arXiv Computation and Language

Weighted Ensemble Sampling for Rare-Event Estimation in Language Models

arXiv Machine Learning
Sep 30

Quantifying Behavioral Tails in Black-Box Language Models

The paper introduces RareTrap, a framework that estimates the probability of severe behaviors in black‑box large language models. RareTrap constructs a geometry‑aware mapping from a low‑dimensional latent space into token‑embedding space using a surrogate LLM, creating an explicit and reproducible distribution over input prompts. By applying a response‑level performance function and sequential rare‑event simulation, RareTrap concentrates evaluations on increasingly severe behaviors while preserving probability, enabling estimation of such behaviors with as few as 200 evaluations across multiple open‑weight and frontier models.

By Elsayed Eshra, Ali Al-Lawati, Dongwon Lee, Suhang Wang
arXiv Machine Learning
Aug 4

The Illusion of Stochasticity in LLMs

arXiv:2604. 06543v2 Announce Type: replace-cross Abstract: In this work, we demonstrate that reliable stochastic sampling is a fundamental yet unfulfilled requirement for Large Language Models (LLMs) operating as agents.

By Xiangming Gu, Soham De, Michalis Titsias, Larisa Markeeva, Petar Veli\v{c}kovi\'c, Razvan Pascanu
arXiv Machine Learning
Jul 22

Estimating near-verbatim extraction risk in language models with decoding-constrained beam search

arXiv:2603. 24917v2 Announce Type: replace-cross Abstract: Recent work shows that standard greedy-decoding extraction methods for quantifying memorization in LLMs miss how extraction risk varies across sequences.

By A. Feder Cooper, Mark A. Lemley, Christopher De Sa, Lea Duesterwald, Allison Casasola, Jamie Hayes, Katherine Lee, Daniel E. Ho, Percy Liang
arXiv Computation and Language
Aug 28

Stochastic Estimation of Transduced Language Models

Transduced language models (TLMs) combine a pretrained source language model with a finite‑state transducer to produce a language model over target strings. The paper introduces an unbiased stochastic estimator that resamples source prefixes without replacement and reweights them, allowing accurate estimation of target prefix probabilities while reducing computation compared to threshold‑pruned beam summing. Experiments on encyclopedic text, DNA, and DNA‑to‑amino‑acid transduction show improved compute–variance trade‑offs and significant runtime reductions, and the method also lowers estimated corpus surprisal in a reading‑time analysis without altering its conclusions.

By V\'esteinn Sn{\ae}bjarnarson, Samuel Kiegeland, Manuel de Prada Corral, Ryan Cotterell, Tim Vieira
arXiv Machine Learning
Aug 28

Recipes for Steering and Scaling LLMs via Sampling

The paper introduces a flexible, theoretically grounded framework for steering and scaling autoregressive large language models (LLMs) through sampling. It presents two algorithms—Sequential Monte Carlo (SMC) and Replica Exchange (RE)—that guide generation toward desired distributions such as powering, product, or tilting of the base model. Experiments show these methods outperform Best‑of‑N and standard MCMC baselines, offering a systematic recipe for probabilistic inference with LLMs via sampling.

By Jiajun He, Zongyu Guo, Jos\'e Miguel Hern\'andez-Lobato, Yuanqi Du
arXiv Computation and Language
Sep 1

Beyond the Final Layer: Intermediate Representations for Better Multilingual Calibration in Large Language Models

The paper investigates multilingual confidence calibration in large language models, revealing that non‑English languages are systematically less well calibrated than English. By analyzing internal representations, the authors find that late‑intermediate layers provide a more reliable confidence signal than the final layer, which is biased by English‑centric training. They propose training‑free methods such as Language‑Aware Confidence Ensemble (LACE) to adaptively select optimal layers per language, aiming to improve global equity and trustworthiness of LLMs.

By Ej Zhou, Caiqi Zhang, Tiancheng Hu, Chengzu Li, Nigel Collier, Ivan Vuli\'c, Anna Korhonen