From a2f9963a1d38ddb8afad8b59b4d143fe6b278447 Mon Sep 17 00:00:00 2001
From: PRABHU KIRAN VANDRANKI <72809214+VANDRANKI@users.noreply.github.com>
Date: Fri, 22 May 2026 11:51:19 -0400
Subject: [PATCH] fix(router): call async_pre_routing_hook in non-async routing
 strategy fallback path

Fixes #26224: complexity_router and other auto-routers that rely on
async_pre_routing_hook to resolve router model names were silently
bypassed when the default (non-async) routing strategy was active.

The async_get_available_deployment function falls back to the sync
get_available_deployment for routing strategies that don't have an
async implementation. This fallback skipped async_pre_routing_hook
entirely, so the model name was never resolved from the router alias
(e.g. 'smart-router') to the actual downstream model (e.g.
'claude-sonnet-4-6'), causing downstream errors like 'unknown model
auto_router/complexity_router'.

Fix: call async_pre_routing_hook before get_available_deployment in
the sync fallback path so the model is properly resolved regardless
of routing strategy.
---
 litellm/router.py | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/litellm/router.py b/litellm/router.py
index 9185e437a3a..73ee37c243e 100644
--- a/litellm/router.py
+++ b/litellm/router.py
@@ -9317,6 +9317,20 @@ class Router:
             and self.routing_strategy != "latency-based-routing"
             and self.routing_strategy != "least-busy"
         ):  # prevent regressions for other routing strategies, that don't have async get available deployments implemented.
+            # Run async pre-routing hooks (e.g. complexity_router) so that router
+            # model names are resolved to the correct downstream model before
+            # deployment selection, even when a non-async routing strategy is used.
+            pre_routing_hook_response = await self.async_pre_routing_hook(
+                model=model,
+                request_kwargs=request_kwargs,
+                messages=messages,
+                input=input,
+                specific_deployment=specific_deployment,
+            )
+            if pre_routing_hook_response is not None:
+                model = pre_routing_hook_response.model
+                if pre_routing_hook_response.messages is not None:
+                    messages = pre_routing_hook_response.messages
             return self.get_available_deployment(
                 model=model,
                 messages=messages,