BerriAI/litellm · error · OpenRouterException

Error transforming OpenRouter image generation response: {e}

Error message

Error transforming OpenRouter image generation response: {e}

What it means

After JSON parsing succeeds, the OpenRouter image-generation handler maps choices[].message.images[] into ImageResponse objects and attaches usage/cost. Any exception during this transformation is re-raised as an OpenRouterException with a generic status_code=500 and empty headers; the message embeds the original exception.

Source

Thrown at litellm/llms/openrouter/image_generation/transformation.py:396

                                    revised_prompt=None,
                                )
                            )
                        else:
                            model_response.data.append(
                                ImageObject(
                                    b64_json=None,
                                    url=image_url,
                                    revised_prompt=None,
                                )
                            )

            # Extract and set usage and cost information
            self._set_usage_and_cost(model_response, response_json, model)

            return model_response

        except Exception as e:
            raise OpenRouterException(
                message=f"Error transforming OpenRouter image generation response: {e}",
                status_code=500,
                headers={},
            )

    def get_error_class(self, error_message: str, status_code: int, headers: dict | httpx.Headers) -> BaseLLMException:
        """Get the appropriate error class for OpenRouter errors."""
        return OpenRouterException(
            message=error_message,
            status_code=status_code,
            headers=headers,
        )

View on GitHub (pinned to 77b7c6c40c)

Solutions

Turn on litellm verbose logging to capture the raw JSON that failed the mapper
Reproduce with curl and compare against the expected choices[].message.images[] shape
Upgrade litellm to pick up schema fixes
Report to litellm with the sanitized response if the latest version still fails

Defensive patterns

Strategy: try-catch

Try / catch

Catch OpenRouterException; a message starting with 'Error transforming' means the JSON parsed but the schema was unexpected. Keep the raw payload from logs, switch to an alternate image model/provider for the request, and report the schema change upstream.

Prevention

Maintain a fallback image model list so schema drift degrades instead of failing
Capture verbose logs in staging to catch schema changes before production
Track litellm release notes for OpenRouter image-generation fixes

When it happens

Trigger: The parsed JSON lacks or changes the expected structure: missing choices, image entries without url fields, nulls where the mapper expects strings, or OpenRouter shipping a modified image-generation response schema for the requested model.

Common situations: Version drift between litellm and OpenRouter's response format; new models returning extra/renamed fields that the mapper cannot index; intermittent partial payloads under load.

Related errors

AI-assisted analysis of BerriAI/litellm@77b7c6c40c (2026-08-18). Data as JSON: /api/errors/0fbb40ea19205ff7. Report an issue: GitHub.