seedinteger
The seed to use for the generation. If not provided, a random seed will be used.
Flux 2 Klein 4B Text to Image
bfl/flux-2/klein/4bFlux 2 Klein 4b is BFL's advanced text-to-image AI model. Create photorealistic images, illustrations, and concept art from natural language descriptions with exceptional detail and prompt adherence.
Try the model
Playground
Input
The prompt to generate an image from.
Additional Settings More
Customize your input with more control.
48
The number of inference steps to perform. Range: 4 to 8.
The format of the generated image. Allowed values: jpeg, png.
The aspect ratio of the generated image. Allowed values: 21:9, 16:9, 3:2, 4:3, 5:4, 1:1, 4:5, 3:4, 2:3, 9:16.
The seed to use for the generation. If not provided, a random seed will be used.
ResultExample
What would you like to do next?
Examples
Select an example to load its inputs and result into the playground.
- Open result ↗
Input
{ "prompt": "Cheetah in pre-sprint crouch, muscles tensed, gazelle visible in distance, African savanna golden grass, dust particles in air, National Geographic wildlife photography" }
Human preference
Arena
Elo ratings from blind side-by-side votes, compared with other image and video models.
Rankings sourced from Artificial Analysis Arena
- Leaderboard
- Text to Image
- Rank
- #96 of 106
- Elo
- 837 ±12
- Gap to #1
- −385
Text-to-image arena: people pick the better of two images generated from the same prompt, without seeing the model names.
- #91Lucid Origin Fast860±18
- #92LongCat Image856±19
- #93FLUX1.1 [pro] Ultra855±19
- #94FIBO849±19
- #95Luma Photon843±19
- #96FLUX.2 [klein] 4B837±12
- #97Phoenix 0.9 Ultra833±20
- #98Phoenix 1.0 Fast827±20
- #99SRPO826±20
- #100FLUX.1 [dev]823±45
Flux 2 Klein 4B Text to Image
FLUX.2 [klein] 4B, the smallest FLUX.2 model, built for speed. Text to image.
Fields
| Field | Type | Default | Notes |
|---|---|---|---|
prompt | string, required | — | Text instruction. |
num_inference_steps | integer 4–8 | 4 | More steps add detail and time. |
output_format | jpeg / png | png | Output file format. |
aspect_ratio | 21:9 / 16:9 / 3:2 / 4:3 / 5:4 / 1:1 / 4:5 / 3:4 / 2:3 / 9:16 | 16:9 | Output shape. |
seed | integer | random | Fix it to compare prompt changes. |
Billing
$0.008 per image.
| Request | Price |
|---|---|
| One image | $0.008 |
Failed runs are not charged.
Prompting
- Write subject, setting, composition, style, then light.
- Quote any text that must appear.
Limits
- One output image per request.
Also on SandBase
Other FLUX.2 endpoints: bfl/flux-2/max, bfl/flux-2/pro, bfl/flux-2/flex, bfl/flux-2/dev, bfl/flux-2/klein/4b/edit.
Start building
Send your first request
Submit this model through the SandBase Unified Run API.
# The quoted heredoc keeps Unicode and shell metacharacters unchanged.
result=$(curl --fail-with-body --silent \
-X POST "https://api.sandbase.ai/v1/run" \
-H "Authorization: Bearer $SANDBASE_API_KEY" \
-H "Content-Type: application/json" \
--data-binary @- <<'SANDBASE_JSON'
{
"model": "bfl/flux-2/klein/4b",
"prompt": "Cheetah in pre-sprint crouch, muscles tensed, gazelle visible in distance, African savanna golden grass, dust particles in air, National Geographic wildlife photography",
"aspect_ratio": "16:9",
"output_format": "png",
"num_inference_steps": 4
}
SANDBASE_JSON
)
run_id=$(printf '%s' "$result" | jq -r .id)
for attempt in $(seq 1 120); do
status=$(printf '%s' "$result" | jq -r .status)
case "$status" in completed|failed|timeout) break ;; esac
sleep 2
result=$(curl --fail-with-body --silent \
-H "Authorization: Bearer $SANDBASE_API_KEY" \
"https://api.sandbase.ai/v1/run/$run_id")
done
status=$(printf '%s' "$result" | jq -r .status)
[ "$status" = completed ] || { echo "Generation ended: $status" >&2; exit 1; }
printf '%s\n' "$result"2. Authentication
Create a SandBase API key and set it in your server environment. All requests use Bearer authentication.
export SANDBASE_API_KEY="YOUR_API_KEY"Keep the key on your server. Do not expose it in browser code or commit it to a repository.
3. Queue
Submit a request
POST to /v1/run with this model ID and its inputs. The request example above includes submission and polling.
Fetch request status and result
Use the returned run ID to poll until the status is completed, failed or timeout. Read output only after completed.
curl "https://api.sandbase.ai/v1/run/$RUN_ID" \
-H "Authorization: Bearer $SANDBASE_API_KEY"4. Files
Hosted files
Pass a publicly accessible file URL in the model’s image, video or audio field. Supported formats and limits are shown beside each Playground input.
Uploading images
Use the upload or replace control on supported image fields in the Playground. Video URL fields accept a hosted driving video; they do not imply video-upload support.
5. Schema
Input
promptstringrequired
The prompt to generate an image from.
aspect_ratiostring
The aspect ratio of the generated image.
Default: "16:9"
Possible values: "21:9", "16:9", "3:2", "4:3", "5:4", "1:1", "4:5", "3:4", "2:3", "9:16"
output_formatstring
The format of the generated image.
Default: "png"
Possible values: "jpeg", "png"
num_inference_stepsinteger
The number of inference steps to perform.
Default: 4
Minimum: 4
Maximum: 8
{
"model": "bfl/flux-2/klein/4b",
"prompt": "Cheetah in pre-sprint crouch, muscles tensed, gazelle visible in distance, African savanna golden grass, dust particles in air, National Geographic wildlife photography",
"aspect_ratio": "16:9",
"output_format": "png",
"num_inference_steps": 4
}Output
A completed run exposes its result in output. The following is the model’s saved example, not a new generation.
[
{
"source": "BFL/FLUX schema mirror",
"source_url": "https://docs.bfl.ai/flux_2/flux2_overview",
"url": "https://static.sandbase.ai/examples/1362ee2e-4e35-4a9b-b020-81fe119f9140/output/81dd4bd6-e4e3-4129-a165-a99062f20917.png"
}
]