Qwen-Image 2.1 (Model Studio) vs Seedream on BytePlus ModelArk

Qwen-Image 2.1 (Model Studio)

qwen-image-2.1-pro generates and edits images with up to 10 references and transparent output, at $0.04 an image in Singapore, through an OpenAI-compatible endpoint or DashScope. Model Studio publishes a 99.9 per cent SLA and a no-training statement. The model allows 20 requests a minute, has no OpenAPI file, and its open weights are for non-commercial use only.

Seedream on BytePlus ModelArk

Per-image prices from $0.018 are public, and API keys can be limited to named models and an IP allowlist. No status page, SLA or OpenAPI file was found, onboarding needs a browser sign-up, and BytePlus says its model services are not available in the United States.

Qwen-Image 2.1 (Model Studio)

1. Use the same region for the key, the model and the endpoint. Cross-region calls fail
2. Download each result within 24 hours. The URL expires and the image is purged
3. With the OpenAI SDK, pass image, seed, prompt_extend and watermark through extra_body, and write size as 1024x1024, not 1024*1024
4. Set a client timeout of up to 600 seconds for several outputs, or use the async DashScope call and poll the task id
5. Do not send prompt_extend_mode: agent with input images. It returns 400

Seedream on BytePlus ModelArk

1. POST to https://ark.ap-southeast.bytepluses.com/api/v3/images/generations with Authorization: Bearer $ARK_API_KEY. Keys and model activation are per region
2. Set watermark to false if the image must not carry the AI-generated mark. The default is true
3. Download data[].url within 24 hours, or ask for response_format b64_json
4. Check each data[].error in a sequential batch. One moderated image does not fail the others, and only usage.generated_images is billed
5. Stay under 500 images a minute per model and back off with jitter on 429. Layer decomposition reserves 17 against that limit per request