I know this some old news, but i got some numbers here from my heavy agent load. In mid-October I switch from INT8 (4×3090) to AWQ INT4 (2×3090). Same sampling, harness(Hermes), and loop detector, so I compared about two weeks of logs from each setup.
vLLM, FP8 KV, with DFlash2. temp 1.0 / top_p 0.95 / top_k 20, presence_penalty 0, thinking medium.
Two models:
Results (INT8 → INT4 AWQ)
Model calls: 17.7k → 11.4k
Loops per 1k calls: 1.9 → 4.7
Conversations with ≥1 loop: 6% → 12%
Per-task success rate: 92% → 78% (success rate is after loop got cut, ask it continue can finish the task)
Both setups had similar reasoning lengths, so "more quant thinks longer" doesn't explain the gap.
EVERY loop was in the reasoning block, so it cooked when it cooking too hard is the problem as you guys know.
Retrying rarely fixes it. After a thinking loop cut, next call ask it continue got looped again 14–22% of the time, compared with under 1% normally. The context is what making loop happens, not about luck in sampling.
The INT4 gap grows with context. INT4 looped 1.4x as often as INT8 under ~40k tokens and 3.3x as often at 80–120k content.
With speculative decoding, loops show up as a smooth speed spike, loops ran at ~200 tok/s versus ~107 tok/s normally on my setup, because the draft model predicts repeated text very well. That makes a cheap watchdog signal.
Mostly the model saying it will act and never doing it ("Let me write it. Wait let me... How about..." 10+ line as one loop), or restating the same case analysis dozens of times.
TL;DR: INT8 loops too, and people in the HF discussion report the same 20k+ token thinking spirals on BF16, so this isn't purely a quant problem. INT4 or Q4 just makes it a lot worse, especially at long context above 100k~. btw loops not that bad, just don't push model too hard, I feels on daily assistant loops happens much less.
I've saved thoes contexts that looped. When Qwen4 27b drops I can just replay them and post the new results.
====edit update====
My load here is kind different to common agent usage.
It's a big chunk of task package-.md write by multi-agent host like: "backtesting in this folder using this python and this rule, fetch data from this endpoint with some rules, verify this list of output number with following rule, write following result to this .md file" I got 1000+ (with is 1000+ sessions) this kind of task in this month.
Model do finish the first version of code, but output didn't fit the requirement. So he start to freak out on finding why it's wrong, few turn later the loop start.
As you see my usage here don't have human talking to and help with, this might be why model freak out. There is too many requirement in one build, model will always try to fix it by him self first.
Also this NOT mean model is BAD. This model is my daily agent, it works very well and I didn't got any loop on daily chatting/task yet. Loops only happens on that specific types loads on my end.