[Bug] Image generation: CFG scale setting ignored in UI (always uses 1.0)

[eldesconectado]

Title: [BUG] CFG (Guidance) Scale Ignored in Image Generation and Always Uses 1.0 in v1.120

Problem Description

When generating images with KoboldCpp v1.120 (both koboldcpp.exe and koboldcpp-nocuda.exe), the CFG Scale (Guidance) value I enter in the web interface (/sdui) is completely ignored.

Generation always uses CFG Scale: 1.0, regardless of whether I enter 3.0, 6.0, or 9.0. This results in poor image quality, deformities in hands/legs, and, in my specific case, pubic hair, despite using very explicit negative prompts to remove it.

Steps to Reproduce the Error

1. Load the Flux model (fluxedUpFluxNSFW_71Q8GGUF.gguf) into KoboldCpp v1.120.

2. Open the image generation web interface (http://localhost:5001/sdui).

3. Enter a prompt and a negative. Set the Guidance (CFG) to 3.0 (or 9.0) and generate.

4. When finished, check the image metadata.

5. Result: The program reports CFG Scale: 1 (or CFG Scale: 1.0) instead of the value I entered.

Expected Behavior

The image metadata should reflect the CFG scale I configured (e.g., CFG Scale: 3.0). Additionally, the image should correctly follow the prompt and negative instructions with that guidance.

Tests performed (excluding common causes)

• I tested with CFG=3.0 and CFG=9.0 (even higher) and it always reports 1.0.

• I modified the "VAE Tiling Threshold" to 16 to force tiling, but the CFG failure persists.

• I tested both the normal .exe (606 MB) and the nocuda (113 MB), and the error occurs in both.

• I used exactly the same model, same seed, same prompt with sd-cli.exe (the separate stable-diffusion.cpp binary) and the CFG DOES work correctly there, which rules out a problem with the model or parameters. The bug is in KoboldCpp.

Environment

• Operating System: Windows 10 x64.
  Ryzen 9 5900XT, 32 GB RAN DDR4 -3200 MHz

• KoboldCpp version: v1.120 (released 3 days ago). I also suspect it occurs in earlier versions, but it's confirmed in the latest one.

• Executable file: koboldcpp.exe and koboldcpp-nocuda.exe.

• Model: fluxedUpFluxNSFW_71Q8GGUF.gguf (Flux.1 Dev).

• Backend: CPU (although it also occurs when selecting others).

Additional context

• The problem seems to be in how KoboldCpp passes the --cfg-scale parameter to the internal backend (stable-diffusion.cpp). It seems to always send 1.0.

Temporary Solution (for developers)

Review the communication between the web UI (/sdui) and the image generation core, specifically how the command or internal API call is constructed with the --cfg-scale flag.

Thank you for your work!

[LostRuins]

If you're using Flux 1.0, this is not a bug. Flux ONLY works with cfg 1.0. you could try using a different model like qwen image and cfg should work

[eldesconectado]

Hi, thanks for replying.

I understand that Flux base uses CFG=1.0, but the model I'm using is a fine-tune NSFW (fluxedUpFluxNSFW_71Q8GGUF) that I've tested with the sd-cli.exe binary (the same backend KoboldCpp uses), and with CFG=3.0 it works perfectly, and the negative prompt eliminates the hair I mentioned. In the CLI, the image metadata shows CFG Scale: 3.0.

The problem is that in KoboldCpp, even if I set CFG=3.0 (or 9.0, for example) in the UI, CFG Scale: 1.0 always appears in the generated image. This indicates that KoboldCpp is ignoring the value I'm passing it.

Is it possible that KoboldCpp is forcing CFG=1.0 for all Flux models? If so, is there any way to disable this behavior or pass extra arguments to the backend?

My request is that the user be allowed to force any CFG value they want, even for Flux models, or at least that the value I set in the interface not be overwritten. Not all Flux models are the base CFG; fine-tuned models may require CFG > 1.0.

Also, if possible, please indicate in the interface next to "Guidance" the term "CFG" in parentheses, "Guidance (CFG)", to make it clear that it refers to the same value.

I look forward to your response. Thank you.

[LostRuins]

Yes, indeed koboldcpp is forcing cfg 1.0 for flux, because it was observed that any other values resulted in garbage results.

See:
https://github.com/LostRuins/koboldcpp/blob/concedo/otherarch/sdcpp/sdtype_adapter.cpp#L1165-L1174

I will add a flag for you to disable this for advanced users.

[eldesconectado]

Excellent, that's exactly what I needed! I'm glad to hear you've identified the cause and are adding an option for advanced users. I wasn't aware that Flux Base behaved that way by default.

Thank you so much for your time and the entire team's. I'll be keeping an eye out for future versions to test it out.

Best regards, and thanks for the great work!

[LostRuins]

in 2 hours you can download the rolling build which has this fix https://github.com/LostRuins/koboldcpp/releases/tag/rolling

to enable it, pass {"remove_limits":1} into the gendefaults (default params) box.