Qwen3.8-Flash-Next REAP-320 "multi-domain" — GGUF

The successor to REAP-256 "duo": 512 → 320 experts per layer, 83.8 → 64.2 GiB (64.2 GiB = 68.96 GB decimal — the number HF's file listing shows; every size on this card is GiB, the same convention the compared models use), calibrated on a multi-domain corpus instead of code-only. Built directly in response to this community critique — the full head-to-head against Unsloth's UD-IQ1_M, including where this build loses, is published in that thread.

Not an official Qwen release. Community derivative, unaffiliated with Alibaba/Qwen.

Why K=320 and why multi-domain

• K=320 sits above the reliability knee. Two independent measurements (sh0wie's REAP ladder, and our own K=256 lineage) show rare-token reliability and clean termination degrading below ~K=288-320. At K=320: zero empty-content stalls and zero truncation across all our battery passes, 9/10 on the seeded rare-name probe.
• Calibration is the product. Salience was measured with llama-imatrix over a 525K-token corpus: 30% agentic / 30% code / 15% conversation / 12.5% math / 12.5% writing. The multi-domain build beat the code-only specialist even at code (HumanEval 96.3% vs 95.7%), and we have since reproduced the effect at K=256, where changing only the corpus moved HumanEval from 89.6% to 95.1% at identical size and identical bits.

Correction (2026-09-01). An earlier version of this card claimed this selection "retains 82.7% of routing mass vs 75.3% for a code-only selection at the same K." That number is withdrawn. It was measured against a corpus drawn from the same mixture that produced this selection, and the metric turns out to be circular — each selection wins when scored against the corpus that produced it. We then ran it as a genuine prediction on a K=256 rebuild: retained routing mass said the new selection would be worse (82.7% vs 78.0% for the incumbent), and every behavioural probe said the opposite, decisively. Retained routing mass is useful for understanding a prune; it does not rank two prunes. The HumanEval, rare-name and fabrication numbers below are unaffected — those are measured on the model, not on the selection.

⚠️ Throughput figures in the tables below are superseded. They have been corrected twice — once for a protocol error and once for a bug in the correction itself. Read Corrections to this repository at the bottom before citing any tok/s number from this card. Quality figures (HumanEval, rare-name, fabrication) are unaffected throughout.

Measured (all on RTX 5090 32 GB, llama.cpp + expert-cache PR #27861 build)

Honest limitation, stated loudly: pruning experts costs world knowledge. On our 12-question fabrication probe this build fabricates 25% (the old K=256 duo: 42%; unpruned UD-IQ1_M: 0%). If you want a general-purpose assistant, take Unsloth's UD-IQ1_M — experts store knowledge, bits store precision. Take this build when fit and speed in constrained VRAM dominate: it is 5 GiB smaller than the 1-bit route, prefills ~23% faster under the same cache regime, and generates concisely.

New: Q2 variant — same experts, fewer bits, fully GPU-resident on 32 GB

Q2/ holds a second quant of the same K=320 selection (same manifest, same imatrix), pruned by binary copy from Unsloth's UD-Q2_K_XL: 2 shards, 57.3 GiB (61.5 GB decimal). That is the same disk footprint as the legacy K=256 duo at Q3 (57.7 GiB) — which makes it a controlled bits-vs-experts comparison at constant size:

At equal disk, 64 extra experts per layer beat 1 extra bit per weight on every knowledge metric, and cost only 1.2 HumanEval points vs the Q3 build while freeing 7 GiB — enough to make the whole compute path GPU-resident on a 32 GB card. Recommended residency: --n-cpu-moe 3 (leaves ~2 GiB VRAM margin; --n-cpu-moe 0 measures faster but runs the card at ~98% and risks driver timeouts under load).

