Hy3-preview-NVFP4

Hy3-preview NVFP4 (weight-only)

NVFP4 quantization of tencent/Hy3-preview — Tencent's 295B Mixture-of-Experts model (21B active, 192 routed + 1 shared expert, 8 experts/token, 256K context, unified fast/deep-reasoning) — for serving on vLLM.

This is a weight-only NVFP4 (NVFP4-A16) checkpoint. The routed-expert FFN tensors — which are ~98% of the model — are quantized to NVFP4 (NVIDIA's 4-bit float, E2M1 with FP8-E4M3 per-16-block scales and an FP32 per-tensor global scale). Every outlier-sensitive path is deliberately kept in BF16: all self-attention (Q/K/V/O), the shared expert, the MoE routers/gates, the dense-MLP layer, the MTP head, token embeddings, lm_head, and all norms. Activations stay BF16 (no activation quantization). Because the experts dominate the memory footprint, quantizing only them recovers almost all of the size reduction while protecting quality where it matters most.

Produced with NVIDIA ModelOpt 0.45.0 via a memory-frugal shard-streaming pass (no calibration data — weight-only NVFP4 derives its scales from the weights themselves), so the packing is exactly what vLLM's NVFP4 loader expects.

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Why NVFP4? On NVIDIA Blackwell GPUs (RTX 50-series, B100/B200, GB10/DGX Spark) NVFP4 weights run on native FP4 tensor-core kernels, and the 4-bit expert weights cut both VRAM and the memory bandwidth that dominates MoE decode. This gives format parity with the NVFP4 path used by vLLM / SGLang / TensorRT-LLM.

What's quantized

Files

112 sharded safetensors (~169 GB total) + config.json carrying the quantization_config (ModelOpt NVFP4, weight-only). Load directly in vLLM.

Usage (vLLM)

On datacenter Blackwell (B200, sm_100) or RTX 50-series (sm_120) the default NVFP4 MoE kernels work out of the box:

vllm serve LibertAIDAI/Hy3-preview-NVFP4 \
  --tensor-parallel-size 2 \
  --trust-remote-code

On GB10 / DGX Spark (sm_121) the native FP4 MoE kernels currently have gaps, so force the marlin MoE backend (dequant-to-FP16 path, works on sm_121):

# 2× GB10, CUDA-13 image
vllm serve LibertAIDAI/Hy3-preview-NVFP4 \
  --tensor-parallel-size 2 \
  --moe-backend marlin \
  --enforce-eager \
  --trust-remote-code

Requires a vLLM build with HYV3ForCausalLM support (vLLM ≥ 0.23) and a CUDA-13 image on GB10. A full 2× GB10 deployment recipe (multinode fabric, memory tuning, the exact kernel gotchas) is published separately. Verified serving on a 2× NVIDIA GB10 (Grace Blackwell, sm_121) cluster at tensor-parallel = 2 (coherent generation, correct arithmetic).

Provenance & method

• Base: tencent/Hy3-preview (BF16, 112 shards, 598 GB).
• Quantizer: shard-streaming ModelOpt NVFP4QTensor weight-only pass; expert FFN → NVFP4, everything else copied through in BF16.
• Verification: per-expert round-trip cosine ≈ 0.995 vs the BF16 source.

Quantized by LibertAI. Not affiliated with Tencent. Subject to the Tencent Hy Community License.