Explaining Fine Tuned LLMs via Counterfactuals A Knowledge Graph Driven Framework

2025-09-25

AI Summary

The impact of Low-Rank Adaptation (LoRA) fine-tuning on the structural reasoning and semantic behavior of large language models (LLMs) remains poorly understood. Method: We propose CFFTLLMExplainer, the first explainable framework integrating counterfactual reasoning with knowledge graphs. It constructs BioToolKG—a domain-specific heterogeneous knowledge graph in bioinformatics—and introduces a soft masking mechanism to induce minimal structural perturbations that maximize semantic change. Structural sparsity and semantic interpretability are jointly optimized via entropy regularization and edge-smoothing constraints. Results: Evaluated on LoRA-fine-tuned LLaMA models, counterfactual masks precisely identify structural dependencies critical to model behavior, exhibiting strong alignment with actual LoRA parameter updates. This work establishes a novel paradigm for interpreting fine-tuned LLMs—one grounded in theoretical rigor and practical interpretability—advancing both mechanistic understanding and trustworthy deployment of adaptive LLMs.

Technology Category

• Machine Learning: Large Multimodal Models (LMMs)
• Natural Language Processing: (Large) Language Models
• Knowledge Representation and Reasoning: Action, Change, and Causality

Application Category

• Semantics and Knowledge: Methods to enhance, augment, integrate or synergize semantic models such as knowledge graphs and LLMs
• Graph Algorithms and Modeling for the Web: Foundation models and LLMs for Web-related graphs
• Search and Retrieval-Augmented AI: Web learning to rank, online learning, and counterfactual learning for ranking

Abstract

The widespread adoption of Low-Rank Adaptation (LoRA) has enabled large language models (LLMs) to acquire domain-specific knowledge with remarkable efficiency. However, understanding how such a fine-tuning mechanism alters a model's structural reasoning and semantic behavior remains an open challenge. This work introduces a novel framework that explains fine-tuned LLMs via counterfactuals grounded in knowledge graphs. Specifically, we construct BioToolKG, a domain-specific heterogeneous knowledge graph in bioinformatics tools and design a counterfactual-based fine-tuned LLMs explainer (CFFTLLMExplainer) that learns soft masks over graph nodes and edges to generate minimal structural perturbations that induce maximum semantic divergence. Our method jointly optimizes structural sparsity and semantic divergence while enforcing interpretability preserving constraints such as entropy regularization and edge smoothness. We apply this framework to a fine-tuned LLaMA-based LLM and reveal that counterfactual masking exposes the model's structural dependencies and aligns with LoRA-induced parameter shifts. This work provides new insights into the internal mechanisms of fine-tuned LLMs and highlights counterfactual graphs as a potential tool for interpretable AI.

Problem

• Explaining how fine-tuning alters LLMs' structural reasoning and semantic behavior
• Understanding domain-specific knowledge acquisition through LoRA fine-tuning mechanisms
• Developing interpretable AI methods to reveal fine-tuned LLMs' internal mechanisms

Innovation

• Counterfactual explanations using knowledge graphs
• Soft mask learning for minimal structural perturbations
• Joint optimization of sparsity and semantic divergence