GPT Image 2.5 reference images: how many you can send and how to use

GPT Image 2.5 on Sume accepts up to 16 reference images per request, in input_references; ChatGPT Image 2 accepts up to 10. Every URL must be public HTTPS. OpenAI's guide states no maximum for its own edit endpoint and shows examples with several images, so 16 is Sume's catalog limit.

Limits from Sume's Image API docs, read 2026-09-29.

How do I say what each image is for?

Refer to images by order and role: "image 1 is the model, image 2 is the jacket, image 3 is the background". Without roles, the model has to guess which image supplies the subject and which supplies the style.

curl -X POST "https://api.sume.com/v1/images" \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "openai/gpt-image-2.5",
    "prompt": "Image 1 is the person, image 2 is the jacket. Dress the person in the jacket. Keep the pose and background of image 1.",
    "input_references": [
      { "type": "image_url", "image_url": { "url": "https://example.com/person.jpg" } },
      { "type": "image_url", "image_url": { "url": "https://example.com/jacket.jpg" } }
    ],
    "aspect_ratio": "auto"
  }'

Do more references cost more?

Yes: the input image tokens are estimated per reference and added to the output cost, at $8 per million image input tokens per OpenAI's model page. Send only the images the result needs.

What are the limits?