QLoRA Distillation: 4B Student Matches 72B Teacher on Classification (72%→91%) and JSON Extraction

Dangerous-Nerve-7766 · reddit · 2026-08-21

Experiment comparing a fine-tuned 4B model against a 72B teacher on narrow, repetitive tasks: support ticket classification and invoice JSON extraction. Synthetic data was generated by Qwen2.5-72B-Instruct. QLoRA was applied to Qwen3-4B-Instruct-2507.

Results:

Key Insight: The zero-shot baseline failed miserably on invoice extraction (1.2% fully correct) because it systematically violated schema null conventions (e.g., inventing subtotals). Fine-tuning significantly improved accuracy and, crucially, adherence to strict schema rules. Cost was under $2 per run on a rented 4090.

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