AI banner generator: wide banner shapes up to 8:1

An AI banner generator makes a wide image from a text prompt: choose the banner's shape first, generate at that aspect ratio with empty space where the headline goes, and add the words in your design tool. On Sume's Image API, ChatGPT Image 2.5 takes exact pixel sizes up to 3:1, Nano Banana Pro reaches 21:9, and Nano Banana 2 lists shapes as wide as 4:1 and 8:1.

Sume facts come from the Image API docs, the per-model ratio lists that GET /v1/images/models serves, and the request schema in the Sume API reference, read on 2026-09-27. Banners with a platform's fixed size have their own posts: YouTube and LinkedIn.

Which banner shapes can each model make?

Each model publishes its own aspect_ratio list, and it only accepts values on that list. Every catalog model lists 16:9, so the lists differ only in the wider shapes; AI image generation API aspect ratios has every model's full list. Pick the model by the banner's shape:

How do I make a banner at an exact pixel size?

Send the size as a custom image_size to ChatGPT Image 2.5 (openai/gpt-image-2.5). Both edges must be multiples of 16, the longest edge at most 3840, the shape no wider than 3:1, and the total between 655,360 and 8,294,400 pixels. A 1920 × 640 website hero passes all four rules, as in the request below.

• image_size also takes the string form "1920x640", and it wins over aspect_ratio.
• A size that breaks a rule is refused. 1500 × 500 fails because neither 1500 nor 500 is a multiple of 16; ask for 1536 × 512, the same 3:1 shape, and scale it down in your editor.
• The call waits up to 30 seconds. High quality, which this model uses when you omit the field, is one of the slow configurations most likely to return 202 with a job to poll instead of the image.

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": "Website hero banner for a coffee roaster: beans on a dark wooden counter, warm side light, the left third left empty for a headline, no text",
    "image_size": { "width": 1920, "height": 640 }
  }'

What if my banner is wider than 3:1?

Use Nano Banana 2 (google/nano-banana-2), the only catalog model that lists 4:1 and 8:1 today. Send the ratio with a resolution tier: 512, 1K, 2K, or 4K; in current code a request without one runs at 1K. The docs don't give each tier's pixel size, so check the size of the file you get back.

Nano Banana takes no custom pixels. A width and height you send are mapped to the nearest listed ratio, and in current code the exact size is only recorded on the job as target_pixels; Sume does not resize the file. Crop or resize it to your banner's exact size in your own editor.

How do I leave room for the headline?

Say in the prompt where the empty space goes and what fills the rest: the product on the right third, plain sky across the top, a clean wall behind the subject. Ask for no text. Then set the headline, logo, and button in your design tool, where every letter is exact.

Generated lettering can be misspelled, so proofread any words you let the model draw.

What does a banner cost, and what are the limits?

• Each model's per-image rate is in the pricing line of GET /v1/images/models/{model_id}/endpoints, plus a 5.5% agent fee by default; AI image generator API cost compares them. ChatGPT Image 2.5 estimates each request from the image's size and quality, and usage.cost in the response is the USD amount billed to your wallet.
• Billing is all-or-nothing: a failed or cancelled generation is not billed.
• A value a model does not list, such as 4:1 on ChatGPT Image 2.5 or pixels on size, returns 400.
• Results are Sume-hosted, signed URLs in data[].url, so download the banners you keep.