diff --git a/litellm/responses/main.py b/litellm/responses/main.py
index 83c23a58500..b2c2493c812 100644
--- a/litellm/responses/main.py
+++ b/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
diff --git a/tests/test_litellm/responses/test_responses_utils.py b/tests/test_litellm/responses/test_responses_utils.py
index 3eb9c63e1be..8f7acb6c120 100644
--- a/tests/test_litellm/responses/test_responses_utils.py
+++ b/tests/test_litellm/responses/test_responses_utils.py
@@ -309,3 +309,46 @@ def test_transform_response_api_usage_mixed_details(self):
         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