Maksym Del

I study the limitations of language models, especially reasoning models, and how to make their deployment more reliable. My work spans uncertainty estimation, capability evaluation, chain-of-thought monitoring, and interpretability. I am a Research Fellow at EXAI and the University of Tartu, where I completed my PhD in Artificial Intelligence.

Portrait of Maksym Del

Research

Sampling-efficiency curves for confidence estimation across reasoning models and benchmarks

How Uncertainty Estimation Scales with Sampling in Reasoning Models

Maksym Del, Markus Kängsepp, Marharyta Domnich, Ardi Tampuu, Lisa Yankovskaya, Meelis Kull, Mark Fishel

Preprint, 2026

We show that combining verbalized confidence and self-consistency with two samples improves AUROC by up to 12 points on average, outperforming either signal alone even at larger sampling budgets.

Overview of an LLM-based pipeline for artificial error generation and grammatical error correction

To Err Is Human, but Llamas Can Learn It Too

Agnes Luhtaru*, Taido Purason*, Martin Vainikko, Maksym Del, Mark Fishel

Findings of EMNLP, 2024

* Equal contribution.

We generate human-like errors with language models and use them to train grammatical error correction systems, improving the previous state of the art across German, Ukrainian, and Estonian.

Cover of Maksym Del's PhD thesis on multilingual and multi-domain transformer representations

Multilingual and Multi-Domain Representational Patterns Across Transformer-Based Models

Maksym Del

PhD thesis, University of Tartu, 2024

This thesis examines how transformer models organize languages and domains internally, including where shared representations emerge and where they remain fragmented.

Illustration for the True Detective abductive-reasoning benchmark

True Detective: A Deep Abductive Reasoning Benchmark Undoable for GPT-3 and Challenging for GPT-4

Maksym Del, Mark Fishel

*SEM, 2023

We introduce a 191-puzzle benchmark exposing a major limitation in abductive reasoning: then-frontier GPT-4 scored 38%, versus over 80% for top human solvers.

Layer-wise cross-lingual similarity patterns in multilingual language models

Cross-lingual Similarity of Multilingual Representations Revisited

Maksym Del, Mark Fishel

AACL, 2022

Oral presentation.

We introduce Average Neuron-Wise Correlation (ANC), reducing the required neuron-wise comparisons from O(N²) to O(N), and show that multilingual models first align languages before specializing for prediction.

Cross-lingual sentence representation similarities for Baltic and other languages

Similarity of Sentence Representations in Multilingual LMs: Resolving Conflicting Literature and a Case Study of Baltic Languages

Maksym Del, Mark Fishel

Baltic Journal of Modern Computing, 2022

We resolve conflicting findings about multilingual representations and show that most languages, including low-resource Baltic languages, share a cross-lingual space, while a few remain separate.

Visualization of domain structure in neural machine translation representations

Translation Transformers Rediscover Inherent Data Domains

Maksym Del*, Elizaveta Korotkova*, Mark Fishel

WMT, 2021

* Equal contribution.

We show that translation models recover latent data domains, then reuse their representations for unsupervised adaptation, avoiding a separate language model and improving in-browser English-to-Estonian translation by up to 1.6 BLEU.

Zero-shot monolingual translation setup for grammatical error correction and style transfer

Grammatical Error Correction and Style Transfer via Zero-shot Monolingual Translation

Elizaveta Korotkova, Agnes Luhtaru, Maksym Del, Krista Liin, Daiga Deksne, Mark Fishel

Preprint, 2019

We use a single multilingual translation model for grammatical error correction and style transfer, without task-specific training data.

Phrase-based unsupervised machine translation with compositional phrase embeddings

Phrase-based Unsupervised Machine Translation with Compositional Phrase Embeddings

Maksym Del, Andre Tättar, Mark Fishel

WMT, 2018

We propose compositional phrase embeddings for phrase-based unsupervised machine translation.

Architecture and results of the C-3MA neural machine translation systems

C-3MA: Tartu-Riga-Zurich Translation Systems for WMT17

Matīss Rikters, Chantal Amrhein, Maksym Del, Mark Fishel

WMT, 2017

We describe the University of Latvia, University of Zurich, and University of Tartu neural machine translation systems submitted to the WMT17 shared task.