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Pietro Lesci

8 accepted papers

2025

Causal Estimation of Tokenisation Bias

ACL 2025long

Modern language models are typically trained over subword sequences, but ultimately define probabilities over character-strings. Ideally, the choice of the tokeniser—which maps character-strings to subwords—should not affect the probability assigned to the underlying character-string; in practice, i…

2025

PolyPythias: Stability and Outliers across Fifty Language Model Pre-Training Runs

ICLR 2025poster

The stability of language model pre-training and its effects on downstream performance are still understudied. Prior work shows that the training process can yield significantly different results in response to slight variations in initial conditions, e.g., the random seed. Crucially, the research c…

2025

Self-Training Large Language Models for Tool-Use Without Demonstrations

NAACL 2025findings

Large language models (LLMs) remain prone to factual inaccuracies and computational errors, including hallucinations and mistakes in mathematical reasoning. Recent work augmented LLMs with tools to mitigate these shortcomings, but often requires curated gold tool-use demonstrations. In this paper, w…

2024

AnchorAL: Computationally Efficient Active Learning for Large and Imbalanced Datasets

NAACL 2024long

Active learning for imbalanced classification tasks is challenging as the minority classes naturally occur rarely. Gathering a large pool of unlabelled data is thus essential to capture minority instances. Standard pool-based active learning is computationally expensive on large pools and often reac…

2024

Causal Estimation of Memorisation Profiles

ACL 2024long

Understanding memorisation in language models has practical and societal implications, e.g., studying models’ training dynamics or preventing copyright infringements.Prior work defines memorisation as the causal effect of training with an instance on the model’s ability to predict that instance. Thi…

2024

Tending Towards Stability: Convergence Challenges in Small Language Models

EMNLP 2024finding

Increasing the number of parameters in language models is a common strategy to enhance their performance. However, smaller language models remain valuable due to their lower operational costs. Despite their advantages, smaller models frequently underperform compared to their larger counterparts, eve…

2023

Diable: Efficient Dialogue State Tracking as Operations on Tables

ACL 2023findings

Sequence-to-sequence state-of-the-art systems for dialogue state tracking (DST) use the full dialogue history as input, represent the current state as a list with all the slots, and generate the entire state from scratch at each dialogue turn. This approach is inefficient, especially when the number…