[Bug Fix]: ErrorEvent ValidationError when OpenAI Responses API returns nested error structure (#15804)

* add ErrorEventError nested field

* test_openai_responses_api_token_limit_error

* test_openai_responses_api_token_limit_error

litellm/types/llms/openai.py

@@ -1408,13 +1408,20 @@ class ImageGenerationPartialImageEvent(BaseLiteLLMOpenAIResponseObject):
     b64_json: str
 
 
-class ErrorEvent(BaseLiteLLMOpenAIResponseObject):
-    type: Literal[ResponsesAPIStreamEvents.ERROR]
-    code: Optional[str]
+class ErrorEventError(BaseLiteLLMOpenAIResponseObject):
+    """Nested error object within ErrorEvent"""
+    type: str  # e.g., 'invalid_request_error'
+    code: str  # e.g., 'context_length_exceeded'
     message: str
     param: Optional[str]
 
 
+class ErrorEvent(BaseLiteLLMOpenAIResponseObject):
+    type: Literal[ResponsesAPIStreamEvents.ERROR]
+    sequence_number: int
+    error: ErrorEventError
+
+
 class GenericEvent(BaseLiteLLMOpenAIResponseObject):
     type: str
 

tests/llm_responses_api_testing/test_openai_responses_api.py

@@ -1508,3 +1508,29 @@ async def test_basic_openai_responses_with_websearch(stream):
             print("chunk=", json.dumps(chunk, indent=4, default=str))
     else:
         print("response=", json.dumps(response, indent=4, default=str))
+
+
+@pytest.mark.asyncio
+async def test_openai_responses_api_token_limit_error():
+    """
+    Relevant issue: https://github.com/BerriAI/litellm/issues/15785
+
+
+    When this fails you'll see:
+    "pydantic_core._pydantic_core.ValidationError: 3 validation errors for ErrorEvent"
+    in the console.
+    """
+    litellm._turn_on_debug()
+
+    # Generate text with >400k tokens to trigger token limit error
+    oversized_text = "This is a test sentence. " * 50000  # ~400k tokens
+
+    # This will raise ValidationError instead of showing the real error
+    response = await litellm.aresponses(
+        model="gpt-5-mini",
+        input=oversized_text,
+        stream=True
+    )
+
+    async for event in response:
+        print(event)  # Never reaches here - ValidationError is raised