diff --git a/litellm/utils.py b/litellm/utils.py
index 14ee35e571e..a6108a15bb3 100644
--- a/litellm/utils.py
+++ b/litellm/utils.py
@@ -5552,8 +5552,9 @@ def add_provider_specific_params_to_optional_params(
         # for openai, azure we should pass the extra/passed params within `extra_body` https://github.com/openai/openai-python/blob/ac33853ba10d13ac149b1fa3ca6dba7d613065c9/src/openai/resources/models.py#L46
         if _should_drop_param(k="extra_body", additional_drop_params=additional_drop_params) is False:
             extra_body: Final = dict(passed_params.pop("extra_body", None) or {})
+            withheld_params: Final = frozenset[str]() if custom_llm_provider == "litellm_proxy" else LITELLM_ONLY_PARAMS
             for k in passed_params:
-                if k not in openai_params and k not in LITELLM_ONLY_PARAMS and passed_params[k] is not None:
+                if k not in openai_params and k not in withheld_params and passed_params[k] is not None:
                     extra_body[k] = passed_params[k]
             if not isinstance(optional_params.get("extra_body"), dict):
                 optional_params["extra_body"] = {}
diff --git a/tests/unit/test_utils.py b/tests/unit/test_utils.py
index 44939ca7585..0be3ae05e97 100644
--- a/tests/unit/test_utils.py
+++ b/tests/unit/test_utils.py
@@ -10703,3 +10703,18 @@ def test_get_optional_params_keeps_a_tool_config_cache_point_out_of_the_openai_e
 
     assert optional_params["extra_body"] == {"kept": True}
     assert "cache_control_injection_points" not in optional_params
+
+
+def test_get_optional_params_forwards_a_tool_config_cache_point_to_a_downstream_litellm_proxy():
+    """A litellm_proxy deployment calls the downstream proxy through the OpenAI SDK, and that proxy
+    applies cache_control_injection_points itself, so the point must ride along in extra_body."""
+    point: Final = {"location": "tool_config", "control": {"type": "ephemeral"}}
+    optional_params: Final[dict[str, object]] = litellm.utils.get_optional_params(
+        model="claude-sonnet-4-5",
+        custom_llm_provider="litellm_proxy",
+        tools=[{"type": "function", "function": {"name": "get_weather", "parameters": {"type": "object"}}}],
+        cache_control_injection_points=[point],
+        extra_body={"kept": True},
+    )
+
+    assert optional_params["extra_body"] == {"kept": True, "cache_control_injection_points": [point]}