The paper investigates the dual roles of hidden channels in transformer MLPs, treating each channel as a reader that decides when to respond and a writer that determines what to add back to the residual stream. By examining the joint Jacobian of the MLP’s update, the authors identify a signed pairing coordinate that reveals a small core of strongly coupled reader–writer pairs, often with opposing signs. This opposed core appears early in training and persists across models, influencing how channels contribute to later layers and affecting the model’s output distribution.
By Giyeong Oh, Sunghee Ahn, Youngjae Yu
arXiv:2608. 12447v1 Announce Type: new Abstract: Trained transformer models develop privileged bases: coordinate axes whose statistics differ from the rest of the residual stream.
By Nelson Guda
The paper investigates when a language model actually learns task information versus when its readout (unembedding matrix) learns to express that information. Using a new parameter‑trajectory cross‑coding method, the authors find that hidden states can encode task data early in training, but the readout reorganizes only in a narrow window (0.4–1.1% of Pythia’s pretraining). By varying the readout learning rate, they show that faster readout learning reduces the gap between hidden‑state encoding and output expression without affecting final performance.
By Matteo He, William F. Shen, Alex Iacob, Andrej Jovanovic, Xinchi Qiu, Nicholas D. Lane
arXiv:2608. 05136v1 Announce Type: new Abstract: Gradient descent on a factored model $W = UV^\top$ is implicitly biased toward low-rank solutions, while Adam, starting from the same small initialization, is not.
By Devender Singh
arXiv:2606. 31963v1 Announce Type: new Abstract: Modern LLM workflows move coordinate-indexed objects across checkpoints: steering vectors, sparse autoencoders, top-$k$ neuron sets, attribution lists, and merge alignments.
By John Sweeney
The paper investigates which parts of a low‑rank adaptation (LoRA) update actually drive behavior in language models. It shows that behaviorally effective LoRA writes are sparse, structured, and highly concentrated, with only a few module‑wise components carrying most of the signal. Using a learned‑basis continuation recipe, the authors demonstrate that these sparse, structured writes can be recovered with minimal error and that they remain robust across different training continuations and evaluation tasks.
By Haruto Sato, Yuki Tanaka, Ren Nakamura, Aoi Kobayashi, Mei Ito