diff --git a/litellm/router_strategy/complexity_router/complexity_router.py b/litellm/router_strategy/complexity_router/complexity_router.py
index f0f5ce331a3..bb951e7fbb8 100644
--- a/litellm/router_strategy/complexity_router/complexity_router.py
+++ b/litellm/router_strategy/complexity_router/complexity_router.py
@@ -1747,8 +1747,8 @@ class ComplexityRouter(CustomLogger):
         user_identifier = self._get_user_identifier_from_request_kwargs(request_kwargs)
         model_group = model or self.model_name or request_kwargs.get("model") or ""
 
-        payload = f"{user_identifier}:{model_group}:{first_system_msg}:{first_user_msg}"
-        return hashlib.sha256(payload.encode("utf-8")).hexdigest()
+        payload = f"litellm-session-key:{user_identifier}:{model_group}:{first_system_msg}:{first_user_msg}"
+        return hashlib.sha256(payload.encode("utf-8", errors="replace")).hexdigest()
 
     def _resolve_session_id(
         self,
@@ -1776,9 +1776,10 @@ class ComplexityRouter(CustomLogger):
             )
 
         if derived_key is not None:
+            sanitized_key = derived_key.replace("\r", "").replace("\n", "")[:32]
             verbose_router_logger.info(
                 "ComplexityRouter: resolved fallback session key '%s' using strategy '%s'",
-                derived_key,
+                sanitized_key,
                 fallback,
             )
             metadata_key = "litellm_metadata" if "litellm_metadata" in request_kwargs else "metadata"
diff --git a/tests/test_litellm/router_strategy/test_session_key_fallback.py b/tests/test_litellm/router_strategy/test_session_key_fallback.py
index 1bcbdd5b09b..5e336e86a2a 100644
--- a/tests/test_litellm/router_strategy/test_session_key_fallback.py
+++ b/tests/test_litellm/router_strategy/test_session_key_fallback.py
@@ -240,7 +240,7 @@ class TestSessionKeyFallback:
         # user_api_key_hash : model_group : first_system_msg : first_user_msg
         system_text = "You are a mathematics tutor."
         user_text = "Let's think step by step and reason through this problem carefully."
-        expected_payload = f"user_hash_abc:test-router:{system_text}:{user_text}"
+        expected_payload = f"litellm-session-key:user_hash_abc:test-router:{system_text}:{user_text}"
         expected_hash = hashlib.sha256(expected_payload.encode("utf-8")).hexdigest()
 
         derived_id = router._resolve_session_id(