MiniMax-M2.7-PrismaQuant-3.20bit-vllm

MiniMax-M2.7 — PrismaQuant 3.20 bpp (vLLM)

Mixed-precision quantization with joint expert pruning. Fits a 228 B parameter MoE in 90 GB on a single DGX Spark, served natively by vLLM with no patches.

Source: MiniMaxAI/MiniMax-M2.7 Quantizer: prismaquant · commit pinned in this artifact's mixed_native_manifest.json

TL;DR

How it was produced

prismaquant solves a multi-choice knapsack over per-Linear cost / memory choices to land at a target bit budget. Two distinct contributions go into this artifact:

1. Closed-form Δloss proxy

For each (Linear, format) pair, the cost is

$$\Delta\mathrm{loss} \approx \tfrac{1}{2} \cdot H_{\text{trace}} \cdot \mathrm{MSE}_W$$

• H_trace is the empirical Fisher diagonal trace, captured in one streaming forward+backward pass over the calibration set. It measures how curved the cross-entropy loss is at this Linear: high H_trace means a small weight perturbation moves the loss a lot.
• MSE_W is the measured per-format weight round-trip error (NVFP4, FP8, BF16). Not an analytical formula — we run RTN on the actual weights and compute the error directly.

Multiplying gives the second-order Taylor estimate of how much the model's loss will rise if you replace the BF16 weight with the format's quantized version. The allocator picks per-Linear formats that minimize total Δloss subject to a total-bit budget.

2. Joint expert-prune + format choice

For MoE layers, prismaquant treats each MoE choice as a pair:

(quantization_format, dropped_expert_ids)

Both the format and the prune set are priced in the same knapsack via REAP-style saliency:

$$S_j = \frac{1}{T_{\text{cal}}} \sum_t g_j(t) \cdot \lVert f_j(t) \rVert_2^2$$

This is the dropout-loss estimate from the REAP family of MoE expert-importance scores: how much the layer's output norm drops in expectation when expert j is removed, weighted by the gradient signal flowing through that expert. Sum across experts and you get a per-(router, expert) score in Δloss units, directly comparable to the quantization Δloss.

Per-layer prune candidates emit floor(R · num_experts) lowest-S experts at each ratio R; the DP picks (R, format) jointly. After the pareto sweep, prismaquant produces a uniform-kept prune manifest so vLLM's MoE kernel sees a single num_local_experts per layer (this artifact: 176 of 256 kept everywhere).

3. Pareto sweep + kneedle pick

Before committing to a target bit budget, prismaquant computes the full pareto curve. Below is the actual sweep that produced this artifact:

The Δloss plateau between 3.16 and 3.40 (~3,732) shows the allocator is already squeezing most of the available signal in that band. The dramatic drop at 3.50 (-33 %) is from relaxing the prune ratio (15,872 → 11,904 experts dropped). The user-specified target was the 90-95 GB band; 3.20 was picked as the smallest practical size that captures essentially all the available quality in the band.

Format mix on disk

NVFP4       : 30,780 Linears (94.5 %)  — experts + most attention/MLP projections
FP8_SOURCE  :  2,204 Linears  (6.7 %)  — passthrough of natively-FP8 source weights
BF16        :     62 routers          — output dim shrunk to kept-expert count
PRUNED      : 14,880 Linear slots     — 4,960 experts × 3 weights, dropped per REAP

Sample of per-layer assignments:

The allocator put the early dense layers (which dominate semantic embedding pathways) at FP8 for safety, then dropped the bulk of MoE expert weights to NVFP4 once their 0.5 · H · MSE_W showed it was safe. A few attention projections in mid-layers got FP8_SOURCE-pinned where the per-Linear sensitivity flagged NVFP4 as too aggressive.

Calibration

Calibration data: cal-mix-v1, a multi-domain mix balancing agentic, math, and coding sequences:

• Agentic: tool-call traces, multi-step reasoning chains, planning + execution dialogues
• Math: word problems, step-by-step solutions, symbolic manipulation
• Coding: Python / Rust / SQL / shell, both authoring and reading patterns

Volume: 32 chunks × 4 samples × 2048 seq-len ≈ 262 k tokens through the streaming probe. Each chunk runs phase-1 forward (saliency capture) + phase-3 reverse-sweep (Fisher per-Linear). The chunks share the same multi-domain composition — so all calibration matters for all three downstream regimes.

prismaquant's per-domain-saliency feature exists (allocator can use union / intersection / mean across domains), but for this release the calibration was domain-merged. Per-domain runs are a follow-up.

