[BUG] INSTRUCT mode stops suddenly: does not call tools in multi-turn agent loops

#5
by BebopVox - opened

Hi,
Thank you for your model! πŸ’Ÿ

I have a problem with INSTRUCT mode.


The problem below reproduces 11/Sep/2026 by myself. Investigation and text below is written with help of AI


Summary

The model ends its turn after a narrative intent sentence. It does not emit the promised tool call. This breaks multi-turn agentic tool loops. Enabling low-effort thinking fixes the problem.

Environment

Item Value
Llama-server build b10641, Vulkan backend
Docker image image: kyuz0/amd-strix-halo-toolboxes:vulkan-radv-performance
Hardware AMD Strix Halo, 64 GB unified memory
Quant Qwen3.8-27B-TTURBO-Fable-C-Fusion-709-L-Uncen-NM-DAU-NEO-Q4_K_M.gguf
Harness OpenAI-compatible chat completions with tools / or OMP (oh-my-pi) agent

Server flags:

--parallel 2
--temp 0.7
--top-p 0.80
--top-k 20
--presence-penalty 0.0
--repeat-last-n 0
--repeat-penalty 1.0

Chat-template-kwargs:

{"enable_thinking":false, "reasoning_effort":"xhigh", "preserve_thinking":true}

Observed symptom

The model calls the first tool correctly. The tool result returns. The model then writes a short sentence, for example:

"Let me also list files to demonstrate another tool:"

The turn ends. It emits no second tool call. Logs show stopReason:"stop", hasToolCalls:false, hasText:true.

The user must prompt again before the model continues. The model repeats this pattern when prompted to continue.

Reproduction

  1. Start a chat with tools available.
  2. Ask the model to demonstrate tool use.
  3. Let it call the first tool.
  4. Return one tool result.
  5. Observe the next turn.

Expected result: the model calls the next tool.

Actual result: the model narrates intent and stops.

Measured chain rate

Same two-turn reproduction run repeatedly:

Thinking mode Chained second tool Rate
Off (instruct, effort xhigh) 1 of 12 ~8%
Low 7 of 8 88%
Medium 8 of 8 100%

The failure is stochastic. The same configuration flips between success and failure between runs.

Root cause hypothesis

The TURBO fusion compresses reasoning tokens. In instruct mode there is no reasoning block at all. The model appears to plan the next tool call internally. The output generation then stops before it can emit the <tool_call>. This matches the issue reported on the TURBO-735 card in discussions #22 and #25.

Workaround that works

Set enable_thinking:true and reasoning_effort:low. The model then chains tools reliably at a modest reasoning-token cost.

Questions

  1. Is this expected or anyone faces this as well on INSTRUCT mode (not thinking)?
  2. Is reasoning_effort:low the recommended mode for agentic tool loops on TWIN-TURBO?

@BebopVox

thank you for your report and detailed testing/notes.

Try quant:
Q5KS/Q6 ; as tool calling (with instruct mode) will need the extra precision... you might even need Q8.

Hopefully this should help.

Tried both recommendations.
Still no success with Qwen3.8-27B-TTURBO-Fable-C-Fusion-709-L-Uncen-NM-DAU-NEO-Q6_K.gguf πŸ˜₯

image

I'll try Q8 later on.

BebopVox changed discussion title from [Bug] INSTRUCT mode stops after narration: does not call tools in multi-turn agent loops to [BUG] INSTRUCT mode stops suddenly: does not call tools in multi-turn agent loops

Q8 same problem
Qwen3.8-27B-TTURBO-Fable-C-Fusion-709-L-Uncen-NM-DAU-NEO-Q8_0.gguf

image

image

Do you have any ideas what am I doing wrong?
Or have you reproduced the same behavior?

I wanted to use instruct to make this model x2-x3 faster and remove thinking whatsoever.
Yes this model is cooking but dense 27B is still very slow on my hardware so Im looking for alternatives 😊

I have the same problem. Also tried multiple quantization and settings but it seems to be related to context length. As soon as I reach ~20K context it's a non stop failing. Never before.

I am also having exact same problem with llamacpp + opencode

DavidAU changed discussion status to closed

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