Flux 2 Klein

# Flux 2 Klein — Pro Pack on RunComfy

[runcomfy.com](https://www.runcomfy.com/?utm_source=skills.sh&utm_medium=skill&utm_campaign=flux-2-klein) · [9B model](https://www.runcomfy.com/models/blackforestlabs/flux-2-klein/9b/text-to-image?utm_source=skills.sh&utm_medium=skill&utm_campaign=flux-2-klein) · [4B model](https://www.runcomfy.com/models/blackforestlabs/flux-2-klein/4b/text-to-image?utm_source=skills.sh&utm_medium=skill&utm_campaign=flux-2-klein) · [GitHub](https://github.com/agentspace-so/runcomfy-skills/tree/main/flux-2-klein)

Black Forest Labs' **Flux 2 Klein** (the distilled, low-latency variant of Flux 2) hosted on the **RunComfy Model API** — no API key, async REST.

```bash npx skills add agentspace-so/runcomfy-skills --skill flux-2-klein -g ```

## When to pick this model (vs siblings)

Flux 2 Klein's distinct strength is **latency-first creative iteration**: sub-second feedback enables live art-direction sessions and rapid product visualization that batch-style models can't sustain. Pick it when **iteration speed matters more than ceiling resolution**.

| You want | Use | |---|---| | Real-time / live art-direction sessions | **Flux 2 Klein 4B** | | Fast iteration with strong detail at the end | **Flux 2 Klein 9B** | | Multi-reference brand styling with consistent looks | **Flux 2 Klein** | | 2K–4K hero images, max resolution | Seedream 5 | | Maximum prompt adherence + extreme detail | Flux 2 Pro | | Embedded text, logos, multilingual signage | GPT Image 2 | | Hyperrealistic portrait | Nano Banana Pro |

If the user said "Flux 2 Klein" / "BFL Klein" / "flux klein" explicitly, route here regardless. If they said "Flux 2" generically, ask whether they want **Klein** (fast) or **Pro** (max quality) before defaulting.

## Prerequisites

1. **RunComfy CLI** — `npm i -g @runcomfy/cli` 2. **RunComfy account** — `runcomfy login` opens a browser device-code flow. 3. **CI / containers** — set `RUNCOMFY_TOKEN=<token>` instead of `runcomfy login`.

## Endpoints + input schema

Two variants, same endpoint shape, same prompt grammar.

### `blackforestlabs/flux-2-klein/9b/text-to-image`

The fidelity-first variant. Use for polish / final output.

| Field | Type | Required | Default | Notes | |---|---|---|---|---| | `prompt` | string | yes | — | Up to ~512 tokens. Longer degrades. | | `steps` | int | no | 25 | 4–50. **Step-distilled architecture** — 4–8 enough for concepting; ~25 for polish; >25 buys little. | | `width` | int | no | 1024 | 512–1536 typical. **Aspect ratio capped at 16:9**, max ~2K total. | | `height` | int | no | 1024 | Match `width`'s aspect intent. |

### `blackforestlabs/flux-2-klein/4b/text-to-image`

The latency-first variant. Sub-second 4-step inference. Use for live iteration / concepting.

Same field set as 9B. Default `steps` is effectively 4 — the variant is built for that step count.

### Reference images (both variants)

Up to **4 simultaneous reference images** are supported on the same endpoint for style transfer / guided composition. The exact field name in the JSON body is documented on the [model's API tab](https://www.runcomfy.com/models/blackforestlabs/flux-2-klein/9b/text-to-image?utm_source=skills.sh&utm_medium=skill&utm_campaign=flux-2-klein) — pass it through the CLI verbatim. Reference-image use enables editing-style workflows without a separate `/edit` endpoint.

## How to invoke

**Fast concepting (4B, sub-second):**

```bash runcomfy run blackforestlabs/flux-2-klein/4b/text-to-image \ --input '{"prompt": "<user prompt>"}' \ --output-dir <absolute/path> ```

**Polish / final (9B, ~25 steps):**

```bash runcomfy run blackforestlabs/flux-2-klein/9b/text-to-image \ --input '{ "prompt": "<user prompt>", "steps": 25, "width": 1024, "height": 1024 }' \ --output-dir <absolute/path> ```

**Wide-format poster:**

```bash runcomfy run blackforestlabs/flux-2-klein/9b/text-to-image \ --input '{"prompt": "<user prompt>", "width": 1536, "height": 864}' \ --output-dir <absolute/path> ```

The CLI submits, polls every 2s until terminal, then downloads any `*.runcomfy.net` / `*.runcomfy.com` URL from the result into `--output-dir`. Stdout is the result JSON. Stderr is progress.

For pipe-friendly usage:

```bash runcomfy --output json run blackforestlabs/flux-2-klein/4b/text-to-image \ --input '{"prompt":"..."}' --no-wait | jq -r .request_id ```

## Prompting — what actually works

These are model-specific patterns that empirically improve output quality.

**Subject-first declarative grammar.** The structure Flux 2 Klein was trained on is *"Subject + action + scene + style + lighting + camera + quality"*. Front-load the subject; trail with directives. Example: `"A vibrant hummingbird mid-flight sipping nectar from a bright pink hibiscus, iridescent feathers in morning sun, soft bokeh tropical garden, macro photography, razor-sharp detail, cinematic lighting"`.

**Specificity wins over flowery language.** "4k product photo, softbox lighting, reflectiv