Transformer Copilot: Learning from The Mistake Log in LLM Fine-tuning
Authors: name: Jiaru Zou, name: Yikun Ban, name: Zihao Li, name: Yunzhe Qi, name: Ruizhong Qiu, name: Ling Yang, name: Jingrui He

Large language models are typically adapted to downstream tasks through
supervised fine-tuning on domain-specific data. While standard fine-tuning
focuses on minimizing generation loss to optimize model parameters, we take a
deeper step by retaining and leveraging the model's own learning signals,
analogous to how human learners reflect on past mistakes to improve future
performance. We first introduce the concept of Mistake Log to systematically
track the model's learning behavior and recurring errors throughout
fine-tuning. Treating the original transformer-based model as the Pilot, we
correspondingly design a Copilot model to refine the Pilot's inference
performance via logits rectification. We name the overall Pilot-Copilot
framework the Transformer Copilot, which introduces (i) a novel Copilot model
design, (ii) a joint training paradigm where the Copilot continuously learns
from the evolving Mistake Log alongside the Pilot, and (iii) a fused inference
paradigm where the Copilot rectifies the Pilot's logits for enhanced
generation. We provide both theoretical and empirical analyses on our new
learning framework. Experiments on 12 benchmarks spanning commonsense,
arithmetic, and recommendation tasks demonstrate that Transformer Copilot
consistently improves performance by up to 34.5%, while introducing marginal
computational overhead to Pilot models and exhibiting strong scalability and
transferability.