black-forest-labs/flux-2-klein-9b/text-to-imageFrom 2 credits per image· Create Image

FLUX.2 [klein] 9B is Black Forest Labs' small, fast image model, released on 15 January 2026. One model both generates and edits, with up to three reference images, 1k or 2k output and nine aspect ratios. Most renders came back in 15 to 35 seconds in our tests.

Call it with the model name black-forest-labs/flux-2-klein-9b/text-to-image on POST /jobs/createTask, from 2 credits per image ($0.02). New accounts get 30 free credits to try it in the Playground first.

  • Create Image
  • Edit Image
  • Up to 2K
  • Up to 3 reference images
  • 9 aspect ratios
Model nameblack-forest-labs/flux-2-klein-9b/text-to-image
EndpointPOST https://api.popnow.ai/api/v1/jobs/createTask
# 1. Create the task. Keep the Idempotency-Key if you retry after a network error.
export IDEMPOTENCY_KEY="$(uuidgen)"
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: $IDEMPOTENCY_KEY" \
  -d '{
  "model": "black-forest-labs/flux-2-klein-9b/text-to-image",
  "input": {
    "prompt": "A ceramic teapot on a linen cloth, soft window light, muted palette",
    "aspect_ratio": "1:1",
    "resolution": "1k"
  }
}'

# 2. Copy data.taskId from the response, then poll until state is succeeded, failed, canceled or expired.
TASK_ID="TASK_ID_FROM_RESPONSE"
curl "https://api.popnow.ai/api/v1/jobs/recordInfo?taskId=$TASK_ID" \
  -H "Authorization: Bearer $POPNOW_API_KEY"

The input is built from the schema below, so it passes validation as written. Change the prompt and links to your own.

Price

OptionCredits per image≈ USD
resolution 1K1.65$0.017
resolution 2K1.83$0.018

1 credit = $0.01 · Every option and its price: GET /models/black-forest-labs/flux-2-klein-9b/text-to-image

Each task is rounded up to whole credits, so one run at the lowest tier costs 2 credits per image ($0.02).

Limits

Resolutions
1K · 2K
Aspect ratios
1:1 · 16:9 · 9:16 · 4:3 · 3:4 · 3:2 +3
Prompt length (characters)
5,000

Parameters

These fields come from the same schema we check every request against. Fields that are not listed are rejected.

  • promptstringRequired

    Describe the subject, setting, light and style in plain sentences.

    Range
    1 – 5000 chars
  • aspect_ratiostringOptional

    The shape of the frame: wide, square or tall.

    Default
    "1:1"
    Allowed values
    "1:1""16:9""9:16""4:3""3:4""3:2""2:3""21:9""9:21"
  • resolutionstringOptionalChanges the price

    Output size. Bigger sizes look sharper and cost more.

    Default
    "1k"
    Allowed values
    "1k""2k"
  • seedintegerOptional

    Reuse the same number to get a repeatable result.

    Range
    0 – 2147483647
Raw JSON Schema
{
  "type": "object",
  "required": [
    "prompt"
  ],
  "properties": {
    "seed": {
      "type": "integer",
      "maximum": 2147483647,
      "minimum": 0,
      "description": "Random seed for controlled comparisons."
    },
    "prompt": {
      "type": "string",
      "maxLength": 5000,
      "minLength": 1,
      "description": "Describe the subject, setting, light and style in plain sentences."
    },
    "resolution": {
      "enum": [
        "1k",
        "2k"
      ],
      "type": "string",
      "default": "1k",
      "description": "Output size tier: 1k is about one megapixel, 2k is 2048 pixels on the long side."
    },
    "aspect_ratio": {
      "enum": [
        "1:1",
        "16:9",
        "9:16",
        "4:3",
        "3:4",
        "3:2",
        "2:3",
        "21:9",
        "9:21"
      ],
      "type": "string",
      "default": "1:1",
      "description": "Output aspect ratio."
    }
  },
  "additionalProperties": false
}

Responses, polling and callbacks

Every model works the same way: create a task, then poll it or wait for a callback.

