_provider
 
         func = partial(
             compact_responses,
@@ -1498,6 +1505,9 @@ def compact_responses(
             api_key=litellm_params.api_key,
         )
 
+        # Update local_vars with detected provider (fixes #19782)
+        local_vars["custom_llm_provider"] = custom_llm_provider
+
         # Use dynamic credentials from get_llm_provider (e.g., when use_litellm_proxy=True)
         if dynamic_api_key is not None:
             litellm_params.api_key = dynamic_api_key

tests/test_litellm/responses/test_responses_utils.py

@@ -309,3 +309,46 @@ class TestResponseAPILoggingUtils:
         assert result.completion_tokens_details.reasoning_tokens == 30
         assert result.completion_tokens_details.image_tokens == 100
         assert result.completion_tokens_details.text_tokens == 70
+
+
+class TestResponsesAPIProviderSpecificParams:
+    """
+    Tests for fix #19782: provider-specific params (aws_*, vertex_*) should work
+    without explicitly passing custom_llm_provider.
+    """
+
+    def test_provider_specific_params_no_crash_with_bedrock(self):
+        """Test that processing aws_* params with bedrock provider doesn't crash."""
+        params = {
+            "temperature": 0.7,
+            "custom_llm_provider": "bedrock",
+            "kwargs": {"aws_region_name": "eu-central-1"},
+        }
+
+        # Should not raise any exception
+        result = ResponsesAPIRequestUtils.get_requested_response_api_optional_param(params)
+        assert "temperature" in result
+
+    def test_provider_specific_params_no_crash_with_openai(self):
+        """Test that processing aws_* params with openai provider doesn't crash."""
+        params = {
+            "temperature": 0.7,
+            "custom_llm_provider": "openai",
+            "kwargs": {"aws_region_name": "eu-central-1"},
+        }
+
+        # Should not raise any exception
+        result = ResponsesAPIRequestUtils.get_requested_response_api_optional_param(params)
+        assert "temperature" in result
+
+    def test_provider_specific_params_no_crash_with_vertex_ai(self):
+        """Test that processing vertex_* params with vertex_ai provider doesn't crash."""
+        params = {
+            "temperature": 0.7,
+            "custom_llm_provider": "vertex_ai",
+            "kwargs": {"vertex_project": "my-project"},
+        }
+
+        # Should not raise any exception
+        result = ResponsesAPIRequestUtils.get_requested_response_api_optional_param(params)
+        assert "temperature" in result