fix(openai): take the early Responses route decision on the request minus additional_drop_params

Filter the keys named in additional_drop_params out of the top level and extra_body before the hoisted
bridge check so a dropped reasoning_effort cannot move a chat-only custom endpoint onto /responses

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

litellm/main.py

@@ -1315,6 +1315,7 @@ from litellm.responses.bridge_check import (  # noqa: E402  # re-export at the o
     _resolve_openai_api_base as _resolve_openai_api_base,  # pyright: ignore[reportPrivateUsage]  # noqa: PLC0414  # re-export of moved helper
 )
 from litellm.responses.bridge_check import (
+    bridge_check_request_params,
     bridge_reasoning_effort,
     keep_registered_mode,
     str_keyed_mapping,
@@ -6045,13 +6046,16 @@ def completion(
         if dynamic_api_key is not None:
             api_key = dynamic_api_key
         if responses_api_model_info.get("mode") != "responses":
+            route_request_params: Final = bridge_check_request_params(routing_kwargs)
             responses_api_model_info, model = responses_api_bridge_check(
                 model=model,
                 custom_llm_provider=custom_llm_provider,
                 web_search_options=web_search_options,
                 tools=tools,
-                reasoning_effort=bridge_reasoning_effort(resolved_reasoning_effort, routing_kwargs.get("extra_body")),
-                reasoning_summary=peek_reasoning_summary_aliases(routing_kwargs),
+                reasoning_effort=bridge_reasoning_effort(
+                    resolved_reasoning_effort, route_request_params.get("extra_body")
+                ),
+                reasoning_summary=peek_reasoning_summary_aliases(route_request_params),
                 api_base=api_base,
                 deployment_model_info=deployment_model_info,
             )

litellm/responses/bridge_check.py

@@ -102,6 +102,24 @@ def str_keyed_mapping(value: object) -> Mapping[str, object] | None:
     )
 
 
+def bridge_check_request_params(request_params: Mapping[str, object]) -> Mapping[str, object]:
+    """The request as ``get_optional_params`` will hand it to the provider: every key named in
+    ``additional_drop_params`` removed at the top level and inside ``extra_body``, so the Responses route
+    decision taken before that call reads the same effort and summary alias the parsed params will carry."""
+    raw_dropped: Final = request_params.get("additional_drop_params")
+    dropped_params: Final = (
+        cast(Sequence[object], raw_dropped)  # cast-ok: isinstance only narrows to Sequence[Unknown]
+        if isinstance(raw_dropped, Sequence) and not isinstance(raw_dropped, str)
+        else ()
+    )
+    dropped: Final = frozenset(param for param in dropped_params if isinstance(param, str))
+    kept: Final = {key: value for key, value in request_params.items() if key not in dropped}
+    extra_body: Final = str_keyed_mapping(kept.get("extra_body"))
+    if extra_body is None:
+        return kept
+    return {**kept, "extra_body": {key: value for key, value in extra_body.items() if key not in dropped}}
+
+
 def bridge_reasoning_effort(
     reasoning_effort: str | Mapping[str, object] | None, extra_body: object
 ) -> str | Mapping[str, object] | None:

tests/integration/translation/chat_completions/params/test_chat_completions_params_openai_responses_web_search.py

@@ -5,6 +5,7 @@ import pytest
 from integration._support.client import Gateway
 from integration._support.provider import SharedProvider
 from integration.translation.case import TranslationTestCase
+from integration.translation.chat_completions.bases.openai import GPT_5_6_SOL_TEST_CASE as GPT_5_6_SOL_CHAT_TEST_CASE
 from integration.translation.chat_completions.bases.openai_responses import GPT_5_6_SOL_TEST_CASE
 from integration.translation.runner import assert_translation
 
@@ -78,10 +79,47 @@ GPT_5_6_SOL_LATE_BRIDGE_WEB_SEARCH_TEST_CASE: Final = replace(
     expected_litellm_response={**GPT_5_6_SOL_TEST_CASE.expected_litellm_response, "model": "openai/gpt-5.6-sol"},
 )
 
+# The rig's deployment has a custom api_base, which the bridge treats as a chat-only endpoint unless the
+# request names an effort. An effort the caller drops through additional_drop_params must not pick the
+# Responses route, so this request stays on /chat/completions exactly as before the early route decision
+GPT_5_6_SOL_DROPPED_EFFORT_STAYS_ON_CHAT_TEST_CASE: Final = replace(
+    GPT_5_6_SOL_CHAT_TEST_CASE,
+    scenario="dropped_extra_body_effort_stays_on_chat",
+    litellm_request={
+        **GPT_5_6_SOL_CHAT_TEST_CASE.litellm_request,
+        "extra_body": {"reasoning_effort": "low"},
+        "additional_drop_params": ["reasoning_effort"],
+        "tools": [
+            {
+                "type": "function",
+                "function": {
+                    "name": "get_weather",
+                    "description": "Get weather",
+                    "parameters": {"type": "object", "properties": {"city": {"type": "string"}}, "required": ["city"]},
+                },
+            }
+        ],
+    },
+    expected_provider_request={
+        **GPT_5_6_SOL_CHAT_TEST_CASE.expected_provider_request,
+        "tools": [
+            {
+                "type": "function",
+                "function": {
+                    "name": "get_weather",
+                    "description": "Get weather",
+                    "parameters": {"type": "object", "properties": {"city": {"type": "string"}}, "required": ["city"]},
+                },
+            }
+        ],
+    },
+)
+
 CASES: Final = (
     GPT_5_6_SOL_WEB_SEARCH_TEST_CASE,
     GPT_5_6_SOL_WEB_SEARCH_USER_LOCATION_TEST_CASE,
     GPT_5_6_SOL_LATE_BRIDGE_WEB_SEARCH_TEST_CASE,
+    GPT_5_6_SOL_DROPPED_EFFORT_STAYS_ON_CHAT_TEST_CASE,
 )
 
 

tests/unit/responses/test_bridge_check.py

@@ -0,0 +1,35 @@
+from litellm.responses.bridge_check import bridge_check_request_params
+
+
+def test_a_dropped_effort_inside_extra_body_is_not_read_by_the_route_decision():
+    request = {
+        "extra_body": {"reasoning_effort": "low", "reasoningSummary": "auto"},
+        "additional_drop_params": ["reasoning_effort"],
+        "tools": [{"type": "function", "function": {"name": "get_weather"}}],
+    }
+
+    params = bridge_check_request_params(request)
+
+    assert params["extra_body"] == {"reasoningSummary": "auto"}, params
+    assert params["tools"] is request["tools"]
+
+
+def test_a_dropped_top_level_alias_is_removed_too():
+    params = bridge_check_request_params({"reasoningSummary": "auto", "additional_drop_params": ["reasoningSummary"]})
+
+    assert "reasoningSummary" not in params, params
+
+
+def test_a_request_without_drops_is_returned_whole():
+    request = {"extra_body": {"reasoning_effort": "low"}, "tools": []}
+
+    params = bridge_check_request_params(request)
+
+    assert params == request
+    assert params["extra_body"] == {"reasoning_effort": "low"}
+
+
+def test_a_non_list_additional_drop_params_drops_nothing():
+    request = {"extra_body": {"reasoning_effort": "low"}, "additional_drop_params": "reasoning_effort"}
+
+    assert bridge_check_request_params(request)["extra_body"] == {"reasoning_effort": "low"}