Files

Main quant: UD-Q3_K_XL-lineage (pruned by binary copy from Unsloth's quant — surviving experts keep their original bits, no requantization). 2 shards, 64.2 GiB (68.96 GB) total. Plus the Q2/ variant above: 2 shards, 57.3 GiB (61.5 GB).

manifests/seleccion_mass_K320.json ships the per-layer kept-expert manifest ({"<layer>": [expert ids...]}, stock ids 0-511) — the prune is reproducible from the source quant, and the manifest is directly usable by SSD-expert-streaming runtimes as a pinned set.

Run it

Needs llama.cpp mainline ≥ 2026-08-27 (PR #27742, qwen4exp support):

llama-server -m Qwen3.8-Flash-Next-UD-Q3_K_XL-reap320-00001-of-00002.gguf \
  -ngl 99 --cpu-moe -c 32768 -fa on --jinja --parallel 1 \
  --temp 1.0 --top-p 0.95 --top-k 20 --min-p 0.0

On a 32 GB card, add the expert-cache from PR #27861 (--moe-expert-cache 128) for ~42-45 tok/s decode. Set reasoning effort explicitly ("chat_template_kwargs": {"reasoning_effort": "low"}) — the template defaults to xhigh and replies take minutes.

For the Q2/ variant on a 32 GB card, skip the cache entirely and run near-resident — this is the fast path (86.9 tok/s decode, ~1000 tok/s prefill):

llama-server -m Q2/Qwen3.8-Flash-Next-UD-Q2_K_XL-reap320-00001-of-00002.gguf \
  -ngl 99 --n-cpu-moe 3 -c 32768 -fa on --jinja --parallel 1 \
  --temp 1.0 --top-p 0.95 --top-k 20 --min-p 0.0

New: run the Q2 with Unsloth's MTP head (+32% decode, costs 3.2 GiB)

Unsloth published standalone MTP heads for Qwen3.8-Flash-Next on 2026-09-01. They work on this pruned Q2 build — the head is not affected by expert pruning — and are the single biggest speed lever we have found for it. Measured on the same 32 GB card, same GGUF, same flags, paired:

Draft acceptance is 76–81% (mean accepted length 2.5–2.6). Quality is preserved: HumanEval-164 94.5% with MTP vs 95.1% without — Unsloth's verification is exact, and the one-problem gap is sampling noise.

# Needs a build with the Flash-Next MTP graph, NOT stock mainline (see "Which build" below and trap 4)
llama-server -m Q2/Qwen3.8-Flash-Next-UD-Q2_K_XL-reap320-00001-of-00002.gguf \
  -md mtp-Qwen3.8-Flash-Next-shared-Q8_0.gguf \
  --spec-type draft-mtp --spec-draft-n-max 2 \
  -ngl 99 --n-cpu-moe 8 -c 65536 -fa on --jinja --parallel 1 \
  --cache-type-k q4_0 --cache-type-v q4_0 \
  --temp 1.0 --top-p 0.95 --top-k 20 --min-p 0.0

Which build. Stock llama.cpp mainline has the --spec-type draft-mtp flag but not the Qwen3.8-Flash-Next MTP graph, and not the loader that lets the shared heads borrow token_embd / output from the main model. Any of these three works (same list as Unsloth's MTP/README.md):

1. Unsloth's fork, release tag b10715-mix-86bd2d3 or newer — https://github.com/unslothai/llama.cpp/releases. The prebuilt binaries there are CUDA and CPU only. For ROCm (and for Windows) take the source tarball of that tag and build it exactly like you build mainline (-DGGML_HIP=ON etc.). This repository's numbers come from a b10798-mix source build on Windows/CUDA.
2. Upstream PR https://github.com/ggml-org/llama.cpp/pull/28243 (the same code on its way to mainline; still a draft as of 2026-09-09).
3. Unsloth fork PR #144.

On a correct build the shared head prints one error line at startup about borrowing the embeddings. That line is normal; it works. The shared-Q4_K_M head (1.78 GiB) saves another ~840 MiB of VRAM versus shared-Q8_0 at the same acceptance (0.70 vs 0.72 measured), useful on 24 GB cards.

