Qwen3.8-Flash-Next — APEX GGUF

GGUF conversions of Qwen/Qwen3.8-Flash-Next — a 180 B-total / ~6.8 B-active multimodal MoE (48 layers, 512 routed experts, top-10 routing, hybrid gated-delta-net with full attention every 4th layer, QSA sparse attention, per-layer n-gram embeddings, 262 K context).

Two files are usable directly: MIDDLE for inference, BF16 as a quantization source.

Files

The BF16 is a lossless conversion of the tensors it contains: the checkpoint is already bfloat16 on disk (config.json → "dtype": "bfloat16"), so the GGUF holds identical bit patterns. There is no reason to run it for inference.

llama.cpp compatibility

qwen4exp is in mainline. PR #27742 merged 2026-08-27 — about nine hours after these files were first published — followed by #27880, #28023, #28123 and #27941.

Verified against a stock, unpatched build (b2276-22397c31a, 2026-09-09) rather than inferred from the merge: the published MIDDLE file loads and generates correctly, and --parallel 4 served four concurrent requests without the indexer/attention cache assert that the pre-merge build hit. Perplexity below was measured on that same stock build.

If your build predates the merge, use brywil/llama.cpp @ qwen4exp-pr27742-spill-fix.

Converting this model yourself still needs that fork. The converter has to spill large tensors to disk and dequantize them in row bands instead of materialising them whole; without that it cannot produce these files at all. That fix is not upstream. Running the published files does not need it.

Running it

MIDDLE needs ~85.4 GiB resident for weights, plus KV cache and compute buffers.

llama-server \
  --model qwen3.8-flash-next-MIDDLE.gguf \
  --mmproj qwen3.8-flash-next-mmproj-F16.gguf \
  -ngl 999 -fa on -c 131072 \
  --parallel 1 \
  --cache-type-k f16 --cache-type-v f16 \
  -b 4096 -ub 2048 \
  --jinja --temp 1.0 --top-k 20 --top-p 0.95 --min-p 0

Three of those flags are not tuning choices:

• --parallel 1. The QSA sparse-attention indexer keeps its own KV cache alongside the attention cache, and multi-slot serving can desync the two. Serving with the default 4 slots aborted a benchmark run at task 2 of 9 on GGML_ASSERT(mctx_idx->get_n_kv() == inp->mctx->get_attn()->get_n_kv()).
• f16 KV only. q8_0 KV crashes or emits garbage on this architecture.
• Vendor sampling. temp 1.0 / top_k 20 / top_p 0.95 / min_p 0 is this checkpoint's own generation_config.json default. Substituting another model's numbers (an 0.6 carried over from an unrelated card) made a whole benchmark run incomparable.

KV cache is cheap here — only 12 of the 48 layers are full attention (2 KV heads, head_dim 256), so 24 KiB/token: 3.0 GiB at 131072, 6.0 GiB at the full 262144. The 36 gated-delta-net layers hold a constant-size recurrent state instead. Note that the indexer maintains a second cache of its own, so trust measured resident size over a hand-computed figure.

Measured

DGX Spark (GB10), stock llama.cpp b2276-22397c31a, MIDDLE, f16 KV, single slot:

Under matched flags (8192 ctx, f16 KV, single slot, same prompt and seed), generation measured 31.1 t/s on the stock mainline build against 28.3 t/s on the pre-merge fork build.

Vision

MIDDLE plus qwen3.8-flash-next-mmproj-F16.gguf, stock llama.cpp, five perception tasks put to the server directly (read a placard, transcribe a handwritten spec, name a function and its buggy line from a screenshot, read a value off a bar chart, count shapes):

The second row is the control: every answer is unguessable by construction, so a blind pass would mean the task was measuring text priors rather than the projector. None passed blind.

Note the sampling requirement this exposed: this model's chat template accepts reasoning effort xhigh, medium or low and raises on high, returning HTTP 500 for every request. A harness defaulting to high gets a 100% failure rate from a model that loads perfectly.

