BigBang-v1 W4A16 NVFP4 + MTP

NVIDIA ModelOpt quantization of endless-frontier/BigBang-v1, based on Qwen3.6-35B-A3B. This checkpoint includes the native MTP module and has been tested with vLLM on one NVIDIA DGX Spark-class system.

This is a quantization of the upstream model, not an additional fine-tune.

Quantization

Component Format
MoE and shared-expert MLP weights W4A16 NVFP4, group size 16
Attention projections FP8
Language-model output head W4A16 NVFP4
Vision and other excluded modules BF16
Native MTP module BF16

The checkpoint was produced with NVIDIA ModelOpt 0.45.0 and is approximately 21.8 GiB across four safetensor shards. Exact layer assignments are recorded in hf_quant_config.json.

vLLM

Tested with vLLM 0.25.1, FlashInfer attention, the Marlin MoE backend, a BF16 KV cache, and Qwen reasoning/tool parsers.

vllm serve TheShed/BigBang-v1-W4A16-NVFP4-MTP \
  --trust-remote-code \
  --kv-cache-dtype bfloat16 \
  --attention-backend flashinfer \
  --moe-backend marlin \
  --speculative-config '{"method":"mtp","num_speculative_tokens":1,"moe_backend":"triton"}' \
  --reasoning-parser qwen3 \
  --enable-auto-tool-choice \
  --tool-call-parser qwen3_xml

MTP is optional. To serve the target model without speculative decoding, omit the --speculative-config argument. A separate non-MTP checkpoint is not required.

Notes

  • The architecture supports up to 262,144 tokens. Usable context and concurrency depend on available memory and KV-cache configuration.
  • Although the quantization metadata advertises FP8 KV cache, BF16 KV was used for testing because calibrated FP8 KV scales are not included.
  • No formal quality, throughput, or multimodal comparisons against the upstream BF16 checkpoint are provided.
  • The upstream model's limitations and safety considerations still apply.

Attribution and license

Released under the Apache License 2.0, matching the upstream model.

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