DEFT: Decompositional Efficient Fine-Tuning

Introduction

DEFT adapts a frozen weight W by removing a learned rank-r sub-space and injecting a low-rank update in its place: W' = (I - P_proj) @ W + Q_P @ R. Unlike a purely additive update (LoRA's W + B @ A), the removal term lets DEFT re-purpose existing weight directions, which helps it learn new data/concepts while keeping the base model's capabilities (low forgetting). With the default identity initialization the adapter is an exact no-op at the start of training, and the update merges into the base weights for inference.

Quick start

With respect to your standard PEFT training procedure with LoRA, simply swap your LoraConfig for a DeftConfig. DEFT uses alpha for the LoRA-style injection scaling (alpha / r) and decomposition_method ("relu" default, or "qr") to derive the projector.

python

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

model = AutoModelForCausalLM.from_pretrained("meta-llama/Meta-Llama-3-8B", dtype=torch.bfloat16, device_map="auto")
tokenizer = AutoTokenizer.from_pretrained("meta-llama/Meta-Llama-3-8B")
tokenizer.pad_token_id = tokenizer.eos_token_id
deft_config = DeftConfig(r=32, alpha=64, decomposition_method="relu")

peft_model = get_peft_model(model, deft_config)
peft_model.print_trainable_parameters()

dataset = load_dataset("imdb", split="train[:1%]")

training_args = SFTConfig(dataset_text_field="text", max_length=128)
trainer = SFTTrainer(
    model=peft_model,
    args=training_args,
    train_dataset=dataset,
    processing_class=tokenizer,
)
trainer.train()
peft_model.save_pretrained("deft-llama-3-8b")

To utilize the fine-tuned DEFT modules, simply run the following command:

python

import torch
from peft import PeftModel
from transformers import AutoModelForCausalLM

model = AutoModelForCausalLM.from_pretrained(
    "meta-llama/Meta-Llama-3-8B", dtype=torch.bfloat16, device_map="auto"
)
peft_model = PeftModel.from_pretrained(model, "deft-llama-3-8b")

Advanced Usage

By default DEFT is applied to the query and value layers. Adding adapters on more layers will increase memory usage. To choose a different set of layers:

bash

python examples/deft_finetuning/deft_finetuning.py --base_model meta-llama/Meta-Llama-3-8B --target_modules "q_proj,k_proj,v_proj,o_proj"

DEFT supports torch.nn.Linear and Conv1D (e.g. gpt-2) layers. The qr decomposition gives an orthogonal projection, and para=True selects the removal-only PaRa variant.

Fine-tune

bash

python deft_finetuning.py \
    --base_model "PATH_TO_MODEL" \
    --data_path "PATH_TO_DATASET" \
    --output_dir "PATH_TO_OUTPUT_DIR" \
    --batch_size 1 \
    --num_epochs 3 \
    --learning_rate 3e-4 \
    --cutoff_len 512 \
    --val_set_size 500 \
    --eval_step 10 \
    --save_step 100 \
    --device "auto" \
    --rank 32 \
    --alpha 64 \
    --decomposition_method "relu" \
    --deft_dropout 0.05 \
    --target_modules "q_proj,v_proj" \
    --hub_model_id "YOUR_HF_REPO" \
    --push_to_hub

Citation

@article{kumar2026deft,
  title={DEFT: Decompositional Efficient Fine-Tuning for Text-to-Image Models},
  author={Kumar, Komal and Anwer, Rao and Shahbaz Khan, Fahad and Khan, Salman and Laptev, Ivan and Cholakkal, Hisham},
  journal={Advances in Neural Information Processing Systems},
  volume={38},
  pages={102009--102035},
  year={2026}
}