GPT Image 2.5 request cheat sheet: the fields Sume accepts
One table of the ChatGPT Image 2.5 fields on POST /v1/images: ids, references, mask, background, quality, size rules, and what happens past 30 seconds.
ChatGPT Image 2.5 on Sume is openai/gpt-image-2.5 (Flare) and openai/gpt-image-2.5-sunburst, called through POST /v1/images. Both take text-to-image, up to 16 reference images, an optional mask_url, and background. This page collects the fields in one table, from Sume's Image API docs as read on 2026-10-02.
Auto model routing continues to use Flare, per the same docs.
Which fields can I send?
A field the model does not list is rejected with 400 unsupported_parameter. These are listed for ChatGPT Image 2.5.
| Field | Values or rule |
|---|---|
model | openai/gpt-image-2.5 or openai/gpt-image-2.5-sunburst |
input_references | Up to 16 public HTTPS image URLs |
mask_url | Optional public HTTPS mask for edits |
background | auto, transparent, or opaque |
quality | auto, low, medium, high, xhigh, max; default high |
image_size | Preset, auto, or custom pixels |
output_format | png, jpeg, webp |
What are the size rules?
Custom pixels need both edges as multiples of 16, a maximum edge of 3840, an aspect ratio of at most 3:1, and 655,360 to 8,294,400 total pixels. On edits, prefer aspect_ratio: "auto" so the output matches the reference; omitting it is not the same.
How does the response arrive?
mode defaults to sync on this route, with a wait of up to 30 seconds. A generation that outlasts it returns 202 with the job envelope, and you read the images from the standard job result endpoint. mode: "async" and "webhook" return the envelope straight away. Results are Sume-hosted signed URLs in data[].url, and usage.cost is the billed USD amount.
What does not exist?
Native streaming is not served: stream: true returns 400 streaming_not_supported. seed and output_compression return 400 unsupported_parameter. For the current field list, see the Image API docs.
Sources
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