The head costs ~3.2 GiB of VRAM, flat — the same at every offload level we tried (--n-cpu-moe 14 / 12 / 10 / 8), so budget for it once. On a 32 GB card at 96k context, --n-cpu-moe 10 is the balanced point (30578 MiB, 93.8%, 92.5 tok/s); 8 is the fast one but leaves under 1 GiB free.

A note on how we measured this, because we got it wrong first. Our initial harness reported 369 tok/s for this configuration — a 3.6× speedup. It was wrong. It timestamped only stream chunks carrying content, while this model emits its reasoning in reasoning_content; that time landed in "time to first token" while its tokens stayed in the numerator. The inflation scales with how much the model reasons, so it was invisible on a short prompt and enormous on a long one. The +32% above is wall-clock, cross-checked against the server's own predicted_per_second. If you benchmark a reasoning model, make sure your timer sees the reasoning stream — and require two independent clocks to agree before you believe a number.

New (2026-09-06): prefill — the PLE table is why your prompt speed swings 3×, and --lazy-mode on-direct fixes it

Flash-Next carries a 26.8 GiB per-layer-embedding table (per_layer_token_embd.weight, 320M rows × 90 B) that is untouched by expert pruning and stays on the host. llama.cpp reads it through mmap: one page fault per ~90-byte row, on every token of the prompt. Whether those pages are in the OS cache decides your prefill speed — and on a machine that also loads other 20–60 GB models, they usually are not. Our production log showed 245–2652 tok/s on 11–25k-token prompts for exactly this reason, and repetitive benchmark prompts (few distinct rows) hide it completely.

PR #28136 adds --lazy-mode on-direct: positioned reads from a worker pool instead of demand faults. Measured on the Q2/ build (RTX 5090, Windows 11, 95 GB RAM, NVMe) with a genuinely cold cache (RAMMap -Et + fresh process per arm), a real 25k-token mixed prose+code prompt, cache_prompt: false, two cycles:

on-direct is the one that gives the same number every time; off is fast while the resident table survives but loses it whenever Windows trims the working set. With Unsloth's MTP head loaded (same protocol): 259 → 506 cold, 404 → 604 on new rows, decode unchanged (72 tok/s). A 28k-token prompt now prefills cold in 44 s instead of 74–152 s.

To use it today: the PR is still open, it is POSIX-only as written (Windows prints --lazy-mode on-direct is not supported on this platform and silently falls back to mmap — you need this Windows port from the PR thread), and the prebuilt Unsloth binaries reject the value. We build Unsloth's b10798 mix source + the PR + the Windows port, which keeps the MTP head working. Full numbers, including the Windows-native table, are in the PR thread. If you cannot build: --lazy-mode off (mainline and Unsloth builds accept it) gets most of the cold gain for 26.8 GiB of RAM.

Traps (measured, not theoretical)

1. --parallel > 1 requires --kv-unified.
2. Empty content with tight max_tokens: reasoning burns the budget. Detect and retry with a higher cap.
3. First requests after a cold load pay disk; throughput climbs over ~3-4 requests to its warm ceiling. The disk cost is the PLE table (see the prefill section above); --lazy-mode on-direct removes it.
4. --spec-type draft-mtp exists in llama.cpp mainline but does not work here. Mainline has the flag and not the MTP graph for qwen4exp, nor the tensor borrowing the shared heads need. Symptoms on mainline: with a shared-* head, tensor 'token_embd.weight' not found → failed to load draft model (the head omits the embeddings on purpose, it is not a corrupt download); with a fused model, model doesn't contain MTP layers. The non-shared head is not a workaround: it gets past the missing tensor and fails later for the same reason. Use one of the builds listed under "Which build" above (ROCm users: build the Unsloth tag from source).
5. "reasoning_effort": "none" returns HTTP 500 — the chat template accepts only xhigh / medium / low.

Credits

• Qwen for Qwen3.8-Flash-Next (Qwen Community License 1.0).
• Unsloth for the UD-Q3_K_XL quant this was pruned from, and for UD-IQ1_M, the honest benchmark opponent.
• Cerebras Research for the REAP method.
• sh0wie for independently mapping the pruning-reliability knee and publishing saliency manifests.
• The critic in discussion #2, whose pushback made this model exist.