Price it first

cURL
curl -X POST https://api.popnow.ai/api/v1/jobs/quote \
  -H "Authorization: Bearer $POPNOW_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "model": "black-forest-labs/flux-2-klein-9b/text-to-image",
  "input": {
    "prompt": "A ceramic teapot on a linen cloth, soft window light, muted palette",
    "aspect_ratio": "1:1",
    "resolution": "1k"
  }
}'

Same body as createTask. It returns the expected and the highest possible charge, and runs nothing.

Accepted

HTTP
HTTP/1.1 202 Accepted

{
  "code": 200,
  "msg": "success",
  "data": {
    "taskId": "task_01k3m8x9q2z4v7n5p6r8s0t1w3",
    "state": "queued"
  },
  "request_id": "req_example_create"
}

HTTP 202 means the task was accepted and the credits are held, not charged yet. The final charge never goes above the hold.

Check status

cURL
curl "https://api.popnow.ai/api/v1/jobs/recordInfo?taskId=$TASK_ID" \
  -H "Authorization: Bearer $POPNOW_API_KEY"

Poll every few seconds with backoff and stop once state is succeeded, failed, canceled or expired.

Finished task

JSON
{
  "code": 200,
  "msg": "success",
  "data": {
    "taskId": "task_01k3m8x9q2z4v7n5p6r8s0t1w3",
    "model": "black-forest-labs/flux-2-klein-9b/text-to-image",
    "state": "succeeded",
    "output": {
      "assets": [
        {
          "url": "https://cdn.popnow.ai/tasks/task_01k3m8x9q2z4v7n5p6r8s0t1w3/output.png?signature=FROM_RESPONSE",
          "expiresAt": "2026-10-17T12:20:00Z",
          "mime": "image/png",
          "width": 1024,
          "height": 1024
        }
      ]
    },
    "settled": true
  },
  "request_id": "req_example_record"
}

Download from url before expiresAt. Need a fresh link later? Ask POST /common/download-url.

Verify a callback

Node.js
import { createHash, createHmac, timingSafeEqual } from "node:crypto";
import express from "express";

const app = express();
// express.raw keeps the exact bytes that were signed; express.json would not match.
app.post("/hooks/popnow", express.raw({ type: "application/json" }), (req, res) => {
  const timestamp = req.header("X-Webhook-Timestamp");
  const signature = req.header("X-Webhook-Signature") ?? "";
  const body = JSON.parse(req.body.toString("utf8"));
  const taskId = body.data?.taskId ?? body.task_id;
  const digest = createHash("sha256").update(req.body).digest("hex");
  const expected = createHmac("sha256", process.env.POPNOW_WEBHOOK_SECRET)
    .update(`${taskId}.${timestamp}.${digest}`)
    .digest("base64");
  const ok = expected.length === signature.length && timingSafeEqual(Buffer.from(expected), Buffer.from(signature));
  // Check the signature first, then reject anything older than five minutes.
  if (!ok || Math.abs(Date.now() / 1000 - Number(timestamp)) > 300) return res.status(401).end();
  res.status(200).end(); // answer fast, then fetch the task and store its files
});

With callBackUrl set, we post the finished task to you. Check the signature against the raw body before you trust it.

Send a local file

cURL
curl -X POST https://api.popnow.ai/api/v1/common/upload-url \
  -H "Authorization: Bearer $POPNOW_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"contentType": "image/png", "bytes": 482113}'

# PUT the file bytes to data.uploadUrl with every header in data.headers, then commit it:
curl -X POST https://api.popnow.ai/api/v1/files/$FILE_ID/commit \
  -H "Authorization: Bearer $POPNOW_API_KEY"
# The commit returns a popnow://f/... reference. Put it in any image, video or
# audio field of the task input instead of a public https URL.

Public https links work as they are. Local files go through upload-url and commit first.