Hy3 (295B) GGUF for ds4/NeutronStar (SSD streaming, CUDA)

Mixed-precision GGUF of tencent/Hy3 (295B total / 21B active MoE, Apache 2.0) built for the NeutronStar hy3 branch: a CUDA port of ds4 that streams routed experts from disk, so the model runs on GPUs that cannot hold it.

Reference machine: RTX 4060 Ti 16GB, Ryzen 9900X, 32GB RAM, one Gen4 NVMe. Per token only 8 of 192 experts per layer are read (~3GB/token at this quant); attention, shared experts, and the router stay resident. Measured on that box: ~1.8 t/s generation with a 16GB host expert cache (68% hit rate), interactive chat with KV retained across turns.

Provenance note (read this)

This build is a requantization of an existing quant, not of the original checkpoint. Source was the IQ4-UD edition of YanissAmz/Hy3-295B-A21B-GGUF (routed experts IQ4_XS/IQ3_S, attention and actives already Q8_0).

What that means in practice:

  • The tensors this recipe keeps at Q8_0 (attention, shared experts, dense FFN, embeddings, output head) were already Q8_0 in the source, so they pass through essentially lossless.
  • Only the routed experts went through a second quantization step (IQ4_XS/IQ3_S to IQ2_XXS). At a 2-bit target the 2-bit quantization noise dominates, so the expected quality loss vs a from-source build is small, but it is not zero.

A full-precision rebuild is coming: the same recipe run directly from the original BF16 checkpoint (tencent/Hy3, 598GB). It will replace this file in this repo when ready. If you are downloading for long-term use and can wait, wait for that one.

Recipe

The layout targets ds4's streaming expert cache: routed experts must be uniform fixed-size slabs, and everything that makes decisions stays high precision. Same design as antirez's GLM-5.2 ds4 build, including the MTP layer riding at Q2_K because importance matrices never cover the draft layer (imatrix generation runs normal forwards, which skip it).

Tensors Type Why
routed experts, layers 1-79 (gate/up/down) IQ2_XXS (imatrix) streamed from disk per token; uniform slabs
routed experts, layer 80 (MTP) Q2_K no imatrix coverage exists for the draft layer
attention q/k/v/output, all layers Q8_0 resident, paid once
shared expert + dense layer 0 FFN Q8_0 resident
nextn.eh_proj (MTP glue) Q8_0 tiny, no imatrix coverage
token embeddings, output head Q8_0 ds4 embed kernel contract
router (ffn_gate_inp), expert bias, all norms F32 decision makers stay exact

imatrix: the 125-chunk general-purpose matrix published with the source repo. Architecture string is hy-v3 (matching the source GGUFs; llama.cpp PR 25395 uses hy_v3, patched before quantizing).

Usage

git clone -b hy3 https://github.com/giannisanni/neutronstar
cd neutronstar && make ds4
./ds4 -m Hy3-ds4-IQ2XXS-AttnQ8.gguf --cuda --ssd-streaming \
  --ssd-streaming-cache-experts 64 --ctx 4096 --nothink

No prompt drops you into interactive chat (KV retained across turns). Useful knobs: DS4_CUDA_HOST_EXPERT_CACHE_GB=16 (host expert cache, the main speed lever; scale to your free RAM) and DS4_CUDA_PARALLEL_FETCH_THREADS=16.

MTP speculative decoding is not wired for Hy3 (and measurements on GLM/ DeepSeek show it cannot pay while expert streaming dominates eval cost); blk.80 is present in the file so it can be enabled later without requantizing.

Quantized with llama.cpp (PR 25395 + hy-v3 arch patch) on the reference machine.

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