Agentic coding

MIDDLE on the frontier tier of an agentic coding suite (9 tasks, real tool-use loop, graded by a fresh pytest run), one run, DGX Spark (GB10), stock llama.cpp, --reasoning medium, 65536 ctx, single slot:

Per task: backtracking_regex 59 of 59 tests (5,552 output tokens), btree_insert_delete 14 of 14 (23,361), lru_ttl_cache 12 of 12 (1,724), mini_sql_executor 14 of 14 (1,911), or_set_crdt 9 of 9 (1,616), rate_limiter_fix_and_extend 8 of 8 (1,738), tiered_rate_limiter 6 of 6 (1,115), txn_kv_store 12 of 12 (1,557), weighted_interval_scheduling 8 of 8 (1,284).

A clean sweep on this tier is a floor rather than a ranking: the suite is built so that a competent coder clears it, and once it saturates the discriminating measurement is output tokens at equal score, which needs several runs per configuration. This is one run.

Perplexity

Not quoted here yet. A wikitext-2 run on this box returned 4.2801 +/- 0.02495 (--ctx-size 2048 --chunks 145 --seed 1234), but the corpus file used has sha256 aca2f467... and is not the canonical wikitext-2-raw-v1 release artifact (173c87a5...). n_chunk is a function of tokenised byte count, so a different copy of the corpus changes the divisor; the figure is therefore not comparable to perplexities published for other builds of this model, and is left out rather than shown next to them. It will be restored once measured against the release artifact.

What MIDDLE actually contains

Measured by reading the published file's tensor index — 1224 tensors, 176.944 B parameters, 91,655,638,816 bytes, 4.144 bpw.

The two big Q4_0 blocks are not a recipe preference — see the shape constraint below.

Not included: the MTP head

MIDDLE and BF16 are backbone-only. Two blocks of the 180.000 B are absent:

That leaves 176.944 B. The MTP head is a 1-layer multi-token-prediction block for speculative decoding; the converter sets supports_mtp_export = False for this architecture and discards its 31 tensors silently — no warning appears in the conversion log. --mtp is refused outright (--mtp / --no-nextn are not supported for Qwen4ExpForConditionalGeneration). The closed PR #27739 implemented both the export and the runtime graph, and its author deferred to #27742 with the intent that the useful parts be reconciled — so this is a scope cut, not a limitation of the format.

If you need the MTP head, or full-model reproducibility, start from the original safetensors, not from these files.

Notes for quantizers

Two tensor shapes make this model awkward, and both are shape properties that a name-based recipe will not notice:

• ffn_down_exps rows are 640 wide (moe_intermediate_size), and
• per_layer_token_embd rows are 160 wide.

Neither is divisible by 256, so K-quants and every 256-block I-quant (IQ4_XS, IQ3_XXS, IQ2_S, …) are illegal on them and silently fall back to 32-block types. That is 91.5 B of 176.9 B params — 51.7% of the file — with a floor near 4.5 bpw, which flattens the size/quality curve fast: pushing the remaining gate/up experts down to IQ2_XXS moves the total only from ~112 GB to ~77 GB. The expert gate/up tensors are unaffected (their rows are 2560 wide), which is why the recipe above can band them at IQ4_XS/IQ3_XXS.

per_layer_token_embd is a 51.2 B-param sparse lookup table — only a few rows are read per token — and at Q4_0 it is 28.8 GB, roughly a third of the file.

On a discrete-GPU system it is worth keeping in host RAM with -ot "per_layer_token_embd=CPU", since host memory is a separate and usually larger pool and the access pattern is cheap over PCIe.

On a unified-memory system (DGX Spark / GB10, Apple silicon) that does nothing: CPU and GPU share one pool, so there is nowhere to offload to. Budget the full file size as the footprint there, plus KV cache and compute buffers.

Provenance

• Source: Qwen/Qwen3.8-Flash-Next safetensors, 144 files, 360.0 GB, all verified byte-exact against the Hub after download.
• Converter: convert_hf_to_gguf.py from PR #27742, --outtype bf16, with one extra fix needed to convert this model at all (see the compatibility section).
• MIDDLE was quantized against an importance matrix carrying 926 entries over 4,000 calibration chunks.
• Unofficial community conversion — not affiliated with or endorsed by Qwen. Provided as-is, without warranty.