30 slide backgrounds in 16:9: $4.50 on Nano Banana 2.1, $1.67 on GPT

The short answer

Thirty 16:9 slide backgrounds at 2K cost $4.50 on Sume with Nano Banana 2.1 (30 x $0.15) and $1.67 with GPT Image 2.5 medium (30 x $0.055625 = $1.66875). The 1K Nano Banana 2.1 total is $3.00.

Slide backgrounds are a low-risk use for a new model because nobody reads them closely. That makes them a cheap way to test the two launches this week against each other before moving a real workflow.

The arithmetic

A deck rarely needs 30 unique backgrounds. Most decks use five or six and repeat them, so the more realistic bill is the cost of six backgrounds, which is $0.90 on Nano Banana 2.1 at 2K. The table prices the full 30 as a ceiling.

Ask for the same 16:9 ratio on every call so that backgrounds swap between slides without cropping.

How to run it

Generate five prompts at n set to 4 and keep the best from each, which is 20 images and $3.00 at 2K on Nano Banana 2.1. That is cheaper than 30 single calls and gives you a choice.

Keep the center of the image quiet in the prompt so title text stays readable once you place it over the picture.

Retries and cost per slide

Some images will be rejected by eye, and rejected images are billed like any other, so budget a margin. The bullets add 20 percent to each Sume total in the table above (the totals multiplied by 1.2) and divide by the number of slides to give a per-slide cost.

Treat the per-slide figure as the number to compare across models, because it does not change when the count changes. Re-read the public catalog before a large run, since prices can change and the table is a snapshot from 2026-10-08.

• Nano Banana 2.1 at 2K: $4.50 becomes $5.40 with 20 percent extra images, which is $0.18 per slide (a 30-slide job).
• Nano Banana 2.1 at 1K: $3.00 becomes $3.60 with 20 percent extra images, which is $0.12 per slide (a 30-slide job).
• GPT Image 2.5 medium (2K): $1.67 becomes $2.00 with 20 percent extra images, which is $0.07 per slide (a 30-slide job).
• GPT Image 2.5 low (1K): $0.74 becomes $0.89 with 20 percent extra images, which is $0.03 per slide (a 30-slide job).

What the docs say to check

The n parameter takes up to 10 images per call, but per-model ceilings are lower, so read the n range descriptor for the model before you plan the number of calls.

The endpoint pricing lines are what Sume charges your wallet and already include the Sume margin, so a call costs cost_usd times n. Sume bills image generation all or nothing: a generation that fails or is cancelled is not charged.

If you need the same look across all slides, send your first approved background as an input reference for the others.

The numbers above are list prices read on 2026-10-08, not measurements. Sume figures are the catalog prices that already include its margin, Google figures are from its own pricing page, and quality or speed differences are not covered. Re-read both pages before you commit a large budget, because either side can change its rates.