---

Corrections to this repository

2026-08-31 — every throughput number in this card was measured with a flawed protocol, and the context they were measured at was not stated. Both are corrected below. One correction favours this build; the other does not.

What was wrong

1. The decode rate included prefill. Throughput was computed as total wall time ÷ output tokens. That folds time-to-first-token into what was reported as a decode rate, so every decode figure in this card was too low. The corrected protocol streams the response and measures only the interval between the first and last token, with ignore_eos forcing a fixed output length so the sample size cannot vary. Protocol borrowed from jpezzulli/pennyroyal-validation.

Note for anyone reproducing this: llama-server's own timings.predicted_per_second tracks the old, prefill-contaminated figure, not the post-first-token decode rate. Do not use it.

2. The numbers were measured at 8,192-token context, and this card recommends a configuration that collapses at the context it is served at. The context was never stated. For the --n-cpu-moe 4 configuration this turns out not to matter — 94.37 tok/s at 8k versus 93.45 at 98,304, inside noise. But for the --n-cpu-moe 0 "fast path" this card recommends, it matters enormously, and not in the way a reader would be able to detect:

It does not fail. It loads, it answers, and it runs 10.7× slower. At 98.7% of a 32 GB card the driver begins paging and throughput collapses silently. The only trace is one warning that says nothing about the consequence:

common_fit_params: failed to fit params to free device memory: n_gpu_layers already set by user to 99, abort

This card already warned that --n-cpu-moe 0 "runs the card at ~98% and risks driver timeouts under load", and recommended --n-cpu-moe 3 instead. That warning was directionally right and mechanically wrong, in a way that makes it easy to ignore:

• it said "under load" — this happens at one concurrent request, with nothing else on the card;
• it said "driver timeouts" — there is no timeout. Nothing errors. It just gets 10.7× slower;
• it gave no magnitude, so "risks timeouts" reads like an edge case rather than a 10× cliff.

Do not run --n-cpu-moe 0 at long context on a 32 GB card. Use --n-cpu-moe 4: it is slower at short context and it is the only one measured here that holds its throughput at 98,304.

Corrected table

All figures: post-first-token decode, ignore_eos with 1,024 forced output tokens, temperature 1.0 / top-p 0.95 / top-k 20 / min-p 0.0, reasoning_effort: low, warm-up pass discarded, single RTX 5090 (32 GB) with no other process on the GPU.

Two prompts are reported because they differ a lot on this build: a prose prompt written to force continuously distinct output (which suppresses n-gram draft hits), and a code prompt (where the n-gram drafter earns its keep).

Q3 main quant (UD-Q3_K_XL-lineage, 64.2 GiB), same protocol. Note this build is served without speculative decoding, where the Q2 rows above carry --spec-type ngram-map-k4v:

An earlier independent run of the --n-cpu-moe 4 / 98,304 row two hours before this sweep gave 94.61 / 127.47 — 1.2% from the figure above, which is the reproducibility this protocol delivers.

Two things the corrected numbers show that the old ones hid

The expert cache is not the slow option — it is the option that holds. At 8,192 tokens --n-cpu-moe 0 beats the cache almost 2:1 (116.14 vs 58.46). At the 98,304 this build is served at, the cache is 6.5× faster (70.52 vs 10.82), because it leaves ~10 GB of headroom instead of running the card at 98.7%. The original table presents the cache as the bottom rung. At real context it is the top one.

--cache-reuse speeds up decode, not just prefill. --moe-expert-cache 192 --cache-reuse 256 against --moe-expert-cache 128 alone: +15% prose, +23% code, both at 98,304. It was adopted here for time-to-first-token; the generation gain was not measured until now. If you run the expert cache, run it with --cache-reuse.

What this does and does not change

Nothing about the weights changed. No re-quantisation, no re-prune. This is a measurement correction and a disclosure of a condition that should have been in the table from the start.

