From 4f0a780391b4482333ff127091f398278a366da9 Mon Sep 17 00:00:00 2001
From: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Date: Thu, 23 Apr 2026 17:30:56 -0700
Subject: [PATCH] test: regression test for completion_tokens_details on
 Responses API usage (#15377)

Adds a focused regression test asserting that
ResponseAPILoggingUtils._transform_response_api_usage_to_chat_usage()
populates Usage.completion_tokens_details.reasoning_tokens from
output_tokens_details.reasoning_tokens, matching what Chat Completions
produces.

The underlying fix already shipped on main (shared OpenAI Responses path
used by Azure Responses), so this locks in the behaviour to prevent
regressions on the Azure Responses API path reported in #15377.
---
 .../responses/test_responses_utils.py         | 32 +++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/tests/test_litellm/responses/test_responses_utils.py b/tests/test_litellm/responses/test_responses_utils.py
index 60b84f0e0a8..89788d40a00 100644
--- a/tests/test_litellm/responses/test_responses_utils.py
+++ b/tests/test_litellm/responses/test_responses_utils.py
@@ -348,6 +348,38 @@ class TestResponseAPILoggingUtils:
         assert result.completion_tokens_details.image_tokens == 100
         assert result.completion_tokens_details.text_tokens == 70
 
+    def test_transform_response_api_usage_populates_reasoning_tokens_regression_15377(
+        self,
+    ):
+        """Regression test for issue #15377.
+
+        Azure OpenAI Responses API returns ``usage.output_tokens_details`` with
+        ``reasoning_tokens``. LiteLLM must transform this into
+        ``completion_tokens_details.reasoning_tokens`` on the returned ``Usage``
+        object so downstream callbacks (e.g. ``async_log_success_event``) see
+        the reasoning tokens rather than ``completion_tokens_details=None``.
+        """
+        # Raw usage shape as returned by Azure Responses API for a reasoning model.
+        usage = {
+            "input_tokens": 12,
+            "input_tokens_details": {"cached_tokens": 0},
+            "output_tokens": 204,
+            "output_tokens_details": {"reasoning_tokens": 64},
+            "total_tokens": 216,
+        }
+
+        result = ResponseAPILoggingUtils._transform_response_api_usage_to_chat_usage(
+            usage
+        )
+
+        assert isinstance(result, Usage)
+        # Core fix: completion_tokens_details must be populated, not None.
+        assert result.completion_tokens_details is not None
+        assert result.completion_tokens_details.reasoning_tokens == 64
+        # Sanity check: prompt_tokens_details still behaves as before.
+        assert result.prompt_tokens_details is not None
+        assert result.prompt_tokens_details.cached_tokens == 0
+
 
 class TestResponsesAPIProviderSpecificParams:
     """