TL;DR

Family / related artifacts

Why this exists

DeepSeek-V4-Flash launched April 24, 2026 (284 B total / 13 B active, hybrid CSA + HCA attention, hash-routed experts). At release, no merged path through transformers + llm-compressor + vLLM existed for V4 quantization on Hopper or on SM 12.x Blackwell. RedHatAI/DeepSeek-V4-Flash-NVFP4-FP8 covered Blackwell datacenter (B100/B200, SM 10.x) via NVFP4 tcgen05 kernels, and Intel/DeepSeek-V4-Flash-W4A16-AutoRound covered W4A16 but explicitly excluded vLLM and SGLang. This artifact fills the gap: W4A16 GPTQ routed experts + FP8 block attention that serves on vLLM at TP=2 on H200 (Hopper SM 9.0a), DGX Spark (Blackwell SM 12.1a), and RTX PRO 6000 (Blackwell SM 12.0) — same weights, three SKUs.

Architecture & precision

Base model

Component precisions

Hardware validated

All three SKUs serve cuda graphs ON (no --enforce-eager). Same artifact, no weight changes between SKUs — only vLLM build flags and a few env vars differ.

Benchmarks

Quality

Sampling: greedy, temperature 0. lm-eval-harness via OpenAI-compatible backend pointing at the local vLLM. Methodology disclosed per row.

¹ The H200 GSM8K strict-match of 42.61% was a chat-format extraction artifact, not a quality regression. The flexible-extract number (92.87%) is the comparable figure. Cross-checked on DGX Spark / RTX PRO 6000 with corrected extraction (95.07–95.45%).

² ³ HumanEval pass@1 on H200 was initially reported as 54.27% under regex-based extraction. The harness was later corrected to use --confirm_run_unsafe_code (executes generated code), which raised the same-artifact score to 80.49%. The Spark and RTX PRO 6000 runs use the corrected methodology; the H200 number is the same artifact re-scored. See Changes for the dated correction.

⁴ Spark toolcall15 is scored across 3 thinking modes (45 cases); H200 / RTX PRO 6000 are single-round (30 cases). Scores normalized to %.

Comparison caveat: the H200 numbers come from an older vLLM build (harness HEAD 85aca32, jasl/vllm@428e08e). Spark and RTX PRO 6000 numbers are on today's ds4-sm120-experimental tip. The valid same-software comparison is DGX Spark ↔ RTX PRO 6000; H200 ↔ Blackwell deltas are informational.

Throughput

vllm bench serve random 1024-in / 1024-out, cuda graphs ON, MTP-spec n/a (this artifact ships without MTP).

Per-stream decode rate on RTX PRO 6000 is rock-stable across concurrency (TPOT mean stays at 21 ms, p99 only 23 ms). Aggregate input+output throughput at bs=2 reaches 420 tok/s.

Quick start

bash
Copy code
vllm serve canada-quant/DeepSeek-V4-Flash-W4A16-FP8 \
  --served-model-name DSV4-W4A16-FP8 \
  --tensor-parallel-size 2 \
  --kv-cache-dtype fp8 \
  --block-size 256 \
  --max-model-len 16384 \
  --max-num-seqs 4 \
  --gpu-memory-utilization 0.92 \
  --tokenizer-mode deepseek_v4 \
  --tool-call-parser deepseek_v4 \
  --enable-auto-tool-choice \
  --reasoning-parser deepseek_v4 \
  --trust-remote-code

Required env vars on SM 12.x sparse-MLA path: set VLLM_TRITON_MLA_SPARSE=1 and VLLM_TRITON_MLA_SPARSE_HEAD_BLOCK_SIZE=4. Without _HEAD_BLOCK_SIZE=4 the sparse-MLA Triton kernel crashes during warmup with RuntimeError: Triton Error [CUDA]: an illegal memory access was encountered in _dequantize_and_gather_k_kernel (kernel falls back to a default block size that doesn't match V4-Flash's head dim). Full env block at findings/QUICKSTART_DUAL_SPARK.md §4.

Long-context (1M tokens, single stream): drop --max-num-seqs to 1, --gpu-memory-utilization to 0.90, set --max-model-len 1048576 --max-num-batched-tokens 8192 --compilation-config '{"cudagraph_mode":"FULL_AND_PIECEWISE","custom_ops":["all"]}'.

Tensor parallelism: TP=2 is the only validated configuration. TP=1 OOMs on a single 141 GB H200; TP≥4 hits an upstream W4A16 MoE scale-sharding bug (vllm-project/vllm#41511).

RTX PRO 6000 (SM 12.0) only: set VLLM_USE_FLASHINFER_SAMPLER=0 — vLLM's FlashInfer-based top-p / top-k sampler JIT mis-parses the TORCH_CUDA_ARCH_LIST=12.0a token and incorrectly raises RuntimeError: FlashInfer requires GPUs with sm75 or higher.

Quantization recipe

Required calibration environment

bash
Copy code
export PYTORCH_CUDA_ALLOC_CONF=expandable_segments:True
export TORCH_NCCL_HEARTBEAT_TIMEOUT_SEC=3600
export TORCH_NCCL_BLOCKING_WAIT=0
export NCCL_TIMEOUT=3600
export TORCH_CUDA_ARCH_LIST=9.0a
sudo mount -o remount,size=1800G /dev/shm

expandable_segments is calibration-only — must not be set during vLLM serving.