The quality claims in this card are unaffected and unretracted: 95.1% HumanEval, 9/10, and the 25% fabrication rate on the 12-question probe stand as published. The trade this build makes — experts store knowledge, bits store precision — is not a throughput claim and does not move.

If you are choosing between this and Unsloth's UD-IQ1_M, the corrected numbers do not change that advice. That build fabricates 0% where this one fabricates 25%. Take this one when fit and speed in constrained VRAM dominate; take theirs when you want general knowledge.

---

2026-09-01 — the correction above was itself measured wrong. The throughput numbers in it are inflated; the advice it gives about predicted_per_second is backwards. The --n-cpu-moe 0 collapse it documents is real and stands.

The bug in our corrected harness

The 2026-08-31 protocol streams the response and measures the interval between the first and last token. It timestamps a chunk only when that chunk carries content:

delta = (ch.get("delta") or {}).get("content")
if delta:
    if first_at is None: first_at = now
    last_at = now
...
ct = usage["completion_tokens"]              # ALL tokens, reasoning included
decode_tps = (ct - 1) / (last_at - first_at) # window of content only

This model emits its chain of thought in reasoning_content, a different field of the delta. Those chunks are never timestamped, so the entire reasoning phase falls inside what the harness calls "time to first token" — while its tokens remain in the numerator. The numerator counts reasoning; the denominator excludes the time that produced it.

The inflation scales with how much the model reasons, which is why it was invisible to us: our prose prompt reasons briefly and our code prompt reasons at length, and we read the resulting gap as a code-versus-prose effect. It was not. It was the same server.

For the row this build is actually served at — --n-cpu-moe 4, 98,304 context, code prompt — we published 126.95 tok/s. Measured by wall clock: 85.0 tok/s.

And so: predicted_per_second is fine. Please disregard our warning about it.

The 2026-08-31 note told you that llama-server's timings.predicted_per_second reports a "prefill-contaminated" figure and to not use it. That is wrong. Re-measured today, that counter agreed with wall-clock throughput to within 3% on every configuration we tried. It was our harness that disagreed with reality, not the server.

The rule we should have followed, and now do: a throughput number needs two independent clocks that agree. We report three — wall clock, post-first-token decode, and the server's own counter — and treat any disagreement beyond ~10% as a measurement bug rather than a finding. Had we done that in August, the harness would have failed its first run: it printed old method: 94.71 next to decode: 369.09 and we read that as the old method having been too conservative.

What survives and what does not

Survives. The --n-cpu-moe 0 collapse at long context — 10.7× is far too large to be a metric artifact, and it reproduces in every clock. Do not run --n-cpu-moe 0 at 98,304 on a 32 GB card. The relative ordering within a single prompt and a single speculation setting is also roughly preserved, since the inflation factor is common to those rows: the expert cache really does overtake --n-cpu-moe 0 at long context, and --cache-reuse really does help decode and not only prefill.

Does not survive. Every absolute tok/s figure in the 2026-08-31 table — inflated by roughly 1.5× on the code prompt and less on prose. And any comparison across rows that differ in speculation setting, including the Q3-without-spec against Q2-with-spec table, because those rows produce different reasoning-to-content ratios and the inflation no longer cancels.

Unaffected, again. No weights changed. The quality claims — 95.1% HumanEval, 9/10 on the rare-name probe, 25% fabrication — are measured by counting correct answers, not by timing, and do not move.

We are not republishing a full corrected table here until it has been re-run end to end with the three-clock protocol. The honest anchor in the meantime: as served (--n-cpu-moe 4, --spec-type ngram-map-k4v, 98,304 context, KV q4_0), this build generates 85 tok/s wall-clock on a code prompt, and the MTP configuration described above raises that to roughly 92-97 depending on offload.

Two measurement corrections in two days, the second one correcting the first. The lesson we are taking from it: a fix to a measurement does not validate itself. It has to be reconciled against the method it replaces, and a large unexplained improvement in your own numbers is a symptom before it is a result.