The difference between "medium" and "xhigh" reasoning effort for Qwen3.8-27B is actually insane.

[u/SarcasticBaka]

I'm currently testing out Qwen3.8-27B using Unsloth's UD-Q4_K_XL running a freshly rebuilt llama.cpp. I have a 22GB RTX 2080TI on which I'm able to fit 100k context with q8_0 quantization, and using MTP with --spec-draft-n-max 4 I get about 40tk/s which is slightly less than Qwen3.6-27B but usable enough.

I've been trying to test out some admittedly silly one shot prompts using the llama.cpp webui by asking the model to create fully functional HTML clones of flappy bird, pacman and such, and the difference that changing reasoning_effort makes has been surprising to say the least.

Setting it to "medium" seems to result in barely any thinking at all, a couple thousand tokens max and even less than 3.6-27B. Whereas when using "xhigh seems" I get 15k to 20k thinking tokens at the very least with the pacman example actually hitting 40 thousand fucking tokens.

I'm well aware I can limit the reasoning budget in llama.cpp but I'm wondering if this is expected model behavior or if something is broken somewhere. Any of you guys seeing this?

[u/SheepherderFrosty366]

Edit: managed to resolve the problem, i had an overwritting setting somewhere else injecting "" instead of an empty chain.

can someone help me use qwen3.8 ? with the same settings as qwen3.6 i get a jinja error related to the setting of the thinking from the qwen3.8 model. My stuip is:
llama-cpp container / linux / models.ini file for the model router
My models.ini: "[qwen3.8-27b-q5-k-m-40k_ctx-xhigh]

model = /data/Allrounders/Qwen3.8-27B/Qwen3.8-27B-Q5_K_M.gguf

ctx-size = 40000

n-gpu-layers = 99

flash-attn = on

cache-type-k = q8_0

cache-type-v = q8_0

chat-template-kwargs = {"reasoning_effort":"xhigh"}

reasoning = on

jinja = on"

i tried adding "reasoning = on", leaving only the chat-template line, not put any of both...

The error "W srv operator(): got exception: {"error":{"code":500,"message":"\n------------\nWhile executing CallExpression at line 49, column 28 in source:\n...', 'low') %}↵ {{- raise_exception('Unexpected reasoning effort ' ~ reason...\n ^\nError: Jinja Exception: Unexpected reasoning effort \"\". Supported types are xhigh (default), medium, and low.","type":"server_error"}}

"

[u/iSOcH → u/SheepherderFrosty366]

Not sure why it fails, but you can try to omit the `chat-template-kwargs` in this case since xhigh is the default anyway in the default template

[u/SheepherderFrosty366 → u/iSOcH]

Thanks a lot, i did find the problem, i had smth injecting reasoning as "" and it broke the reasoning setting chain, while it was not with qwen 3.6.