QuantDiff

Best Qwen3.5 4B quant for a 16GB GPU

Short answer: Q8_0 from unsloth . Of the 8 Qwen3.5 4B files we tested that fit fully in 16GB with a 8192-token context, it has the smallest diff from the BF16 model (mean KLD 0.0019, same top token 98.3%).

Smallest diff that fits 16GB
Q8_0 by unsloth
File size
4.17 GB
KLD (mean)
0.0019
Same top token
98.3%
Tool calls
86.5%
Generation
114 t/s full GPU
Qwen3.5-4B-Q8_0.gguf
Runner-up
Q6_K by bartowski
File size
3.54 GB
KLD (mean)
0.0037
Same top token
97.1%
Tool calls
86.5%
Generation
130 t/s full GPU
Qwen_Qwen3.5-4B-Q6_K.gguf
Fastest that fits
UD-Q2_K_XL by unsloth
File size
1.81 GB
KLD (mean)
0.2425
Same top token
78.6%
Tool calls
76.0%
Generation
187 t/s full GPU
Qwen3.5-4B-UD-Q2_K_XL.gguf

Other budgets: 8GB12GB24GB ยท all 8 Qwen3.5 4B quants

How we picked

We estimate VRAM need as file size + f16 KV cache for 8192 tokens + about 0.6GB of compute buffers, and keep 0.5GB free for your desktop. Among files that fit, we rank by mean KL divergence against the BF16 model's logits, then by tool-call score. If you need a longer context, step down one quant level or quantize the KV cache (-ctk q8_0 -ctv q8_0). Methodology.

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