Openrouter gemini image generation
/SKILLFix for OpenRouter image generation with Gemini/Nano Banana models returning 404 or 400 errors.
--- name: openrouter-gemini-image-generation description: | Fix for OpenRouter image generation with Gemini/Nano Banana models returning 404 or 400 errors. Use when: (1) OpenRouter API returns 404 Not Found for image generation, (2) getting 400 Bad Request with "Invalid option" for aspect_ratio, (3) response parsing fails with "error decoding response body", (4) using /images/generations endpoint with Nano Banana or Gemini image models. The fix is to use /chat/completions endpoint with modalities parameter instead of the images endpoint. author: Claude Code version: 1.0.0 date: 2026-01-21 --- # OpenRouter Gemini Image Generation ## Problem OpenRouter's Gemini image models (Nano Banana, Nano Banana Pro) don't work with the standard /images/generations endpoint. Using this endpoint returns 404 errors, and even when the endpoint seems correct, aspect ratio validation and response parsing can fail. ## Context / Trigger Conditions - Error: OpenRouter API error 404 Not Found when calling /api/v1/images/generations - Error: 400 Bad Request with message about invalid aspect_ratio values - Error: Failed to parse response: error decoding response body - Using models: google/gemini-3-pro-image-preview (Nano Banana Pro) or google/gemini-2.5-flash-image (Nano Banana) ## Solution ### 1. Use Chat Completions Endpoint Instead of /api/v1/images/generations, use /api/v1/chat/completions: ``rust let response = client .post("https://openrouter.ai/api/v1/chat/completions") .header("Authorization", format!("Bearer {}", api_key)) .header("Content-Type", "application/json") .json(&request) .send() .await?; ` ### 2. Include Modalities Parameter The request must include modalities: ["image", "text"]: `json { "model": "google/gemini-3-pro-image-preview", "messages": [ {"role": "user", "content": "Create a professional blog header image..."} ], "modalities": ["image", "text"], "image_config": { "aspect_ratio": "16:9" } } ` ### 3. Use Valid Aspect Ratios Only Valid values: 1:1, 2:3, 3:2, 3:4, 4:3, 4:5, 5:4, 9:16, 16:9, 21:9 **Invalid values that will cause 400 errors:** - 1.91:1 (use 16:9 instead for social media images) - Custom ratios like 1200x630 format ### 4. Parse Nested Response Structure Images are nested in the response: `json { "choices": [{ "message": { "role": "assistant", "content": "I've generated the image.", "images": [{ "type": "image_url", "image_url": { "url": "data:image/png;base64,iVBORw0KGgo..." } }] } }] } ` Extract image bytes from: choices[0].message.images[0].image_url.url ## Verification - API returns 200 status - Response contains choices[0].message.images array with at least one image - Image URL starts with data:image/png;base64, (or similar) - After base64 decoding, bytes represent valid image data ## Example `rust // Request structure #[derive(Serialize)] struct ChatCompletionsRequest { model: String, messages: Vec<ChatMessage>, modalities: Vec<String>, #[serde(skip_serializing_if = "Option::is_none")] image_config: Option<ImageConfig>, } #[derive(Serialize)] struct ImageConfig { aspect_ratio: String, } // Response structure #[derive(Deserialize)] struct ChatCompletionsResponse { choices: Vec<ChatChoice>, } #[derive(Deserialize)] struct ChatChoice { message: AssistantMessage, } #[derive(Deserialize)] struct AssistantMessage { #[serde(default)] images: Vec<ImageObject>, } #[derive(Deserialize)] struct ImageObject { image_url: ImageUrlData, } #[derive(Deserialize)] struct ImageUrlData { url: String, // "data:image/png;base64,..." } // Usage let request = ChatCompletionsRequest { model: "google/gemini-3-pro-image-preview".to_string(), messages: vec![ChatMessage { role: "user".to_string(), content: prompt.to_string(), }], modalities: vec!["image".to_string(), "text".to_string()], image_config: Some(ImageConfig { aspect_ratio: "16:9".to_string(), }), }; ` ## Notes - Nano Banana Pro (google/gemini-3-pro-image-preview) is paid ($2/M input, $12/M output tokens) - Nano Banana (google/gemini-2.5-flash-image) is cheaper ($0.30/M input, $2.50/M output tokens) - Image generation can take 20-30+ seconds - The content` field in the response may contain descriptive text about the generated image ## References - OpenRouter Image Generation Docs - Nano Banana Pro Model Page - Nano Banana Model Page
