What was changed
- Quantized with
bitsandbytes NF4 double-quant (bnb_4bit_quant_type=nf4, bnb_4bit_compute_dtype=bfloat16)
- Visual tower layers kept at bf16 (
llm_int8_skip_modules) — required for correct image inference
lm_head.weight kept at bf16 for output quality
Model family

The visual tower is a bf16 overhead that scales with model size (~0.19 GB for 0.8B, ~0.62 GB for 2B/4B, ~0.85 GB for 9B).
BNB-quantized models are roughly 40% of the original f16 size (exact ratio varies by size).
Fine-tuning
Text-only LoRA fine-tuning — use the text-only BNB variant as training base:
techwithsergiu/Qwen3.5-text-4B-bnb-4bit
Training pipeline (QLoRA · Unsloth · TRL):
github.com/techwithsergiu/qwen-qlora-train
VLM (image + text) fine-tuning — refer to the official Unsloth guide:
unsloth.ai/docs/models/qwen3.5/fine-tune
Pipeline diagram

Conversion
Converted using qwen35-toolkit —
a Python toolkit for BNB quantization, visual tower removal, verification and
HF Hub publishing of Qwen3.5 models.
Acknowledgements
Based on Qwen/Qwen3.5-4B
by the Qwen Team. If you use this model in research, please cite the original:
@misc{qwen3.5,
title = {{Qwen3.5}: Towards Native Multimodal Agents},
author = {{Qwen Team}},
month = {February},
year = {2026},
url = {https://qwen.ai/blog?id=qwen3.5}
}