From 19f8c63cf6dedca43e7bf443b7abb3793fe63574 Mon Sep 17 00:00:00 2001
From: PRABHU KIRAN VANDRANKI <72809214+VANDRANKI@users.noreply.github.com>
Date: Wed, 6 May 2026 15:34:34 -0400
Subject: [PATCH] fix(logging): prevent AnthropicResponse ValidationError for
 Responses API events in anthropic_messages logging

When the experimental Anthropic pass-through adapter routes a request through
the Responses API backend (e.g. Azure/Foundry), the success handler in
_handle_anthropic_messages_response_logging() receives a ResponseIncompleteEvent
or ResponseCompletedEvent object from the Responses API stream. These types are
not dict-serialisable as AnthropicResponse, so AnthropicResponse.model_validate()
raises a ValidationError in background (non-blocking) logging:

  1 validation error for AnthropicResponse
  Input should be a valid dictionary or instance of AnthropicResponse
  [type=model_type, input_value=ResponseIncompleteEvent(...)]

Fix: add isinstance guards for ResponseCompletedEvent / ResponseIncompleteEvent
before the model_validate call, and also guard any other non-dict, non-
AnthropicResponse type. When the guard triggers, emit a debug-level log and
return the result as-is so downstream logging continues without crashing.

Fixes #27091
---
 litellm/litellm_core_utils/litellm_logging.py | 27 +++++++++++++++++++
 1 file changed, 27 insertions(+)

diff --git a/litellm/litellm_core_utils/litellm_logging.py b/litellm/litellm_core_utils/litellm_logging.py
index fd14f55add3..c270797455b 100644
--- a/litellm/litellm_core_utils/litellm_logging.py
+++ b/litellm/litellm_core_utils/litellm_logging.py
@@ -3446,6 +3446,33 @@ class Logging(LiteLLMLoggingBaseClass):
             )
         else:
             from litellm.types.llms.anthropic import AnthropicResponse
+            from litellm.types.llms.openai import (
+                ResponseCompletedEvent,
+                ResponseIncompleteEvent,
+            )
+
+            # When the experimental Anthropic pass-through adapter routes a request
+            # through the Responses API (e.g. to Azure/Foundry), the success handler
+            # may receive a ResponseIncompleteEvent or ResponseCompletedEvent rather
+            # than a plain dict or AnthropicResponse instance.
+            # AnthropicResponse.model_validate() rejects these types and raises a
+            # ValidationError in background logging (non-blocking but noisy).
+            # Guard against this before calling model_validate. (Fixes #27091)
+            if isinstance(result, (ResponseCompletedEvent, ResponseIncompleteEvent)):
+                verbose_logger.debug(
+                    "anthropic_messages logging: result is a Responses API event (%s), "
+                    "skipping AnthropicResponse transform",
+                    type(result).__name__,
+                )
+                return result  # type: ignore[return-value]
+
+            if not isinstance(result, (dict, AnthropicResponse)):
+                verbose_logger.debug(
+                    "anthropic_messages logging: unexpected result type %s, "
+                    "skipping AnthropicResponse transform",
+                    type(result).__name__,
+                )
+                return result  # type: ignore[return-value]
 
             pydantic_result = AnthropicResponse.model_validate(result)
             import httpx