YouTube channel banner 2560x1440: size, 6 MB cap, API request

YouTube's channel banner API page asks for at least 2048x1152, recommends 2560x1440 at 16:9, allows JPEG or PNG, and caps the file at 6 MB. 2560x1440 is a legal GPT Image 2.5 custom size on Sume, so you can request it directly; the 6 MB cap is the part you must check afterward.

YouTube's figures are from its API docs; the size rules from OpenAI's guide and the Sume Image API docs. Read 2026-10-01; the arithmetic is ours.

What does YouTube require?

Per the channelBanners.insert page: minimum 2048x1152, recommended 2560x1440, 16:9, JPEG or PNG, no more than 6 MB.

What do I send?

OpenAI's guide says sizes above 2560x1440 are experimental; 2560x1440 itself is at the edge. A photo banner compresses better as JPEG, so ask for jpeg.

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": "Wide channel banner, workshop desk with tools, soft light, empty space in the middle, no text",
    "image_size": "2560x1440",
    "output_format": "jpeg"
  }'

How do I stay under 6 MB?

Sume does not serve output_compression in v1, so you cannot set the JPEG quality in the request. Check the downloaded file; if it is over 6 MB, recompress it yourself or drop to 2048x1152.

Will text in the image survive?

OpenAI's guide says text placement and consistency can still be a struggle for GPT Image models, so keep lettering short and add the channel name in your editor if exact spelling matters.