Answer: Nano Banana 2.1 is cheaper for iteration — 3 credits at 1K, 4 at 2K, 5 at 4K. GPT Image 2.5 costs 3–35 credits because it splits output into resolution × quality, and at default settings (1K + high) it is 6 credits. For type and layout, GPT Image 2.5's higher cells are usually worth it; for volume and large rasters, Nano Banana 2.1 wins.
Both are priced per image in the same credit pool on Callirra, so the comparison is honest: one credit is $0.01 on either.
The two price shapes
| Nano Banana 2.1 | Credits | USD |
|---|---|---|
| 1K | 3 | $0.03 |
| 2K | 4 | $0.04 |
| 4K | 5 | $0.05 |
| GPT Image 2.5 | low | medium | high | xhigh | max |
|---|---|---|---|---|---|
| 1K | 3 | 4 | 6 | 9 | 13 |
| 2K | 5 | 7 | 10 | 15 | 22 |
| 4K | 8 | 11 | 16 | 24 | 35 |
One is a three-step ladder. The other is a fifteen-cell matrix. That is the whole difference in shape — and the reason "which is cheaper" has no single answer.
Where each one is cheaper
| What you need | Cheaper choice | Why |
|---|---|---|
| 4K anything | Nano Banana 2.1 (5) | GPT's cheapest 4K is 8, at low quality |
| 20 rough drafts | Nano Banana 2.1 (60 total) | GPT's cheapest cell is 3, but its default is 6 |
| Exact type, posters, UI | GPT Image 2.5 at 1K–2K + xhigh | Typography is the quality axis's job |
| Photographic light | GPT Image 2.5 Flare | Same price, better on light-dominated frames |
| Transparent background | GPT Image 2.5 | Nano Banana 2.1 has no background or quality controls |
| Extreme panorama (1:8, 8:1) | Nano Banana 2.1 at 2K/4K | GPT Image 2.5 tops out at 21:9 |
Cost per usable image, not per image
The listed price is per render. What you budget is per kept render:
| Hit rate | Nano Banana 2.1 1K | GPT Image 2.5 1K high |
|---|---|---|
| 1 in 2 | 6 credits | 12 credits |
| 1 in 3 | 9 credits | 18 credits |
| 1 in 4 | 12 credits | 24 credits |
At a 1-in-4 hit rate, a 3-credit render costs 12 credits per usable image. That is the number to compare against a more expensive model that lands in one take — and against a workflow where you fix the prompt instead of pulling again.
The reference budgets are different too
- Nano Banana 2.1: up to 14 references, and Google documents a split of up to 4 character references and up to 10 object references.
- GPT Image 2.5: up to 16 references, plus prompts up to 20,000 characters and eleven aspect ratios.
More references is not automatically better — past the useful set they average the subject — but if your composition needs a cast of four plus product detail, both models can hold it.
What I would do with both
- Explore on Nano Banana 2.1 at 1K (3 credits). It is the cheapest full-resolution draft in the stack, and the 4K step later is one credit.
- Promote the ones with type or layout to GPT Image 2.5 at 1K high (6) or xhigh (9), not 4K low — resolution does not fix letterforms.
- Finish anything print-sized on Nano Banana 2.1 4K (5), unless the frame needs GPT's background control.
That pipeline costs less than committing to either model's mid-tier for everything, and it is the reason both are in the same account.
FAQ
Is Nano Banana 2.1 strictly cheaper? At the same resolution and no quality control, yes. It is also the cheaper 4K route.
Does GPT Image 2.5 have a 3-credit option? Yes, 1K + low (3) — the same as Nano Banana's 1K, with a much lower quality ceiling.
Which handles text better? GPT Image 2.5's quality axis at high and above is the strongest option here; Nano Banana 2.1 is strong too, and cheaper, so test both with your own copy.
Can I switch models after rendering? You can re-render, but it is a new charge — pick the model before the batch.
Both price tables, with a quote before every render, are on Callirra's image pricing page. If you have a brief where the cheaper model won on a job it should not have, that is a useful exception — the rule above is a budget heuristic, not a law.