arXiv Computation and Language

The First Token Is a Clue: Verbalizing Multi-Token Concepts from the J-lens

arXiv Machine Learning
Aug 7

PoolBench: A Benchmark for Pooling Strategies in Concept Representation Evaluation for Decoder-Only LLMs

arXiv:2608. 05162v1 Announce Type: cross Abstract: Pooling is a consequential but under-examined design choice in decoder-only concept representation work: practitioners must collapse token-level hidden states into a passage-level vector, yet no shared protocol exists for comparing this choice across concepts, models, and tasks.

By Ayushi Agarwal
arXiv AI
Jul 17

In-Place Tokenizer Expansion for Pre-trained LLMs

arXiv:2607. 15232v1 Announce Type: cross Abstract: A tokenizer fixed at the start of pre-training allocates vocabulary in proportion to the pre-training corpus, reflecting the deployment priorities at that time.

By Jimmy T. H. Smith, Tarek Dakhran, Alberto Cabrera, Simon S. Lee, Paul Pak, Aditya Tadimeti, Tim Seyde, Maxime Labonne, Alexander Amini, Mathias Lechner
arXiv Computation and Language
Aug 27

SimLens for Early Exit in Large Language Models: Eliciting Accurate Latent Predictions with One More Token

SimLens is a training‑free decoder that improves early‑layer predictions in large language models by keeping only the start token and a candidate answer token and performing a lightweight continuation through the remaining layers. It outperforms direct linear readouts, yielding higher accuracy on tasks such as ARC, BoolQ, and HeadQA with LLaMA‑7B and Vicuna‑7B. The method is extended to Linear SimLens for confidence estimation and combined into SimExit, a hybrid early‑exit mechanism that achieves significant speedups while maintaining accuracy.

By Ming Ma, Bowen Zheng, Zhongqiao Lin, Tianming Yang
arXiv AI
1d ago

Sparse Readout Prism: Explaining Logit-Lens Scores in Features Instead of Tokens

The paper introduces Sparse Readout Prism (SRP), a method that decomposes a language model’s readout matrix into sparse features, allowing logit‑lens scores to be expressed as sums of feature contributions. SRP reveals that lens readings depend on the corpus used to fit the readout, a phenomenon called corpus conditionality, and that the dominant readout feature remains stable across different corpora. By replacing the original readout with SRP’s sparse approximation, the authors recover 8.9–17.3 percentage points more of the tested logit differences than six geometric‑relation baselines, and ablating features shifts logit differences proportionally to their SRP contributions.

By Matteo He, William F. Shen, Xinchi Qiu, Nicholas D. Lane