From 3458e4aae1081d6d154fd5df8bd8ec3570455b14 Mon Sep 17 00:00:00 2001
From: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Date: Sun, 25 Oct 2026 17:27:57 +0000
Subject: [PATCH] fix(router): validate text batch without cast

---
 litellm/router.py | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/litellm/router.py b/litellm/router.py
index 1fc7ee3cb15..6c5d47467d0 100644
--- a/litellm/router.py
+++ b/litellm/router.py
@@ -610,6 +610,7 @@ _SESSION_ADAPTER: Final = TypeAdapter(Mapping[str, object])
 _MODEL_INFO_ADAPTER: Final = TypeAdapter(Mapping[str, object])
 _LITELLM_PARAMS_ADAPTER: Final = TypeAdapter(Mapping[str, object])
 _SILENT_MODEL_ADAPTER: Final = TypeAdapter(str | list[str])
+_TEXT_INPUT_BATCH_ADAPTER: Final = TypeAdapter(list[str])
 _RESOLVED_RETRY_POLICY_ADAPTER: Final = TypeAdapter(RetryPolicy | None)
 _ROUTING_KWARGS_ADAPTER: Final[TypeAdapter[Mapping[str, object] | None]] = TypeAdapter(Mapping[str, object] | None)
 _FALLBACK_HOP_ADAPTER: Final = TypeAdapter(Mapping[str, object])
@@ -14348,12 +14349,13 @@ class Router:
         from litellm.litellm_core_utils.prompt_templates.factory import resolve_structured_messages
 
         input_data: Final = request_kwargs.get("input")
-        if (
-            not messages
-            and isinstance(input_data, list)
-            and all(isinstance(item, str) for item in input_data)
-        ):
-            return False
+        if not messages:
+            try:
+                _TEXT_INPUT_BATCH_ADAPTER.validate_python(input_data, strict=True)
+            except ValidationError:
+                pass
+            else:
+                return False
 
         structured: Final = resolve_structured_messages(
             messages=cast(list[dict[str, object]] | None, messages),  # cast-ok: chat messages are plain dicts