Steam bundle header 707x232: what an AI image can hit

Steam's Bundle Header is 707x232 pixels, and an image request to Sume cannot return exactly that. The ratio is about 3.05:1, over the 3:1 limit on custom sizes, and 707 is odd. Generate a 3:1 image, then crop to 707x232 in your own tool.

Steam sizes are from the Steamworks store-assets page; request limits are from Sume's image docs, both read 2026-10-01.

What sizes does Steam list for these two assets?

The page lists the Bundle Header at 707x232 and the Page Background at 1438x810, which Steam marks optional because it is auto-generated from screenshots when you do not supply one.

Which Sume limits block 707x232?

For ChatGPT Image 2.5 (openai/gpt-image-2.5), the docs say image_size accepts custom pixels where "both edges must be multiples of 16, with a maximum edge of 3840, aspect ratio at most 3:1, and 655,360–8,294,400 pixels." 707 is not a multiple of 16, 707x232 is about 164,000 pixels (under the 655,360 floor), and the ratio is over 3:1. Three limits, any one of which rules it out.

What should I request instead?

Ask for a 3:1 canvas that meets the pixel floor, for example 1440x480 (both multiples of 16, 691,200 pixels). Keep the logo and key art away from the top and bottom edges, because 707x232 is slightly wider than 3:1, so the crop trims a few pixels of height. For the Page Background, aspect_ratio: "16:9" is in the supported list; resize to 1438x810 afterward.

If a different model is selected, use its aspect_ratio values rather than custom pixels; the list in the docs has no 8:5 or 16:10 and no odd sizes. For the neighbouring Steam assets see Steam capsule sizes.

Does Sume do the final resize?

The image docs describe requested ratios and sizes, not an exact-pixel finishing step. Treat the generated file as source art and export the exact Steam dimensions from your image editor or build script, then check them against the Steamworks page before uploading.