GLM-5.3-Flash-NVFP4

GLM-5.3-Flash — NVFP4 (experts-only, 4/6-optimal scales)

TL;DR — the plain-English version

What this is: GLM-5.3-Flash, one of the strongest open models released this year, shrunk from 660 GB down to ~196 GB so it can run on a single multi-GPU machine instead of a server rack — with quality kept as close to the original as the format allows.

How: the model's "experts" (where ~90 % of its bulk lives) are stored in NVFP4 — a 4-bit number format that NVIDIA's newest (Blackwell) GPUs understand natively. Everything quality-critical — attention, the vision system, the speculative-decoding head — is left completely untouched at full precision.

Is the quality still good? The compressed weights land within ~8 % relative error of the originals per-tensor (measured, not guessed — numbers below), which is at the good end of what 4-bit formats achieve. We also used a scale-picking trick that cuts error ~19 % compared to how most 4-bit quants are made.

Can I run it today?

• ✅ H100 / B200-class GPUs (≥ ~4× 80 GB): yes — command below.
• ⏳ RTX PRO 6000 / consumer Blackwell (SM120): not yet — a missing GPU kernel in vLLM, being fixed in the open right now (vllm#53963 — filed by us, with this exact checkpoint as the test artifact). Watch that issue; when it closes, this runs.

New to quantization? Think of it as saving a photo as a high-quality JPEG instead of RAW: dramatically smaller, nearly indistinguishable, and this card documents exactly how much was lost and where — so you don't have to take our word for it.

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Weight-only NVFP4 (NVFP4A16) quantization of zai-org/GLM-5.3-Flash — Z.ai's ~320B/A18B natively-multimodal MoE (hybrid linear attention + rope-free sparse MLA) — in standard compressed-tensors nvfp4-pack-quantized format. ~196 GB.

Quantized from the true BF16 release (zai-org/GLM-5.3-Flash-BF16, pinned b1967181), not the FP8 export — no double-quantization on the experts.

What makes this build different

Most NVFP4 quants use plain round-to-nearest with amax/6 block scales. This build selects block scales per 16-element block by exact post-rounding squared error, choosing between the classic amax/6 plan and NVIDIA ModelOpt's four-over-six plan (M ∈ {4, 6}, 256-normalized global scale) per tensor — never worse than classic RTN by construction.

Measured on this model (48-tensor random sample, against the BF16 source as ground truth):

For reference, the other public NVFP4 of this model reports rel-err ≈ 0.0925 with plain RTN (same experts-only recipe; their card, their measurement).

What is quantized, what is not

• NVFP4: routed-expert weights only — 36,288 tensors (42 MoE layers × 288 experts × 3 projections), ≈ 90 % of parameters.
• BF16 (untouched): all attention (MLA incl. kv_b_proj, linear-attention layers, DSA indexer), shared experts, dense MLPs, router gates, embeddings, lm_head, the full vision tower (byte-identical to source — verified tensor-by-tensor), and the MTP layer (kept full-precision so vendor-style speculative decoding works: --speculative-config '{"method":"mtp","num_speculative_tokens":5}').

Verification (receipts, not vibes)

• Quantization math bit-exact vs an llmcompressor NVFP4A16 oneshot and byte-identical vs NVIDIA ModelOpt's NVFP4QTensor export path (packed weights, E4M3 block scales, global scales) at the pinned toolchain: torch 2.13.0 / compressed-tensors 0.18.0 / safetensors 0.8.0.
• Exact expert census asserted at build time; all values verified on the FP4 grid.
• Vision tower byte-compared against the source (347 tensors).
• MANIFEST.sha256 covers every file.
• Not measured: end-to-end perplexity/evals (see serving status below). Weight-fidelity metrics only — stated plainly.

Serving status (read this)

glm5_next is not yet in vLLM main (support PR: vllm#53906). vLLM publishes dedicated per-model images; this checkpoint loads cleanly there (Marlin NVFP4 auto-selected):

docker run --gpus all --ipc=host -p 8000:8000 \
  vllm/vllm-openai:glm53-flash-x86_64-cu130 \
  --model dabsLabs/GLM-5.3-Flash-NVFP4 \
  --tensor-parallel-size 4 \
  --reasoning-parser glm45 --tool-call-parser glm47 --enable-auto-tool-choice \
  --max-num-seqs 256

• H100 / B200 / GB200: expected to serve (vendor-verified hardware for the image).
• SM120 (RTX PRO 6000 / consumer Blackwell): currently blocked upstream — the image's sparse-MLA kernels don't cover rope-free MLA on SM120. Full three-failure-mode dossier and fix tracking: vllm#53963 (filed by us; this exact checkpoint is the test artifact). --kv-cache-dtype and backend workarounds do not help — it's a kernel gap, not a config issue.
• Set VLLM_ENGINE_READY_TIMEOUT_S=3600: engine init on a 320B MoE is slow.

Provenance

Source revision pinned; conversion is a streaming shard-by-shard pass (the model is never materialized), quantization primitives called directly from compressed-tensors. Built and verified on 2026-08-26. MIT, as is the base model.

Quantized by dabsLabs.