From 6fa72652fc161016ff99f5f1727d9197e12fd311 Mon Sep 17 00:00:00 2001
From: Yash Raj Pandey <yashpn62@gmail.com>
Date: Thu, 27 Aug 2026 11:25:42 -0400
Subject: [PATCH] test(router): pin numeric cost sorting in cost-based routing

A config can supply input_cost_per_token and output_cost_per_token as strings. Before the float cast, + concatenated them and sorted ordered the cost strings lexically, so the router silently picked the costlier deployment. A missing output cost mixed a string with a float and raised TypeError

Both tests fail when the float cast is reverted
---
 .../router_strategy/test_lowest_cost.py       | 56 +++++++++++++++++++
 1 file changed, 56 insertions(+)
 create mode 100644 tests/test_litellm/router_strategy/test_lowest_cost.py

diff --git a/tests/test_litellm/router_strategy/test_lowest_cost.py b/tests/test_litellm/router_strategy/test_lowest_cost.py
new file mode 100644
index 00000000000..0b238eef3dd
--- /dev/null
+++ b/tests/test_litellm/router_strategy/test_lowest_cost.py
@@ -0,0 +1,56 @@
+import pytest
+
+from litellm.caching.caching import DualCache
+from litellm.router_strategy.lowest_cost import LowestCostLoggingHandler
+
+
+@pytest.mark.asyncio
+async def test_string_costs_are_sorted_numerically():
+    handler = LowestCostLoggingHandler(router_cache=DualCache())
+    deployments = [
+        {
+            "model_name": "test-model-group",
+            "litellm_params": {
+                "model": "test/unknown-model",
+                "input_cost_per_token": "0.000009",
+                "output_cost_per_token": "0.000009",
+            },
+            "model_info": {"id": "cheap"},
+        },
+        {
+            "model_name": "test-model-group",
+            "litellm_params": {
+                "model": "test/unknown-model",
+                "input_cost_per_token": "0.000008",
+                "output_cost_per_token": "0.000012",
+            },
+            "model_info": {"id": "costly"},
+        },
+    ]
+
+    selected = await handler.async_get_available_deployments(
+        model_group="test-model-group", healthy_deployments=deployments
+    )
+
+    assert selected["model_info"]["id"] == "cheap"
+
+
+@pytest.mark.asyncio
+async def test_string_input_cost_with_default_output_cost_does_not_raise():
+    handler = LowestCostLoggingHandler(router_cache=DualCache())
+    deployments = [
+        {
+            "model_name": "test-model-group",
+            "litellm_params": {
+                "model": "test/unknown-model",
+                "input_cost_per_token": "0.000009",
+            },
+            "model_info": {"id": "mixed"},
+        }
+    ]
+
+    selected = await handler.async_get_available_deployments(
+        model_group="test-model-group", healthy_deployments=deployments
+    )
+
+    assert selected is not None