Quantization Details
Table with columns: Parameter, Value| Parameter | Value |
|---|
| Method | AQLM + OA-EM init + PV-tuning |
| Bitrate | 2 bpp (2 codebooks × 8-bit, group size 8) |
| Codebook config | num_codebooks=2, nbits_per_codebook=8, in_group_size=8 |
| Beam size | 8 |
| OA-EM config | 3 rounds, 100 Adam steps, lr=1e-4 |
| PV-tuning | 5 epochs, LAMB optimizer, lr=3e-4, 10K C4 samples |
| Seed | 42 |
| Context length | 4096 tokens |
Results
Perplexity
Table with columns: Model, Pre-PV Wiki-2, Pre-PV C4, Post-PV Wiki-2, Post-PV C4| Model | Pre-PV Wiki-2 | Pre-PV C4 | Post-PV Wiki-2 | Post-PV C4 |
|---|
| AQLM Greedy | 12.50 | 16.01 | 10.93 | 14.57 |
| AQLM OA-EM | 12.30 | 16.08 | 10.73 | 14.49 |
Downstream Tasks (post-PV-tuning, b=8)
Table with columns: Task, Metric, AQLM Greedy, AQLM OA-EM| Task | Metric | AQLM Greedy | AQLM OA-EM |
|---|
| ARC-Challenge | acc_norm ↑ | .375 | .366 |
| ARC-Easy | acc_norm ↑ | .662 | .651 |
| HellaSwag | acc_norm ↑ | .626 | .630 |
| LAMBADA | acc ↑ | .600 | .587 |
Note: On Qwen, the baseline holds a small downstream advantage (0.606 vs 0.603 average accuracy), consistent with the mild initialisation bottleneck on this architecture. OA-EM wins on perplexity (both WikiText-2 and C4 after PV-tuning).
Usage
from transformers import AutoModelForCausalLM, AutoTokenizer model = AutoModelForCausalLM.from_pretrained( "kennedyian94/Qwen-2.5-3B-AQLM-OA-EM-2Bit-2x8", trust_remote_code=True, torch_dtype="auto", device_map="auto")tokenizer = AutoTokenizer.from_pretrained("kennedyian94/Qwen-2.5-3B-AQLM-OA-EM-2Bit-2x8") inputs = tokenizer("The meaning of life is", return_tensors="pt").to(model.device)outputs = model.generate(**inputs, max_new_tokens=100)print(tokenizer.decode(outputs[0], skip_special_tokens=True))
Note: Requires the aqlm inference library:
Paper
Initialisation Determines the Basin: Efficient Codebook Optimisation for Extreme LLM Quantization
Ian W. Kennedy and Nafise Sadat Moosavi, University of Sheffield
arXiv:2604.08118 | Code
Citation
@article{kennedy2026oaem, title={Initialisation Determines the Basin: Efficient Codebook Optimisation for Extreme LLM Quantization}, author={Kennedy, Ian W. and Moosavi, Nafise Sadat}, journal={arXiv preprint arXiv:2604.08118}, year={2026}}