Neel Nanda et al. reverse-engineer grokking, showing it emerges in three continuous phases

burny_tech · x · 2026-11-01

In this mechanistic interpretability paper, Neel Nanda and colleagues fully reverse-engineer the algorithm a small transformer learns on modular addition: it uses discrete Fourier transforms and trig identities to turn addition into rotation on a circle, verified via activation/weight analysis and Fourier-space ablations. They define continuous progress measures that split training into memorization, circuit formation, and cleanup phases — showing grokking is not a sudden shift but the gradual amplification of structured mechanisms followed by removal of memorizing components.

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