Qwen3-4B-Instruct-2507 โ€” BitClass Mixed-Precision GGUF

Mixed-precision GGUF quantizations of Qwen3-4B-Instruct-2507 using learned per-tensor quantization profiles. Each tensor group receives the precision level that minimizes quality loss for its importance โ€” more bits where they matter, fewer where they don't.

Seven precision levels from ultra-compact (3.0 bpw) to high quality (4.5 bpw). Low-BPW models use IQ types for better quality-per-bit; higher levels use KQ types for faster inference.

Models

File Target BPW Size PPL โ†“ Family
Qwen3-4B-Instruct-2507-MX-3.0bpw.gguf 3.0 1.72 GB 3.073 IQ
Qwen3-4B-Instruct-2507-MX-3.2bpw.gguf 3.2 1.79 GB 3.034 IQ
Qwen3-4B-Instruct-2507-MX-3.4bpw.gguf 3.4 1.88 GB 2.971 IQ
Qwen3-4B-Instruct-2507-MX-3.6bpw.gguf 3.6 2.02 GB 2.936 KQ
Qwen3-4B-Instruct-2507-MX-3.8bpw.gguf 3.8 2.03 GB 2.951 KQ
Qwen3-4B-Instruct-2507-MX-4.0bpw.gguf 4.0 2.01 GB 2.928 KQ
Qwen3-4B-Instruct-2507-MX-4.5bpw.gguf 4.5 2.47 GB 2.932 KQ

Target BPW is the planner's per-tensor bit budget (and the filename label). The actual whole-file BPW runs ~0.3โ€“0.4 higher, because output/embedding tensors are kept at higher precision and GGUF carries metadata overhead โ€” see the Size column for the real footprint.

Recommended: MX-3.4bpw for the best quality-to-size ratio. MX-3.0bpw for maximum compression. MX-4.0bpw for the highest quality in this ladder.

How It Compares

Model BPW Size PPL โ†“ Source
ByteShape KQ 3.34 3.34 1.69 GB 3.121 byteshape
โ˜… Ours MX-3.0 3.0 1.72 GB 3.073 This repo
โ˜… Ours MX-3.2 3.2 1.79 GB 3.034 This repo
Unsloth Q3_K_S 3.75 1.75 GB 3.007 unsloth
โ˜… Ours MX-3.4 3.4 1.88 GB 2.971 This repo
โ˜… Ours MX-3.6 3.6 2.02 GB 2.936 This repo
โ˜… Ours MX-4.0 4.0 2.01 GB 2.928 This repo
Unsloth Q4_K_M 4.97 2.32 GB 2.956 unsloth
โ˜… Ours MX-4.5 4.5 2.47 GB 2.932 This repo

All models benchmarked in the same session on identical hardware (NVIDIA GB10 ATOM, GPU) for fair comparison.

Key Results

  • Lower perplexity than ByteShape KQ 3.34: MX-3.0 (PPL 3.073) vs 3.121 โ€” 1.5% better, at comparable size (1.72 vs 1.69 GB)
  • Lower perplexity than Unsloth Q3_K_S: MX-3.4 (PPL 2.971) vs 3.007 โ€” 1.2% better, at 1.88 vs 1.75 GB
  • Lower perplexity than Unsloth Q4_K_M: MX-4.5 (PPL 2.932) vs 2.956 โ€” 0.8% better, at 2.47 vs 2.32 GB

Running with Ollama

# Pick any precision level
ollama run hf.co/sh111111111111111/Qwen3-4B-Instruct-2507-BitClass-GGUF:Qwen3-4B-Instruct-2507-MX-3.4bpw.gguf

Running with llama.cpp

# Chat
llama-cli -m Qwen3-4B-Instruct-2507-MX-3.4bpw.gguf -cnv

# Server (OpenAI-compatible API)
llama-server -m Qwen3-4B-Instruct-2507-MX-3.4bpw.gguf --port 8080

# Benchmark
llama-perplexity -m Qwen3-4B-Instruct-2507-MX-3.4bpw.gguf -f your_eval_data.txt

Benchmarking Details

All benchmarks run with llama.cpp (commit 406f4e3) on NVIDIA GB10 ATOM GPU with full offload (-ngl 999). Perplexity measured via llama-perplexity on a held-out evaluation set (20 chunks, 512 context). Throughput via llama-bench (512 prompt / 128 generation tokens). All models โ€” ours, Unsloth, ByteShape โ€” benchmarked in the same session.

Disclaimer

Independent project. Not affiliated with or endorsed by Qwen, Unsloth, ByteShape, Bartowski, or llama.cpp. Competitor figures are from our own benchmark harness and may differ from those projects' self-reported numbers; competitor file sizes reflect the revision we tested and may since have changed.

License

Apache 2.0, inherited from Qwen3-4B-Instruct-2507.

Acknowledgments

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