diff --git a/litellm/utils.py b/litellm/utils.py
index ca878721197..d71a6917173 100644
--- a/litellm/utils.py
+++ b/litellm/utils.py
@@ -2538,6 +2538,12 @@ def _supports_factory(model: str, custom_llm_provider: Optional[str], key: str)
             model=model, custom_llm_provider=custom_llm_provider
         )
 
+        # Strip responses/ prefix so capability lookups resolve to the
+        # base model entry in the cost map (e.g. "gpt-5.4" not
+        # "responses/gpt-5.4").  See #23423.
+        if model.startswith("responses/"):
+            model = model[len("responses/"):]
+
         model_info = _get_model_info_helper(
             model=model, custom_llm_provider=custom_llm_provider
         )
diff --git a/tests/test_litellm/test_utils.py b/tests/test_litellm/test_utils.py
index 64488e2fb6a..826ae1917cd 100644
--- a/tests/test_litellm/test_utils.py
+++ b/tests/test_litellm/test_utils.py
@@ -998,6 +998,10 @@ def test_supports_tool_choice_simple_tests():
 
     assert litellm.utils.supports_tool_choice(model="perplexity/sonar") is False
 
+    # Responses API prefix must resolve to base model. See #23423.
+    assert litellm.utils.supports_tool_choice(model="openai/responses/gpt-5.4") is True
+    assert litellm.utils.supports_tool_choice(model="responses/gpt-5.4", custom_llm_provider="openai") is True
+
 
 def test_check_provider_match():
     """