fix(proxy): map stripped batch body.model to proxy alias for auth (#29264)

* fix(proxy): map stripped batch body.model to proxy alias for auth

replace_model_in_jsonl rewrites JSONL body.model to the provider id before
upload; batch file access checks must resolve that id back to model_name
so keys granted the proxy alias are not rejected with 403.

Co-authored-by: Cursor <cursoragent@cursor.com>

* fix(proxy): surface resolved proxy alias in batch file 403 detail

---------

Co-authored-by: Cursor <cursoragent@cursor.com>
Co-authored-by: mateo-berri <277851410+mateo-berri@users.noreply.github.com>

litellm/proxy/hooks/batch_rate_limiter.py

@@ -308,9 +308,15 @@ class _PROXY_BatchRateLimiter(CustomLogger):
 
         llm_model_list = llm_router.model_list if llm_router is not None else None
         for model in models:
+            # body.model may be the provider id after replace_model_in_jsonl; map to proxy model_name for auth.
+            model_to_check = model
+            if llm_router is not None:
+                proxy_model_name = llm_router.resolve_model_name_from_model_id(model)
+                if proxy_model_name is not None:
+                    model_to_check = proxy_model_name
             try:
                 await can_key_call_model(
-                    model=model,
+                    model=model_to_check,
                     llm_model_list=llm_model_list,
                     valid_token=user_api_key_dict,
                     llm_router=llm_router,
@@ -326,7 +332,7 @@ class _PROXY_BatchRateLimiter(CustomLogger):
                     detail={
                         "error": (
                             "Batch input file references a model the caller is "
-                            f"not authorized to use: model={model}, reason={str(e)}"
+                            f"not authorized to use: model={model_to_check}, reason={str(e)}"
                         )
                     },
                 )

tests/test_litellm/proxy/hooks/test_batch_file_validation.py

@@ -14,7 +14,6 @@ from fastapi import HTTPException
 
 from litellm.proxy._types import LitellmUserRoles, UserAPIKeyAuth
 
-
 # ---------------------------------------------------------------------------
 # Token counter — covers all three batch payload shapes
 # ---------------------------------------------------------------------------
@@ -260,6 +259,47 @@ async def test_pre_call_allows_authorized_model_in_batch_file():
         )
 
 
+@pytest.mark.asyncio
+async def test_pre_call_allows_stripped_provider_model_when_key_has_proxy_alias():
+    """After replace_model_in_jsonl, body.model is the provider id (e.g. gpt-5.5).
+    Auth must check the proxy model_name the key was granted, not the stripped id."""
+    from litellm.proxy.hooks.batch_rate_limiter import _PROXY_BatchRateLimiter
+
+    rate_limiter = _PROXY_BatchRateLimiter(
+        internal_usage_cache=MagicMock(),
+        parallel_request_limiter=MagicMock(),
+    )
+    proxy_alias = "openai/openai/gpt-5.5-batch"
+    file_dict = [
+        {"body": {"model": "gpt-5.5", "messages": [{"role": "user", "content": "x"}]}}
+    ]
+    user = UserAPIKeyAuth(
+        api_key="sk-ok",
+        user_id="alice",
+        models=[proxy_alias],
+        user_role=LitellmUserRoles.INTERNAL_USER.value,
+    )
+    mock_router = MagicMock()
+    mock_router.model_list = []
+    mock_router.resolve_model_name_from_model_id.return_value = proxy_alias
+    can_key_call_model = AsyncMock(return_value=True)
+
+    with (
+        patch(
+            "litellm.proxy.auth.auth_checks.can_key_call_model",
+            new=can_key_call_model,
+        ),
+        patch("litellm.proxy.proxy_server.llm_router", mock_router),
+    ):
+        await rate_limiter._enforce_batch_file_model_access(
+            user_api_key_dict=user,
+            file_content_as_dict=file_dict,
+        )
+
+    can_key_call_model.assert_awaited_once()
+    assert can_key_call_model.await_args.kwargs["model"] == proxy_alias
+
+
 @pytest.mark.asyncio
 async def test_pre_call_skips_check_when_no_models_present():
     """Files without any `body.model` (corrupt or empty) must not 500;