From 6f8dc33acf2eee72df85b92e214568f1e60b70cb Mon Sep 17 00:00:00 2001
From: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Date: Tue, 14 Jul 2026 07:08:54 +0000
Subject: [PATCH] fix(router): serialize non-chat latency as seconds

---
 litellm/router_strategy/lowest_latency.py     | 24 +++++-------
 .../router_strategy/test_lowest_latency.py    | 37 +++++++++++++++++++
 2 files changed, 46 insertions(+), 15 deletions(-)
 create mode 100644 tests/test_litellm/router_strategy/test_lowest_latency.py

diff --git a/litellm/router_strategy/lowest_latency.py b/litellm/router_strategy/lowest_latency.py
index 23476fe7dcc..e21667ba9be 100644
--- a/litellm/router_strategy/lowest_latency.py
+++ b/litellm/router_strategy/lowest_latency.py
@@ -79,7 +79,10 @@ class LowestLatencyLoggingHandler(CustomLogger):
                     # only log ttft for streaming request
                     time_to_first_token_response_time = kwargs.get("completion_start_time", end_time) - start_time
 
-                final_value: Union[float, timedelta] = response_ms
+                response_seconds = (
+                    response_ms.total_seconds() if isinstance(response_ms, timedelta) else float(response_ms)
+                )
+                final_value = response_seconds
                 time_to_first_token: Optional[float] = None
                 total_tokens = 0
 
@@ -89,12 +92,6 @@ class LowestLatencyLoggingHandler(CustomLogger):
                         completion_tokens = _usage.completion_tokens
                         total_tokens = _usage.total_tokens
 
-                        # Handle both timedelta and float response times
-                        if isinstance(response_ms, timedelta):
-                            response_seconds = response_ms.total_seconds()
-                        else:
-                            response_seconds = response_ms
-
                         final_value = safe_divide_seconds(response_seconds, completion_tokens)
                         if final_value is not None:
                             final_value = float(final_value)
@@ -267,7 +264,10 @@ class LowestLatencyLoggingHandler(CustomLogger):
                     # only log ttft for streaming request
                     time_to_first_token_response_time = kwargs.get("completion_start_time", end_time) - start_time
 
-                final_value: Union[float, timedelta] = response_ms
+                response_seconds = (
+                    response_ms.total_seconds() if isinstance(response_ms, timedelta) else float(response_ms)
+                )
+                final_value = response_seconds
                 total_tokens = 0
                 time_to_first_token: Optional[float] = None
 
@@ -277,17 +277,11 @@ class LowestLatencyLoggingHandler(CustomLogger):
                         completion_tokens = _usage.completion_tokens
                         total_tokens = _usage.total_tokens
 
-                        # Handle both timedelta and float response times
-                        if isinstance(response_ms, timedelta):
-                            response_seconds = response_ms.total_seconds()
-                        else:
-                            response_seconds = response_ms
-
                         final_value = safe_divide_seconds(response_seconds, completion_tokens)
                         if final_value is not None:
                             final_value = float(final_value)
                         else:
-                            final_value = response_ms
+                            final_value = response_seconds
 
                         if time_to_first_token_response_time is not None:
                             if isinstance(time_to_first_token_response_time, timedelta):
diff --git a/tests/test_litellm/router_strategy/test_lowest_latency.py b/tests/test_litellm/router_strategy/test_lowest_latency.py
new file mode 100644
index 00000000000..2e2e0f7a56d
--- /dev/null
+++ b/tests/test_litellm/router_strategy/test_lowest_latency.py
@@ -0,0 +1,37 @@
+import json
+from datetime import datetime, timedelta
+
+import pytest
+
+import litellm
+from litellm.caching.caching import DualCache
+from litellm.router_strategy.lowest_latency import LowestLatencyLoggingHandler
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("sync_mode", [True, False])
+async def test_non_chat_latency_is_json_serializable(sync_mode: bool) -> None:
+    cache = DualCache()
+    handler = LowestLatencyLoggingHandler(router_cache=cache)
+    model_group = "embedding-group"
+    deployment_id = "embedding-deployment"
+    kwargs = {
+        "litellm_params": {
+            "metadata": {"model_group": model_group},
+            "model_info": {"id": deployment_id},
+        }
+    }
+    start_time = datetime.now()
+    end_time = start_time + timedelta(seconds=1.25)
+    response = litellm.EmbeddingResponse()
+
+    if sync_mode:
+        handler.log_success_event(kwargs, response, start_time, end_time)
+    else:
+        await handler.async_log_success_event(kwargs, response, start_time, end_time)
+
+    cached_value = cache.get_cache(key=f"{model_group}_map")
+    latency = cached_value[deployment_id]["latency"][0]
+    assert latency == 1.25
+    assert isinstance(latency, float)
+    json.dumps(cached_value)