PEANuT: Parameter-Efficient Adaptation with Weight-aware Neural Tweakers

Introduction

PEANuT is a PEFT method that introduces a weight-aware neural tweaker to generate adapter updates from the base weight itself. Instead of directly learning a low-rank decomposition Delta W = A @ B as in LoRA, PEANuT transforms the target layer weight through a small neural network (the neural tweaker) to produce Delta W.

PEANuT is built on three key ideas:

• Weight-aware adaptation: Delta W is produced by transforming the base weight using A, B, and optional intermediate layers. Because PEANuT applies A on the output dimension of the base weight, A has shape (out_features, r) instead of LoRA's typical (in_features, r). When in_features > out_features, PEANuT can use fewer parameters than LoRA at the same rank.
• Non-linearity inside the tweaker: PEANuT inserts activation functions in the neural tweaker (default: relu) to increase expressiveness.
• Depth capacity increase: Besides mandatory A and B, PEANuT can insert intermediate r x r layers in residual encoder/decoder pairs. Here, depth counts the number of residual pairs, so depth=0 means only A and B.

Quick start

With respect to your standard PEFT training procedure with LoRA, simply swap your LoraConfig for a PeanutConfig.

import torch
from datasets import load_dataset
from transformers import AutoModelForCausalLM, AutoTokenizer
from trl import SFTConfig, SFTTrainer

from peft import PeanutConfig

model = AutoModelForCausalLM.from_pretrained("meta-llama/Llama-3.2-3B", dtype=torch.bfloat16, device_map="auto")
tokenizer = AutoTokenizer.from_pretrained("meta-llama/Llama-3.2-3B")
dataset = load_dataset("timdettmers/openassistant-guanaco", split="train")
peanut_config = PeanutConfig()

trainer = SFTTrainer(
    model=model,
    train_dataset=dataset,
    processing_class=tokenizer,
    peft_config=peanut_config,
    args=SFTConfig(
        max_length=2048,
        dataset_text_field="text",
        per_device_train_batch_size=2,
    ),
)
trainer.train()
trainer.model.save_pretrained("peanut-llama-3.2-3b")

Run the finetuning script simply by running:

python examples/peanut_finetuning/peanut_finetuning.py --base_model meta-llama/Llama-3.2-3B --data_path timdettmers/openassistant-guanaco

Use the model on Hugging Face

You can load and use the model as any other Hugging Face model.

import torch
from peft import PeftModel
from transformers import AutoModelForCausalLM

model = AutoModelForCausalLM.from_pretrained(
    "meta-llama/Llama-3.2-3B", dtype=torch.bfloat16, device_map="auto"
)
peft_model = PeftModel.from_pretrained(model, "peanut-llama-3.2-3b")

Additional Notes

• r controls the hidden rank of the neural tweaker. Larger r increases capacity and trainable parameters.
• depth controls the number of intermediate encoder/decoder residual pairs. It must be a non-negative integer.
• depth=0 means only A and B.
• depth=1 adds one encoder/decoder residual pair between A and B.
• Larger depths add more r x r residual pairs.
• act_fn controls the non-linearity inside PEANuT and defaults to relu.
• scaling is a direct scalar multiplier on the adapter output before it is added to the frozen base layer output.
• PEANuT can perform better than LoRA across a range of tasks. We also find it strong in very low-parameter regimes (for example around 0.2M trainable parameters).
• Compared with LoRA, PEANuT typically uses more GPU memory and runs slower because it explicitly constructs Delta W during forward passes. Adding intermediate layers (higher depth) increases this overhead further.

Citation

@misc{zhong2025peanutparameterefficientadaptationweightaware,
      title={PEANuT: Parameter-Efficient Adaptation with Weight-aware Neural Tweakers}, 
      author={Yibo Zhong and Haoxiang Jiang and Lincan Li and Ryumei Nakada and Tianci Liu and Linjun Zhang and Huaxiu Yao and Haoyu Wang},
      year={2025},
      eprint={2410.01870},
      archivePrefix={arXiv},
      primaryClass={cs.LG},
      url={https://arxiv.org/abs/2410.01870}, 
}