FLUX.2 Klein 4B
FLUX.2 [klein] 4B image edit: change or combine up to three source images with a written instruction, in the same small open model, with no content filter.
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FLUX.2 Klein 4B vs FLUX.2 Klein 9B
FLUX.2 Klein 4B lists a 22% lower unit price than FLUX.2 Klein 9B. Tier prices, request fields and limits side by side.
FLUX.2 Klein 9B
FLUX.2 [klein] 9B image editing takes one to three source images and an instruction, keeping a person's face and pose while the clothes, room or light change. Edits usually return in well under a minute.
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The short answer
Start with the input you have, the result you want and your budget. These are the differences that affect that choice.
- FLUX.2 Klein 4B has the lower listed unit price by 22%.
- Both are listed as Uncensored. Compare the examples and content-test details on each model page for the scenes you want to create.
Compare the published examples, then try the same input on both models with matching settings.
Test scores side by side
The Spicy Index and Freedom Score for both models, from the same daily calculation as the leaderboards.
| Measure | FLUX.2 Klein 4B | FLUX.2 Klein 9B |
|---|---|---|
| Spicy Index | 59.6 | 65.0 |
| Freedom Score | 78.6 | 84.0 |
| Evidence | Tested 6 of 6 probe types · 50 runs | Tested 6 of 6 probe types · 50 runs |
| Range if the rest pass | 78.6–78.6 | 84.0–84.0 |
| Price | $0.0093 per image | $0.011 per image |
| Reviews | Read the FLUX.2 Klein 4B review | Read the FLUX.2 Klein 9B review |
Current price
Price at the same setting
A start price answers a different question than the one you have. These are the tiers both models publish, matched setting for setting, in US dollars per billed unit with no conversion step in between.
Swipe horizontally to compare all fields.
| Tier | FLUX.2 Klein 4B | FLUX.2 Klein 9B | Difference |
|---|---|---|---|
| Current price | $0.013 / output images | $0.016 / output images | FLUX.2 Klein 4B −22% |
What one ordinary job costs
- FLUX.2 Klein 4B: $1.26 for one hundred images.
- FLUX.2 Klein 9B: $1.63 for one hundred images.
Arithmetic on the published rates at each model's own default setting, not a quote. The console prices your actual settings before a request is accepted.
About this comparison
Controls and limits
Every row here is read from the JSON Schema the endpoint validates against, so it matches what the API will really accept rather than a feature list written by hand.
Swipe horizontally to compare all fields.
| Controls and limits | FLUX.2 Klein 4B | FLUX.2 Klein 9B |
|---|---|---|
| Supported tasks | image-to-image | image-to-image |
| Resolution tiers | 1K · 2K | 1K · 2K |
| Aspect ratios | auto · 1:1 · 16:9 · 9:16 · 4:3 · 3:4 · 3:2 · 2:3 · 21:9 · 9:21 | auto · 1:1 · 16:9 · 9:16 · 4:3 · 3:4 · 3:2 · 2:3 · 21:9 · 9:21 |
| Reference material | Up to 3 files | Up to 3 files |
| High-resolution tier | Yes | Yes |
| Seed | Yes | Yes |
| Execution | Submit, then poll or take the callback | Submit, then poll or take the callback |
| Request timeout | 30 minutes | 30 minutes |
| Availability | Live | Live |
Do low-filter models allow every request?
Content policy, side by side
Two separate facts sit behind these labels. The first is what we do, which is nothing: no platform content filter, and no maturity flag to set on a request. The second is what each model does on its own, and that is the only part that varies between these two.
FLUX.2 Klein 4B
Uncensored
This model declares no content filter. SpicyAPI forwards the request without adding a platform content scan; legal and consent duties remain with the customer.
FLUX.2 Klein 9B
Uncensored
This model declares no content filter. SpicyAPI forwards the request without adding a platform content scan; legal and consent duties remain with the customer.
Use these content labels to shortlist models, then open each model page for available examples and content-test details.
The label never changes your obligations. Age, consent, real-person likeness and the law where you operate stay with you, and SpicyAPI does not inspect each request.
Can I swap the model ID without changing the request body?
Request body, field by field
The task lifecycle is shared; the body is not. Each endpoint publishes its own JSON Schema and the API validates against that, so this is the list to reconcile before a switch.
- 5 fields appear in both request bodies under the same names. aspect_ratio, image_urls, prompt, resolution, seed
- FLUX.2 Klein 4B accepts no field the other one lacks.
- FLUX.2 Klein 9B accepts no field the other one lacks.
- FLUX.2 Klein 4B requires image_urls, prompt.
- FLUX.2 Klein 9B requires image_urls, prompt.
- Both reject unknown fields outright, so a parameter left over from the other model comes back as a validation error instead of being quietly ignored.
Compare
Moving from one to the other
The model identifiers are black-forest-labs/flux-2-klein-4b/edit and black-forest-labs/flux-2-klein-9b/edit, and both go in the same field of the same request.
Both run the same way: submit the task, then poll it or take the callback. Queueing and retry logic carry over unchanged.
Both use the same submit-and-track flow, but their required inputs may differ. Check each model page before switching.
One key, one balance, one set of spend caps. Both bill to the same account in US dollars, and the per-key daily, monthly and lifetime limits apply to whichever one you call.
Questions developers ask
Which is cheaper, FLUX.2 Klein 4B or FLUX.2 Klein 9B?
Which is cheaper, FLUX.2 Klein 4B or FLUX.2 Klein 9B?
FLUX.2 Klein 4B has the lower listed unit price by 22%. Prices may change; check the estimate shown for your actual settings before submitting.
How long can a single request run?
FLUX.2 Klein 4B allows 30 minutes per task and FLUX.2 Klein 9B allows 30. Those are ceilings rather than typical times — most requests finish far sooner — but they are what your own client timeout has to survive.
Prices and capabilities shown here come from the current public model catalogue. Check each model page for its latest inputs and examples.