Transformer-based large language models (LLMs) have advanced significantly, but they remain opaque in terms of how they process tasks.Understanding LLMs involves tracing their internal logic, treating neurons as the basic computational unit.A 'circuit' in LLMs is defined as a sequence of feature activations and connections used to transform input into output.To trace feature activations, a replacement model using transcoders is employed in place of MLP blocks in transformer models.Cross-layer transcoders (CLT) capture effects across multiple layers, aiding in circuit tracing.An attribution graph is built from the replacement model, showing the computational path with feature interpretability.Researchers used attribution graphs to understand how models plan ahead in tasks like poem generation.While circuit tracing is a significant step towards interpretability, limitations remain in understanding global circuits and inactive features.This approach provides insight into how LLMs generate text, aiding in alignment, safety, and trust in AI systems.Circuit tracing marks a crucial milestone on the journey to achieving true interpretability in large language models.