Quality

Spot-checked at temperature 0 across agentic / math / coding:

Formal benchmarks (MMLU, GSM8K, HumanEval) deferred. The artifact is positioned as fits-on-Spark + serves-coherently across the three calibration domains; rigorous benchmark numbers in a follow-up release.

Serving

vllm serve <this-repo> \
  --quantization compressed-tensors \
  --trust-remote-code \
  --max-model-len 32768 \
  --max-num-seqs 4 \
  --gpu-memory-utilization 0.85 \
  --kv-cache-dtype fp8 \
  --enable-prefix-caching \
  --enable-auto-tool-choice \
  --tool-call-parser minimax_m2 \
  --reasoning-parser minimax_m2

Recommended on UMA hardware: PYTORCH_CUDA_ALLOC_CONF=expandable_segments:True to keep the cuda allocator from hoarding freed blocks.

Limitations / caveats

• Calibration scale: 262 k tokens is moderate. Heavy reasoning-chain or long-context workloads may benefit from a re-export with more diverse calibration.
• Domain-merged saliency: per-domain prune policies (union/intersection) supported by prismaquant but not exercised here. A re-export with domain-tagged calibration is a candidate next iteration.
• No formal benchmarks yet: MMLU / GSM8K / HumanEval pending. Headline result is "fits + coherent across cal-mix".
• No MTP heads: MiniMax-M2 has no MTP head (unlike Qwen3.5/3.6). No speculative-decoding accelerator.
• Pruned experts are gone: 4,960 of 15,872 (31 %) dropped per REAP. Tasks heavily dependent on those specific experts could see degradation. Empirical probes show none on agentic/math/coding prompts.

Reproduction

This artifact was produced by:

# 1. Probe + cost (multi-chunk, adaptive sampling, deferred Fisher sync)
python -m prismaquant.multi_chunk_probe \
  --chunks-dir /work/chunks \
  --model <minimax-m2.7-snapshot> \
  --output /work/artifacts/probe.pkl \
  --activation-cache-dir /work/act \
  --work-dir /work/work \
  --layers-per-shard 4 --unified-sweep \
  --no-include-mtp --no-include-visual --no-include-lm-head \
  --prefetch-lookahead 4 --prefetch-workers 2 \
  --activation-rows-limit 256 \
  --calibration-modality text-only \
  --retain-cross-chunk-cache \
  --adaptive-sampling \
  --run-cost --cost-output /work/artifacts/cost.pkl \
  --cost-formats NVFP4,MXFP8_E4M3,FP8_SOURCE,BF16

# 2. Allocator (target_bits=3.20 picks the kneedle within the 90-95 GB band)
python -m prismaquant.allocator \
  --probe /work/artifacts/probe.pkl \
  --costs /work/artifacts/cost.pkl \
  --formats NVFP4,MXFP8_E4M3,FP8_SOURCE,BF16 \
  --target-bits 3.20 \
  --pareto-targets 3.10,3.16,3.20,3.25,3.30,3.40,3.50,3.60 \
  --enable-expert-prune \
  --prune-ratios 0.0,0.125,0.1875,0.25,0.3125,0.375 \
  --prune-alpha 0.15 \
  --layer-config /work/artifacts/layer_config_prune.json

# 3. Export (native compressed-tensors, GPTQ + scale-sweep activation-aware)
python -m prismaquant.export_native_compressed \
  --model <minimax-m2.7-snapshot> \
  --layer-config /work/artifacts/layer_config_prune.json \
  --prune-manifest /work/artifacts/layer_config_prune.json.prune.json \
  --output /work/exported \
  --activation-cache-dir /work/act \
  --device cuda

Full source + reproduction notes: https://github.com/RobTand/prismaquant

Acknowledgements

• MiniMaxAI — source model.
• vLLM — compressed-tensors serving stack with native NVFP4 + FP8 MoE kernels.
• REAP-style per-expert dropout-loss saliency.
• HAQ / HAWQ-V1/V2/V3 (Wang, Dong, Yao, et al.) — mixed-precision allocation foundations.
• GPTQ (Frantar et al. 2022), AutoRound — per-Linear quantizer building blocks.

License

Inherits the MiniMax-M2.7 license from the source model. See base model card for terms.