Qwen3.8-Flash-Next Unsloth Dynamic v3.1 on NVMe: a local 30-task A/B

#93
by SkyIsNotGreen - opened

Hello,

I served unsloth/Qwen3.8-Flash-Next-GGUF:UD-Q2_K_XL on one workstation with:

  • 30 GB host RAM
  • 2 x 20 GB AMD GPUs, one of them driving the display
  • NVMe-backed Flash-Next weights

I did not set out to check Unsloth's internal benchmark claims. I wanted to know whether a Flash-Next quant of this class can be served usefully on a memory-constrained workstation with the sparse-expert and mmap path in Strata, and how it compares with a ternary-based Scion under the same harness.

UD-Q2_K_XL scored 30/30 (100%) and streamed 79.6 GB on the 2 x 20 GB box at about 10 effective tok/s. Scion's 60.17 GB ternary build scored 27/30 (90.0%) and ran about four times faster. The 74.28 GB Q2 bridge scored 28/30 (93.3%). This is a size and speed trade-off; I would not call it a Scion win.

Result

UD-Q2_K_XL through Strata:

Metric Value
Tasks 30
Accuracy 30/30 (100%)
Completion tokens 11,470
Wall time 1,127.4 s
Median and p95 per task 28.6 s and 67.8 s
Effective tokens/s 10.17
ms per completion token 98.3
finish_reason=length 0

Same 30-task split, 8192 context, 4096 cap, 3072 thinking budget, and answer_room on:

Arm Size Accuracy Tokens Wall Effective tok/s ms/tok
Unsloth UD-Q2_K_XL 79.6 GB 30/30 (100%) 11,470 1,127.4 s 10.17 98.3
Scion Q2 bridge* 74.28 GB 28/30 (93.3%) 33,578 791.9 s 42.4 23.6
Scion Q6_K 60.17 GB 27/30 (90.0%) 39,922 951.4 s 42.0 23.8

* The Q2 bridge is a Strata-compatible repack of the Scion Q6_K release, not an official Scion Q2 and not ISTA's GSQ-RCO Q2_0.

The Unsloth arm had no MTP or speculative drafter (--spec 2, no --mtp). The Scion arms used spec 4 and MTP, so the speed columns are not a pure engine comparison. The accuracy columns use the same task protocol.

Accuracy vs effective throughput for Unsloth UD-Q2_K_XL, Scion Q2 bridge, and Scion Q6_K

Accuracy vs effective throughput (completion tokens / wall time). Bubble area is file size.

Setup

  • Unsloth artifact: unsloth/Qwen3.8-Flash-Next-GGUF, UD-Q2_K_XL, four shards, 79.6 GB on disk. I checked all four SHA-256 hashes against the Hub.
  • Quant contents: mixed IQ2_XXS, IQ2_S, IQ3_XXS, and Q2_0 experts; Q8_0 and Q6_K body; IQ4_NL PLE table with 320,001,536 rows.
  • Pack: a local Strata tools/iq_pack.py --compat-bf16 pack. It is 1.5 GB of dense body, with 302 tensors served natively; the experts and PLE stay in the GGUF.
  • Engine: the local Strata fork and Flash-Next config, two AMD GPUs, PLE and n-gram table disk-backed, --mmap-experts, --prefill 4096, --spec 2, --vram-reserve-mib 6144, --vram-reserve-later-mib 1024, --pool-workers 15.
  • Harness: the same 30-task split and checkers used for the Scion rows above.
  • Token budget: max_tokens=4096, thinking_budget_tokens=3072, answer_room on.
  • temperature=0.1, one sample per task, no thinking-preservation, raw OpenAI-compatible chat completions.
  • The task prompts ask for direct answers and final-answer markers. This is a local A/B benchmark, not a re-implementation of Unsloth's methodology.

How it ran

  • The Flash-Next PLE and n-gram table stays on disk instead of being duplicated into RAM.
  • Expert banks are read from the GGUF shards. The pack does not need a full copy of the model.
  • Strata's expert cache keeps hot expert banks in VRAM. The 79.6 GB model ran on 40 GB of VRAM plus the 30 GB host, with the rest read from NVMe.
  • The local pack conversion is not bit-identical to stock llama.cpp or Strata builds that read the file natively. 291 small non-native tensors were converted to the engine's form with --compat-bf16 and nearest-even rounding: 96 exact, 195 rounded, maximum absolute error 0.0154. The conversions are logged in compat-bf16.json and conversions.json.

Streaming

  • Average decode was 12.09 tok/s and average prompt was 44.09 tok/s on the 2 x 20 GB box. On the same box, the 60.17 GB Scion Q6_K ran at about 42 effective tok/s, roughly four times the throughput.
  • The 30-task run took 1,127 s end to end with 11,470 completion tokens. Decode waited on disk, which is the cost of streaming the 79.6 GB file.

Accuracy by benchmark, per-task latency distributions, and total completion tokens

Accuracy by benchmark, every task's wall time, and total completion tokens.

Caveats

  • I ran one server arm at a time. Both GPUs are used by the layer split, and the setup is not tuned for maximum throughput.
  • This is not a comparison against Unsloth's published long-thinking 256k-context benchmarks.
  • This is not one of Unsloth's recommended xhigh reasoning runs. It is a one-sample, low-temperature matrix meant to expose code, reasoning, and QA failures.
  • The Unsloth arm ran without MTP or speculation; the Scion arms used spec 4 and MTP. Speed is not apples-to-apples.
  • The Scion and Unsloth arms used different VRAM reserves (3072 and 6144) and expert-cache placements. The 30-task suite is small and cache-sensitive.
  • The pack build rounds small tensors. Do not quote it as a stock or official production benchmark.
  • One 30-task run is not frontier capability evidence.
  • The download is large enough that normal machines will not run this casually. The question here is whether this tool lets a Flash-Next-scale model run usefully on constrained hardware.

Reproduction

  • Harness: hivebench/experiments/ab_qwen27_flashnext.py and hivebench/experiments/model_matrix.py in sky-is-green/hive
  • Test split: hivebench/experiments/cascade/tasks-bench.json
  • Raw data: hivebench/experiments/model-matrix/ab-unsloth-flashnext-ud-q2k-xl-4096-tb3072.json, ab-scion-q6k-v0210-4096-tb3072.json, ab-scion-q2-v0210-4096-tb3072.json
  • Unsloth config and stack: hivebench/stacks/strata/configs/unsloth-flashnext-ud-q2_k_xl.json, hivebench/stacks/unsloth-flashnext-strata.json
  • Pack conversion logs: compat-bf16.json and conversions.json beside the pack. The SHA-256 hashes for all four shards were verified against the Hub.

Why I'm posting this

I'm posting this because it's a concrete example of Flash-Next-scale inference on hardware that does not hold the full model in RAM. The PLE table and expert pages stay on disk, hot experts go to vRAM, and the same task harness shows whether the local implementation produces useful outputs. On this 30-task matrix the Unsloth quant wins on accuracy. Scion's value is that it reaches 90% at 60 GB and roughly four times the throughput of the streamed 79.6 GB model. Both are constrained-hardware results, not contradictions of the model's high-end serving behavior.

License and attribution

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