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BLACKFROST-3.8-ICED-BF16

BLACKFROST-3.8-ICED-BF16 is a Blackfrost Research modified BF16 checkpoint using the experimental Qwen4ExpForConditionalGeneration architecture. This is the full-precision speed-trial artifact; compression for smaller single-GPU targets is separate future work.

Checkpoint summary

  • BF16 safetensors checkpoint: 131 weight shards, approximately 360 GB on the Hub.
  • 48 text blocks with hybrid linear/full attention and a full-attention block every fourth layer.
  • Hidden size 2,560; 24 attention heads; 2 KV heads.
  • 512 routed experts, top-10 routing, plus a shared expert.
  • One native hybrid MTP layer is included in the checkpoint.
  • Configured maximum context: 262,144 tokens. The trial below used 32,768.
  • The repository contains a vision configuration, but the current validation and benchmark are text-only.

On 2026-09-15, all 131 local weight-shard SHA-256 hashes were checked against the corresponding Hub LFS object IDs with zero mismatches. The current Hub weights are therefore byte-identical to the modified BF16 speed-trial checkpoint.

Native MTP status

The embedded MTP tensors predate the latest trunk-weight modification, so the MTP head should be treated as provisional rather than freshly aligned to the modified model. It nevertheless provides a useful BF16 speculative-decoding baseline. A newly adapted MTP head should be evaluated separately before replacing these tensors.

Current runtime limitations for this hybrid architecture also matter:

  • Cross-request prefix-cache reuse is disabled by the tested vLLM build when native MTP is combined with the model's Mamba groups.
  • Fused multi-step draft decode is not yet available for the QWEN4_EXP_EXP_QSA_STATE attention backend, so metadata is rebuilt between speculative draft steps.

Four-B300 BF16 speed trial

Environment: four NVIDIA B300 SXM6 GPUs, tensor parallelism 4, vLLM 0.29.1rc1.dev13+g1cfd97281, 32,768-token serving context, sequential requests, and thinking enabled. The frozen suite contained eight reasoning, code, prose, and tool-result-synthesis prompts with temperature 1.0, top-p 0.95, top-k 20, seed 38421, and at most 256 generated tokens.

Mode Completion tokens Median decode Mean decode Median TTFT Draft acceptance Relative median
No draft 1,760 190.10 tok/s 190.51 tok/s 0.696 s n/a baseline
Native MTP, k=2 1,820 265.00 tok/s 264.27 tok/s 0.660 s 55.0% +39.4%
Native MTP, k=3 1,799 263.10 tok/s 288.43 tok/s 0.684 s 49.6% +38.4%

Per-position acceptance was 65.7% / 44.4% for k=2 and 66.8% / 47.8% / 34.3% for k=3. The k=3 mean was lifted by two unusually fast cases, while its median did not beat k=2. Native MTP with k=2 is therefore the current BF16 trial setting.

These are single-pass development measurements, not a production throughput claim. Workload, concurrency, context length, runtime build, and sampling settings can materially change the result.

Example vLLM launch

The benchmarked profile used exactly GPUs 0-3:

CUDA_VISIBLE_DEVICES=0,1,2,3 \
VLLM_WORKER_MULTIPROC_METHOD=spawn \
vllm serve Blackfrost-AI/BLACKFROST-3.8-ICED-BF16 \
  --served-model-name BLACKFROST-3.8-ICED-BF16 \
  --tensor-parallel-size 4 \
  --max-model-len 32768 \
  --max-num-seqs 4 \
  --gpu-memory-utilization 0.45 \
  --enable-prefix-caching \
  --trust-remote-code \
  --reasoning-parser qwen3 \
  --mamba-ssm-cache-dtype bfloat16 \
  --speculative-config.method mtp \
  --speculative-config.num-speculative-tokens 2

The model config specifies a float32 Mamba SSM cache. The command above deliberately overrides that cache to BF16 for this speed/memory trial; omit the override when evaluating the configured cache precision.

License

Use of this checkpoint is governed by the Qwen Community License 1.0. Review the license terms before use or redistribution.

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