FLUX.2 Klein 4B API reference
The smallest, quickest FLUX for rapid drafts
Call FLUX.2 Klein 4B from your own code with one PopNow API key. Below are the exact model IDs to send, every input field the model accepts, what each request costs in credits, and a request you can paste into a terminal.
At a glance
- Made by
- Black Forest Labs
- Output
- Image
- From
- 1.39 credits per image ($0.0139)
- Typical time
- about 31 s
1 credit = $0.01. A task holds the highest possible charge when it is accepted and settles the real amount when it finishes, rounded up to whole credits; failed tasks are not charged. Ask POST /api/v1/jobs/quote for the exact figure before you run.
Create Image
black-forest-labs/flux-2-klein-4b/text-to-image
Price
| Option | Credits (per image) | US dollars |
|---|---|---|
1k | 1.39 | $0.0139 |
2k | 1.49 | $0.0149 |
Parameters
| Field | Type | Default | Allowed | What it does |
|---|---|---|---|---|
promptRequired | string | — | up to 5,000 characters | Describe the subject, setting, light and style in plain sentences. |
aspect_ratioOptional | string | 1:1 | 1:1, 16:9, 9:16, 4:3, 3:4, 3:2, 2:3, 21:9, 9:21 | Output aspect ratio. |
resolutionOptional | string | 1k | 1k, 2k | Output size tier: 1k is about one megapixel, 2k is 2048 pixels on the long side. |
seedOptional | integer | — | 0 to 2147483647 | Random seed for controlled comparisons. |
Example request
This request runs as it is; any field you leave out uses its default. Put your key in POPNOW_API_KEY first.
curl -X POST "https://api.popnow.ai/api/v1/jobs/createTask" \
-H "Authorization: Bearer $POPNOW_API_KEY" \
-H "Content-Type: application/json" \
-H "Idempotency-Key: $(uuidgen)" \
-d '{
"model": "black-forest-labs/flux-2-klein-4b/text-to-image",
"input": {
"prompt": "A cozy reading nook beside a rain-streaked window, warm lamp light, a sleeping orange cat on a knitted blanket, soft film grain",
"resolution": "1k"
}
}'The response carries a taskId straight away. Read the result with GET /api/v1/jobs/recordInfo, or add callBackUrl to be notified.
curl "https://api.popnow.ai/api/v1/jobs/recordInfo?taskId=TASK_ID_FROM_CREATE_TASK" \
-H "Authorization: Bearer $POPNOW_API_KEY"Edit Image
black-forest-labs/flux-2-klein-4b/edit
Price
| Option | Credits (per image) | US dollars |
|---|---|---|
Default | 1.89 | $0.0189 |
Parameters
| Field | Type | Default | Allowed | What it does |
|---|---|---|---|---|
promptRequired | string | — | up to 5,000 characters | Say what to change and what must stay the same. |
image_urlsRequired | array<string (uri)> | — | up to 3 items | One to three source images, in the order your prompt refers to them. |
aspect_ratioOptional | string | auto | auto, 1:1, 16:9, 9:16, 4:3, 3:4, 3:2, 2:3, 21:9, 9:21 | Output aspect ratio; auto keeps the shape of the first source image. |
resolutionOptional | string | 1k | 1k, 2k | Output size tier when you choose an aspect ratio; with auto the result keeps the shape of the first source image. |
seedOptional | integer | — | 0 to 2147483647 | Random seed for controlled comparisons. |
Example request
This request runs as it is; any field you leave out uses its default. Put your key in POPNOW_API_KEY first.
The example uses PopNow sample files in image_urls. Replace them with your own public HTTPS links, uploads or saved assets.
curl -X POST "https://api.popnow.ai/api/v1/jobs/createTask?wait=60" \
-H "Authorization: Bearer $POPNOW_API_KEY" \
-H "Content-Type: application/json" \
-H "Idempotency-Key: $(uuidgen)" \
-d '{
"model": "black-forest-labs/flux-2-klein-4b/edit",
"input": {
"prompt": "Change the orange jacket to deep forest green and add soft golden-hour light; keep the face, pose and background unchanged",
"image_urls": [
"https://media.popnow.ai/influencer/examples/marco.webp"
]
}
}'The response carries a taskId straight away. Read the result with GET /api/v1/jobs/recordInfo, or add callBackUrl to be notified.
curl "https://api.popnow.ai/api/v1/jobs/recordInfo?taskId=TASK_ID_FROM_CREATE_TASK" \
-H "Authorization: Bearer $POPNOW_API_KEY"