diff --git a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
index db2e7de37c3..de058add0c9 100644
--- a/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
+++ b/litellm/proxy/_experimental/mcp_server/mcp_server_manager.py
@@ -6045,11 +6045,12 @@ class MCPServerManager:
         if proxy_logging_obj is None:
             return hook_result
 
-        inbound_authorization: Final = _raw_header_value(raw_headers, "authorization") or ""
+        normalized_raw: Final = {k.lower(): v for k, v in (raw_headers or {}).items()}
+        inbound_authorization: Final = normalized_raw.get("authorization", "")
         incoming_bearer_token: Final = (
             inbound_authorization[len("bearer ") :] if inbound_authorization.lower().startswith("bearer ") else None
         )
-        incoming_subject_token: Final = self._caller_sign_in_subject_token(None, raw_headers)
+        incoming_subject_token: Final = self._caller_sign_in_subject_token(None, normalized_raw)
 
         pre_hook_kwargs: Final = {
             "guardrail_context": guardrail_context,
diff --git a/tests/unit/proxy/_experimental/mcp_server/test_mcp_server_manager.py b/tests/unit/proxy/_experimental/mcp_server/test_mcp_server_manager.py
index fc16bb17506..86ced491b3f 100644
--- a/tests/unit/proxy/_experimental/mcp_server/test_mcp_server_manager.py
+++ b/tests/unit/proxy/_experimental/mcp_server/test_mcp_server_manager.py
@@ -6992,6 +6992,20 @@ class TestMCPServerManager:
                 " eyJ.x.y",
                 id="bearer-credential-is-taken-verbatim-after-one-space",
             ),
+            pytest.param(
+                {"authorization": "Bearer sk-request-key", "Authorization": "Bearer eyJ.caller.jws"},
+                "sk-request-key",
+                "eyJ.caller.jws",
+                "eyJ.caller.jws",
+                id="responses-bridge-tool-authorization-overrides-the-request-key",
+            ),
+            pytest.param(
+                {"Authorization": "Bearer eyJ.caller.jws", "authorization": "Bearer sk-request-key"},
+                "sk-request-key",
+                "sk-request-key",
+                None,
+                id="last-duplicate-case-authorization-wins",
+            ),
         ],
     )
     async def test_pre_call_tool_check_separates_raw_bearer_from_subject(