One hero at 4K: Nano Banana 2.1 $0.20, 2K plus upscale $0.35

The short answer

Nano Banana 2.1 at native 4K costs $0.20 per image on Sume. Rendering at 2K ($0.15) and then running the image upscale ($0.20) costs $0.35, and Nano Banana Pro at 4K costs $0.375. If the generator can make the 4K frame itself, the upscale route is the dearer way to reach 4K.

The upscale earns its place when you already have a 2K or smaller image you want to keep, not when you are starting fresh.

Three routes to a 4K hero

Native: one call with resolution set to 4K. Step-up: generate at 2K, then submit the result to the image upscale model at a flat price per image. Pro: the same native call on the higher-priced model. The Image API sends resolution as a normalized tier of 0.5K, 1K, 2K or 4K for the banana models.

The step-up route also takes two jobs and two waits instead of one.

When the step-up is right

Say a client approves 5 of 18 heroes at 2K and only those need 4K for print. Generating all 18 at 2K and upscaling 5 costs 18 x $0.15 + 5 x $0.20 = $3.70. Going native 4K on all 18 costs $3.60. When the approval rate is low, step-up is cheaper because the 4K spend lands only on winners.

Break-even for 2.1 is where the upscaled share s satisfies 0.15 + 0.20 s = 0.20, so s = 0.25. If more than a quarter of the 2K images get upscaled, native 4K from the start is cheaper.

Notes on quality

The upscale does not add scene detail the way a native render does; whether the difference matters for your print size is a judgement for your own test. The price table does not settle it. Test one image each way before you commit a run.

Both routes bill only on completed jobs, and both return Sume-hosted URLs.

Checking the figures

All four routes use rows read from the public catalog on 2026-10-08. The image upscale is a flat $0.20 per image. Eighteen native 2.1 heroes at 4K cost $3.60, eighteen step-ups cost $6.30, and eighteen Pro 4K images cost $6.75.

The step-up has one more cost that the table does not show: an extra job that you have to submit, poll and fetch. If you automate the pipeline, that is a few lines of code. If a person runs it, it is a few more clicks per image.

Make sure the 2K source is a public HTTPS URL when you submit it to the upscale. Sume-hosted result URLs are signed, so refresh them if the link has expired before you pass it on.

If the hero is for web use, 2K at $0.15 may be enough, and the whole question of 4K cost goes away for that image.