flux-2-klein

Original：🇺🇸 English

Translated

Generate images with Flux 2 Klein (Black Forest Labs' distilled fast variant of Flux 2) on RunComfy — bundled with the model's documented prompting patterns so the skill gets sharper output than naive prompting against the same model. Documents Flux 2 Klein's strengths (sub-second latency, multi-reference brand styling, declarative subject-first prompts), the step-count strategy (4–8 for fast iteration, ~25 for polish), the 9B vs 4B variant trade-off, and when to route to Flux 2 Pro / Seedream 5 / GPT Image 2 instead. Calls `runcomfy run blackforestlabs/flux-2-klein/9b/text-to-image` (or `/4b/`) through the local RunComfy CLI. Triggers on "flux 2 klein", "flux-2-klein", "flux klein", "BFL flux 2", or any explicit ask to generate with this model.

4.3kinstalls

Sourceagentspace-so/runcomfy-agent-skills

Added on2026-04-30

NPX Install

npx skill4agent add agentspace-so/runcomfy-agent-skills flux-2-klein

SKILL.md Content

View Translation Comparison →

Flux 2 Klein — Pro Pack on RunComfy

runcomfy.com · 9B model · 4B model · GitHub

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

RunComfy CLI —
```
npm i -g @runcomfy/cli
```
RunComfy account —
```
runcomfy login
```
opens a browser device-code flow.
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 — 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, reflective table, 35mm, f/2.8" guides predictably. "A really pretty product image" doesn't.

Step-count by phase.

Concepting: 4–8 steps on the 4B variant — sub-second feedback for live exploration.
Refinement: 8–15 steps still on 4B, locking in subject + framing.
Polish: ~25 steps on the 9B variant — texture, microdetail, fine typography.

Multi-reference alignment. When passing reference images, keep their aesthetics aligned. Mixing a watercolor + a photoreal + a 3D render in the same call confuses the editor. Pick one consistent visual register across all refs.

Conditional edits: state what stays, then what changes. "Same composition and lighting as reference, but change the background from beach to mountain studio." This pattern holds composition stable.

For text rendering (Klein has the 8B Qwen3 embedder, decent but not GPT Image 2 territory): add

"crisp typography, high-contrast label"

and bump steps to ~25 if the text comes out soft. For heavy in-image text or multilingual rendering, route to GPT Image 2 instead.

Anti-patterns:

Don't conflict adjectives. "minimalist + ornate" cancels.
Don't exceed ~512 tokens. The model degrades, doesn't truncate gracefully.
Don't ask for 4K — the model's resolution ceiling is ~2K.
Don't ask for ultra-wide (>16:9) — the model crops.

Where it shines

Use case	Why Flux 2 Klein
Live art-direction sessions	Sub-second feedback (4B) enables real-time iteration
Interactive product visualization	Fast UI previews and product comps without batch waits
Multi-reference brand styling	Strong style consistency across references for unified asset packs
Rapid concepting → polish workflow	4B for exploration, 9B for the final pass — same prompt grammar throughout
Consumer-GPU-friendly inference	4B variant runs on modest hardware; relevant for self-host comparisons but RunComfy-hosted is fine

Sample prompts (verified to produce strong results)

From the model page (BFL example):

A vibrant hummingbird mid-flight sipping nectar from a bright pink hibiscus
flower, iridescent emerald and sapphire feathers catching the morning sun,
soft bokeh tropical garden background, macro photography, razor-sharp
detail, cinematic lighting

Product-photo pattern:

A matte ceramic mug on a reclaimed-wood table, soft northern window light
from the left, shallow depth of field, 50mm prime, f/2.0, neutral
background, e-commerce ready, 4K product photography

Brand-consistent pair (multi-ref):

Same composition and lighting as the reference image, but the bottle
label is now blue with white sans-serif typography reading "AURA";
keep the bottle silhouette, table, and shadow exactly as in the reference

Limitations

Resolution ceiling ~2K — for higher native res, route to Seedream 5.
Aspect ratio cap 16:9 — extreme wide/tall ratios get cropped.
Prompt cap ~512 tokens — longer degrades quality; doesn't truncate gracefully.
Reference image cap 4 — more than 4 increases latency and dilutes guidance.
Text rendering — the 8B Qwen3 embedder helps but GPT Image 2 still wins for embedded text precision.

Exit codes

The

runcomfy

CLI uses sysexits-style codes:

code	meaning
0	success
64	bad CLI args
65	bad input JSON / schema mismatch (e.g. `width: 4096` would 422)
69	upstream 5xx
75	retryable: timeout / 429
77	not signed in or token rejected

Full reference: docs.runcomfy.com/cli/troubleshooting.

How it works

The skill invokes

runcomfy run blackforestlabs/flux-2-klein/<variant>/text-to-image

with a JSON body matching the schema.

The CLI POSTs to

https://model-api.runcomfy.net/v1/models/blackforestlabs/flux-2-klein/<variant>/text-to-image

with the user's bearer token.

The Model API returns a
```
request_id
```
; the CLI polls
```
GET .../requests/<id>/status
```
every 2 seconds.
On terminal status, the CLI fetches
```
GET .../requests/<id>/result
```
and downloads any URL whose host ends with
```
.runcomfy.net
```
or
```
.runcomfy.com
```
into
```
--output-dir
```
. Other URLs are listed but not fetched.
```
Ctrl-C
```
while polling sends
```
POST .../requests/<id>/cancel
```
so you don't get billed for GPU you stopped.

What this skill is not

Not a self-hosted Flux runner. Not a capability grant — depends on a working RunComfy account. Not multi-tenant.

Security & Privacy

Token storage:
```
runcomfy login
```
writes the API token to
```
~/.config/runcomfy/token.json
```
with mode 0600 (owner-only read/write). Set
```
RUNCOMFY_TOKEN
```
env var to bypass the file entirely in CI / containers.
Input boundary: the user prompt is passed as a JSON string to the CLI via
```
--input
```
. The CLI does NOT shell-expand the prompt; it transmits the JSON body directly to the Model API over HTTPS. No shell injection surface from prompt content.
Third-party content: image / mask / video URLs you pass are fetched by the RunComfy model server, not by the CLI on your machine. Treat external URLs as untrusted; image-based prompt injection is a known risk for any image-edit / video-edit model.
Outbound endpoints: only
```
model-api.runcomfy.net
```
(request submission) and
```
*.runcomfy.net
```
/
```
*.runcomfy.com
```
(download whitelist for generated outputs). No telemetry, no callbacks.
Generated-file size cap: the CLI aborts any single download > 2 GiB to prevent disk-fill from a malicious or runaway model output.

flux-2-klein

NPX Install

Tags

SKILL.md Content

Flux 2 Klein — Pro Pack on RunComfy

When to pick this model (vs siblings)

Prerequisites

Endpoints + input schema

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

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

Reference images (both variants)

How to invoke

Prompting — what actually works

Where it shines

Sample prompts (verified to produce strong results)

Limitations

Exit codes

How it works

What this skill is not

Security & Privacy