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.
- Base price
- $0.008USD / run
- Execution
- async
- Model type
- image
- Input fields
- 5
Try the model
Playground
Examples
Select an example to load its inputs and result into the playground.
Model card
Specifications
Pricing
- Base price
- $0.008 / run
Context & modalities
- Input
- Schema-defined
- Output
- image
Capabilities
- Chat
- Not supported
- Vision
- Not supported
- Reasoning
- Not supported
- Structured output
- Not supported
- Function calling
- Not supported
- Audio input
- Not supported
Access
- Provider
- BFL
- Model ID
- bfl/flux-2/klein/4b
- Execution
- async
- Base URL
- https://api.sandbase.ai
- API
- Unified Run API
- Endpoint
- /v1/run
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
- #91 of 102
- Elo
- 840 ±13
- Gap to #1
- −377
Text-to-image arena: people pick the better of two images generated from the same prompt, without seeing the model names.
- #86LongCat Image862±21
- #87FLUX1.1 [pro] Ultra856±20
- #88Lucid Origin Fast851±19
- #89FIBO848±21
- #90Luma Photon846±21
- #91FLUX.2 [klein] 4B840±13
- #92Phoenix 0.9 Ultra840±21
- #93Phoenix 1.0 Fast835±22
- #94FLUX.1 Krea [dev]828±21
- #95FIBO Lite814±17
API README
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 | $0.008 |
Failed runs are not charged.
Prompting
- Write subject, setting, composition, style, then light.
- Quote any text that must appear.
Limits
- One output image per request.
Also on SandBase
Other FLUX.2 endpoints: bfl/flux-2/max, bfl/flux-2/pro, bfl/flux-2/flex, bfl/flux-2/dev, bfl/flux-2/klein/4b/edit.
Start building
Send your first request
OpenAI-compatible endpoint with unified authentication and usage tracking.
# The quoted heredoc keeps Unicode and shell metacharacters unchanged.
result=$(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"Choose your model
Compare models
| Model | Type | Default price | Released |
|---|---|---|---|
Flux 2 Klein 4B Text to ImageThis model BFL | Image | $0.01 / run | Jan 15, 2026 |
BFL | Image | $0.05 / run | Oct 1, 2026 |
BFL | Image | $0.05 / run | Oct 1, 2026 |
BFL | Image | $0.02 / run | Jan 15, 2026 |
BFL | Image | $0.02 / run | Jan 15, 2026 |
BFL | Image | $0.01 / run | Jan 15, 2026 |
Questions
FAQ
How do I call BFL Flux 2 Klein 4B Text to Image through SandBase?
Create a SandBase API key, then send requests with the model ID "bfl/flux-2/klein/4b" to Unified Run API (/v1/run) at https://api.sandbase.ai. The request examples on this page show the exact payload.
Do I need a separate BFL account?
No. One SandBase API key and balance gives you access to BFL Flux 2 Klein 4B Text to Image and the other models in the catalog; you do not need to sign up with BFL separately.

