diff --git a/litellm/proxy/management_endpoints/key_management_endpoints.py b/litellm/proxy/management_endpoints/key_management_endpoints.py
index d4a0a35d9eb..d54eda45160 100644
--- a/litellm/proxy/management_endpoints/key_management_endpoints.py
+++ b/litellm/proxy/management_endpoints/key_management_endpoints.py
@@ -5104,9 +5104,14 @@ async def info_key_fn(
 
         # default to using Auth token if no key is passed in
         key = key or user_api_key_dict.api_key
-        hashed_key: str | None = key
-        if key is not None:
-            hashed_key = hash_token_if_needed(token=key)  # rebind-ok: pre-existing rebinding on a rename-only line
+        if not key:
+            raise ProxyException(
+                message="No key passed in. Pass ?key= or authenticate with a virtual key.",
+                type=ProxyErrorTypes.bad_request_error,
+                param="key",
+                code=status.HTTP_400_BAD_REQUEST,
+            )
+        hashed_key: str | None = hash_token_if_needed(token=key)
         live_key_info: Final = await _prisma_table(VerificationTokenRepository(prisma_client)).find_unique(
             where={"token": hashed_key},
             include={"litellm_budget_table": True},
diff --git a/tests/unit/proxy/management_endpoints/test_key_management_endpoints.py b/tests/unit/proxy/management_endpoints/test_key_management_endpoints.py
index 77dc6eddf51..f83d53ac2e5 100644
--- a/tests/unit/proxy/management_endpoints/test_key_management_endpoints.py
+++ b/tests/unit/proxy/management_endpoints/test_key_management_endpoints.py
@@ -6980,6 +6980,22 @@ async def test_info_key_fn_unknown_key_still_404s(monkeypatch):
     assert exc_info.value.code == "404"
 
 
+@pytest.mark.asyncio
+async def test_info_key_fn_no_key_returns_400_not_500(monkeypatch):
+    """#43571: when both ?key= and auth api_key are None, return a clean 400
+    instead of letting Prisma raise MissingRequiredValueError as a 500."""
+    from litellm.proxy.management_endpoints.key_management_endpoints import info_key_fn
+
+    mock_prisma_client = AsyncMock()
+    monkeypatch.setattr("litellm.proxy.proxy_server.prisma_client", mock_prisma_client)
+
+    auth = UserAPIKeyAuth(user_role=LitellmUserRoles.PROXY_ADMIN, api_key=None)
+    with pytest.raises(ProxyException) as exc_info:
+        await info_key_fn(key=None, user_api_key_dict=auth)
+    assert exc_info.value.code == "400"
+    mock_prisma_client.db.litellm_verificationtoken.find_unique.assert_not_called()
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize(
     ("blocked", "expires", "expected_status"),