What didn't work (recorded so others don't waste cycles)

Recipe

python
Copy code
from llmcompressor.modifiers.quantization import GPTQModifier
from compressed_tensors.quantization.quant_scheme import FP8_BLOCK, W4A16, QuantizationScheme

recipe = GPTQModifier(
    config_groups={
        "attention": QuantizationScheme(
            targets=[
                r"re:.*self_attn\.(q_a_proj|q_b_proj|kv_proj|o_a_proj|o_b_proj)$",
                r"re:.*self_attn\.compressor\.(gate_proj|kv_proj)$",
                r"re:.*self_attn\.compressor\.indexer\.(gate_proj|kv_proj|q_b_proj|weights_proj)$",
            ],
            **FP8_BLOCK,
        ),
        "experts": QuantizationScheme(
            targets=[r"re:.*mlp\.experts\.\d+\.(gate_proj|up_proj|down_proj)$"],
            **W4A16,
        ),
    },
    ignore=["lm_head"],
    offload_hessians=True,
    dampening_frac=0.1,
)

oneshot(
    model=model,
    dataset=ds,
    recipe=recipe,
    max_seq_length=512,
    num_calibration_samples=768,
    sequential_targets=["DeepseekV4DecoderLayer"],
    batch_size=4,
)

vLLM build

This artifact does not load on vanilla vLLM. Stack:

Single-file bootstrap script for dual DGX Spark: scripts/bootstrap_dsv4_spark.sh — does the whole stack zero-to-serving.

Upstream tracker: original PR #40991 (where Spark validation was posted) closed 2026-05-06; current tracker is PR #41834 — "[New Model][Nvidia] Add SM12x support for DeepSeek V4 Flash with essential fixes", branch codex/ds4-sm120-min-enable.

Honest limitations

• No MTP — transformers 5.8.1's _keys_to_ignore_on_load_unexpected = [r"(^|\.)mtp\..*"] silently strips MTP keys during calibration load. Speculative decoding cannot fire with this artifact. The W4A16-FP8-MTP successor retains MTP via a patched calibration path and delivers 1.49× spec-decode speedup at bs=1.
• TP > 2 blocked by vllm-project/vllm#41511 — W4A16 MoE scale-sharding bug.
• H200 numbers from older vLLM build — H200 baseline was scored on jasl/vllm@428e08e (harness HEAD 85aca32). Same-software comparison is DGX Spark ↔ RTX PRO 6000; H200 → Blackwell deltas are informational.
• toolcall15 TC-06 (Multi-Value Extraction) and TC-08 (Conditional Branching) also fail on the native FP4/FP8 baseline — V4-Flash model-architecture limits, not quantization defects.
• 2026-05-25: artifact has shipping issues on current upstream vLLM. Two problems were surfaced when attempting to load this artifact on jasl/vllm@a02a3778f (the post-PR-#40923 build the sibling W4A16-MTP card now uses): (1) Same FP8_BLOCK compressor/indexer shipping bug as the MTP sibling — current vLLM constructs those modules as plain BF16 (quant_config=None) and the artifact fails with KeyError: 'layers.10.attn.mla_attn.compressor.fused_wkv_wgate.weight_scale'. The MTP sibling fixed this by dequantizing those weights in-artifact to BF16; this artifact has not yet had that fix applied. (2) A separate architecture-drift issue: the artifact lacks the layers.N.ffn.gate.e_score_correction_bias tensor that current upstream vLLM's DSV4 loader requires (KeyError). Either re-calibration that emits this tensor, or a defensive .get() loader patch upstream is needed. The published H200/Spark/RTX PRO 6000 numbers above remain valid for their original jasl/vllm@ds4-sm120-experimental@abad5dc71 build (2026-05-05); they do not currently reproduce on bleeding-edge vLLM. Tracking and re-verification deferred to the next session.

Reproduction

Full toolchain, scripts, patches, mission report: canada-quant/dsv4-flash-w4a16-fp8.

Single-file bootstrap (dual DGX Spark, idempotent, SSH-orchestrated):

bash
Copy code
curl -fsSLO https://raw.githubusercontent.com/canada-quant/dsv4-flash-w4a16-fp8/main/scripts/bootstrap_dsv4_spark.sh
chmod +x bootstrap_dsv4_spark.sh
./bootstrap_dsv4_spark.sh --head-host spark-a --worker-host spark-b

Upstream contributions filed during this work

Changes

Files in the artifact

• ~30 sharded model-*.safetensors files + model.safetensors.index.json (~143 GB total)
• config.json — vLLM-compatible quantization_config (W4A16 + FP8_BLOCK groups)
• tokenizer.json, tokenizer_config.json, generation_config.json — upstream DSV4-Flash
• recipe.yaml — the llm-compressor calibration recipe
• chat_template.jinja — upstream DSV4-Flash (unchanged)
• README.md — this file

Citation

bibtex
Copy code
@misc{canada-quant-dsv4-flash-w4a16-fp8-2026,
  title  = {DeepSeek-V4-Flash W4A16-FP8 for vLLM on Hopper and Blackwell},
  author = {Canada Quant},
  year   = {2026},
  publisher = {Hugging Face},
  url    = {https://huggingface.co/canada-quant/DeepSeek-V4-Flash-W4A16-FP8}
}

License

MIT, inherited from upstream deepseek-ai/DeepSeek-V4-Flash.

Acknowledgments

• @jasl — DeepSeek-V4 vLLM SM12x base support (PR #40991 → #41834); memory-pressure-release fix e734ace5 that resolved the Blackwell 256K×2 stall.
• @kylesayrs — compressed-tensors V4 attention path (PR #41276).
• @aabbccddwasd — indexer KV cache layout fix.
• @bbbearxyz — SM12x Triton fallback kernels.
• @wuwenthink — SM12x harness validation.
• RedHatAI/DeepSeek-V4-Flash-NVFP4-FP8 — published reference for V4 mixed-precision attention topology.