Seedream 4.5 API on Sume: image edits, custom sizes, and 5 Lite

To call the Seedream 4.5 API on Sume, send POST /v1/images with model: "bytedance-seed/seedream-4.5" and a prompt, add up to 10 input_references to edit an image, and size the output with aspect_ratio or custom pixels in image_size. Seedream 5.0 Lite (bytedance-seed/seedream-5-lite) and Seedream 4.0 (bytedance-seed/seedream-4) take the same fields.

The facts below come from the Image API docs, which use Seedream 4.5 in their examples, and the capability descriptors GET /v1/images/models serves, read 2026-09-26. The docs call those descriptors the definitive parameter set, so trust them over any example.

Which Seedream model ids can I send?

All three are edit-capable, with up to 10 reference images each, and the bare legacy ids still work as aliases for the org/slug form. Seedream 4.5 and 5.0 Lite list the same ratios, 1:1, 16:9, 9:16, 4:3, 3:4, 4:5, 5:4, 3:2, 2:3; Seedream 4.0 adds auto.

How do I edit an image with Seedream 4.5?

Put up to 10 public HTTPS image URLs in input_references. The docs recommend aspect_ratio: "auto" on edits, but Seedream 4.5 and 5.0 Lite do not list it, so pick a ratio from their list; Seedream 4.0 accepts auto. The reference array works as in image generation with reference images.

Expect one image per Seedream 4.5 edit. With references, Seedream 4.5 returns a single image even when n is higher, and it does not apply output_format, so send n: 1 on those edits. Seedream 4.5 requests without references apply both fields.

curl -X POST "https://api.sume.com/v1/images" \
  -H "Authorization: Bearer $SUME_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "bytedance-seed/seedream-4.5",
    "prompt": "keep the product identical; swap the background to a soft daylight studio",
    "input_references": [
      { "type": "image_url", "image_url": { "url": "https://example.com/product.png" } }
    ],
    "aspect_ratio": "4:5"
  }'

How do I set a custom size on Seedream?

Seedream is one of the families the docs list for custom pixels, so image_size takes { width, height } or a WIDTHxHEIGHT string, and aspect_ratio is ignored when image_size is set. Named presets work as well; aspect ratios and custom sizes lists them next to every other family's options.

All three Seedream ids list 4:5, the Instagram portrait shape, so that frame needs only aspect_ratio: "4:5", as in the edit example above, and no pixel math.

What does Seedream not accept?

A request that sets a parameter the model does not list is rejected with 400 unsupported_parameter rather than silently dropped. Seedream lists no resolution and no quality, so a body such as resolution: "2K" on Seedream 4.5 fails instead of rendering. Keep these out of Seedream requests:

• resolution, and size, which is only a shorthand for a resolution tier.
• quality.
• mask_url and background, which only the ChatGPT Image 2.5 ids list.
• aspect_ratio: "auto" on Seedream 4.5 and 5.0 Lite, which their lists leave out.

How is Seedream billed?

Per output image. GET /v1/images/models/bytedance-seed/seedream-4.5/endpoints returns the model's pricing line, which already includes Sume's margin, plus a 5.5% agent fee by default; API pricing lists the Image Router at provider list rates times Sume's margin.