FLUX text-to-image API reference and live debugger — full FLUX.2 [klein/pro/max/flex] family via OpenAI-compatible drop-in, 4MP output and exact hex color control
Bearer sk-xxx), choose model and size, enter the prompt, and send.| Parameter | Type | Required | Default | Description |
|---|---|---|---|---|
model | string | Yes | — | FLUX model ID, see table below |
prompt | string | Yes | — | Prompt, up to 32K tokens. Supports natural language and structured JSON |
size | string | No | 1024x1024 | OpenAI-style size string, e.g., 1920x1080 |
width | integer | No | 1024 | BFL-native, alternative to size, must be multiple of 16 |
height | integer | No | 1024 | BFL-native, must be multiple of 16 |
seed | integer | No | random | Fix for reproducibility |
safety_tolerance | integer | No | 2 | 0 (strictest) – 6 (most permissive) |
output_format | string | No | jpeg | jpeg / png |
prompt_upsampling | boolean | No | false | Auto-expand prompt (not on [klein]) |
steps | integer | No | 50 | Only for flux-2-flex, max 50 |
guidance | number | No | 4.5 | Only for flux-2-flex, 1.5–10 |
n | integer | No | 1 | Only 1 supported |
| Model ID | Speed | Best For |
|---|---|---|
flux-2-max | < 15s | Flagship + grounding search |
flux-2-pro | < 10s | Production at scale, best value |
flux-2-flex | Slower | Typography specialist |
flux-2-klein-9b | Sub-second | Balanced |
flux-2-klein-4b | Sub-second | Fastest |
flux-pro-1.1-ultra | ~10s | Legacy 4MP (see Historical Versions) |
flux-pro-1.1 | ~5s | Legacy 1.6MP |
flux-pro | ~6s | First-gen pro |
flux-dev | ~5s | Dev/test |
usage field (priced per image, not per token). Actual billing follows the pricing table on this site. The response header x-request-id is for support tracing.API Key from the APIYI Console
FLUX model ID. For FLUX.2 prefer flux-2-pro / flux-2-max; legacy versions in the Historical Versions page.
flux-2-max, flux-2-pro, flux-2-flex, flux-2-klein-9b, flux-2-klein-4b, flux-pro-1.1-ultra, flux-pro-1.1, flux-pro, flux-dev Prompt, up to 32K tokens. Supports natural language, hex codes, and structured JSON.
"A cinematic shot of a futuristic city at sunset, 85mm lens"
OpenAI-style size string. Pick either size or width+height.
Common: 1024x1024 / 1536x1024 / 1024x1536 / 1920x1080 / 1440x2048 / 2048x2048.
Custom must satisfy: multiples of 16, 64×64–4MP.
"1920x1080"
BFL-native syntax, alternative to size. Must be a multiple of 16, between 64 and 2048.
64 <= x <= 20481920
BFL-native syntax. Must be a multiple of 16, between 64 and 2048.
64 <= x <= 20481080
Fix for reproducibility — same seed + same other params yields the same result.
42
Moderation level. 0 = strictest, 6 = most permissive, default 2.
0 <= x <= 6Output format.
jpeg, png Auto-expand the prompt. Not supported on FLUX.2 [klein] (silently ignored).
Only flux-2-flex. Inference steps, max 50.
1 <= x <= 50Only flux-2-flex. Guidance scale. 1.5–10, higher = closer to prompt.
1.5 <= x <= 10Number of images. Only 1 supported.
1