How to use from
Pi
Start the MLX server
# Install MLX LM:
uv tool install mlx-lm
# Start a local OpenAI-compatible server:
mlx_lm.server --model "plawanrath/qwen2.5-7b-instruct-q6-mlx-cba"
Configure the model in Pi
# Install Pi:
npm install -g @mariozechner/pi-coding-agent
# Add to ~/.pi/agent/models.json:
{
  "providers": {
    "mlx-lm": {
      "baseUrl": "http://localhost:8080/v1",
      "api": "openai-completions",
      "apiKey": "none",
      "models": [
        {
          "id": "plawanrath/qwen2.5-7b-instruct-q6-mlx-cba"
        }
      ]
    }
  }
}
Run Pi
# Start Pi in your project directory:
pi
Quick Links

qwen2.5-7b-instruct-q6 (MLX, CBA artifact)

MLX-format 6-bit (Q6) variant of Qwen/Qwen2.5-7B-Instruct.

This is one of the 15 model artifacts from the paper:

Quantization Undoes Alignment: Bias Emergence in Compressed LLMs Across Models and Precision Levels Plawan Kumar Rath, Rahul Maliakkal. IEEE Cloud Summit 2026. Code: https://github.com/plawanrath/compression-bias-amplification arXiv: https://arxiv.org/abs/2605.15208

Quantization

Weight-only post-training quantization via mlx_lm.convert:

  • bits: 6
  • group_size: 64
  • mode: affine

How this artifact was produced

python -m mlx_lm.convert \
    --hf-path Qwen/Qwen2.5-7B-Instruct \
    --mlx-path ./qwen2.5-7b-instruct-q6 \
    --quantize \
    --q-bits 6 \
    --q-group-size 64

This is the exact artifact used to produce the inference results in §4.3 of the paper (911,100 records over BBQ ambiguous, 5 seeds × 12,148 items × 15 configs).

Usage (MLX)

pip install mlx-lm
from mlx_lm import load, generate

model, tokenizer = load("plawanrath/qwen2.5-7b-instruct-q6-mlx-cba")
prompt = tokenizer.apply_chat_template(
    [{"role": "user", "content": "Hello!"}],
    add_generation_prompt=True,
    tokenize=False,
)
print(generate(model, tokenizer, prompt=prompt, max_tokens=128))

Or via CLI:

mlx_lm.generate --model plawanrath/qwen2.5-7b-instruct-q6-mlx-cba --prompt "Hello!"

Paper findings relevant to this variant

The paper documents a dose-response relationship between quantization aggressiveness and emergent stereotypical behavior on BBQ ambiguous questions:

Variant % of BF16-unbiased items that became biased
Q8 0.1–0.9%
Q6 0.3–1.3%
Q4 2.2–5.6%
Q3 6.0–21.1%

These changes are largely invisible to perplexity (<0.5% shift at Q8, <3% at Q4 across all three families). Treat any deployment of compressed instruction-tuned models on fairness-sensitive tasks accordingly.

Model details

License

Inherited from the base model (apache-2.0). See the upstream model page for the full license text.

Citation

@inproceedings{rath2026quantization,
  title     = { Quantization Undoes Alignment: Bias Emergence in Compressed LLMs Across Models and Precision Levels },
  author    = {Rath, Plawan Kumar and Maliakkal, Rahul},
  booktitle = { IEEE Cloud Summit 2026 },
  year      = {2026},
  eprint    = {2605.15208},
  archivePrefix = {arXiv},
  url       = {https://arxiv.org/abs/2605.15208}
}
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