Text Encode with Flux2 Klein System Prompt (Scaled Bias)

Flux 2 Klein is the distilled little sibling that actually shipped - 9B/4B, runs on normal cards, became the default local editor for the first half of 2026. Its text encoder is a Qwen3-class chat model, which means it speaks the Qwen <|im_start|> template and has a <think> block you can feed reasoning into. UC_ScaledBiasTextEncodeKleinSystemPrompt exists to format your prompt exactly the way that encoder wants it.

The mechanism

The node builds a Qwen3-style chat template: system turn, user turn containing your prompt, then an assistant turn that opens a <think> block. Your system_prompt goes in the system slot, your prompt in the user slot, and thinking_content - the input the other variants don't have - gets injected as the reasoning text inside <think>. Leave it empty and the model uses its default thinking. Then the whole thing runs through the pack's scaled-bias encoder, so you can also emphasize words with the <word=1.5> syntax that works on Qwen tokenizers instead of the SD-style parentheses that get read as literal text.

Inputs: clip, prompt (multiline), system_prompt (multiline, default empty), and thinking_content (multiline, default empty - the tooltip says leave empty for the default). Output: one CONDITIONING socket for the sampler's positive/negative input.

Why the think block matters

Klein's encoder was trained to reason before it answers, and the <think> slot is where that reasoning lives. Filling it with a short chain-of-thought - "the scene is a rainy street at night, neon reflections on wet asphalt" - can push the model toward actually honoring the scene description instead of guessing. That's the kind of knob that separates "Klein understood my prompt" from "Klein painted a generic street." It's also the fastest way to experiment: type reasoning, see what changes, tweak, re-run.

Install

Part of ComfyUI-UtilsCollection:

cd ComfyUI/custom_nodes
git clone https://github.com/silveroxides/ComfyUI-UtilsCollection

Restart, or install via ComfyUI Manager (search "UtilsCollection"). No model downloads - you bring your own Klein CLIP.

Gotchas

Template discipline matters more here than anywhere else in this family: this is the Klein variant, so feed it a Klein CLIP, not a Flux 2 dev or Z-Image one - the wrappers are not interchangeable. The scaled-bias family is experimental, so don't be surprised if inputs shift between pack updates. And if you ever see the "clip input is invalid" error, the clip really is None - check that Load CLIP is actually wired before you blame the template.