Arthur Renard

Machine-learning researcher
Founding engineer, Xent Labs
Lausanne, Switzerland

I teach language models to improve themselves, with reinforcement learning and with games.

John Tenniel’s engraving of the Caterpillar smoking a hookah on a mushroom, with Alice looking up at him.
John Tenniel, “Advice from a Caterpillar”, 1865

‘Who are you?’
said the Caterpillar.

An applied mathematician, mostly. I work on reinforcement learning for self-improving language models.

Originally from Belgium, I moved to Switzerland to study mathematics at EPFL and applied mathematics at ETH Zürich, with a year at KTH in Stockholm in between.

Today I am a founding engineer and ML researcher at Xent Labs, where we develop Xent Games: an open-ended space of games for language models that produces measurable signals on reasoning, anticipation and cooperation.

Outside research, I’ve also built the website and mobile app for Festival Balélec, Europe’s largest student festival.

2022 to 2024
ETH Zürich — MSc Applied Mathematics. Statistics and deep learning; thesis on symbolic regression with transformers for math-olympiad problems.
2021 to 2022
KTH, Stockholm — Exchange year, Applied Mathematics.
2019 to 2022
EPFL, Lausanne — BSc Mathematics.

Symbolic regression · Mathematical reasoning · Generative models · LLM training & evaluation · Reinforcement learning · Artificial life

French · English · German (intermediate)

Research

‘Curiouser and curiouser!’ cried Alice.

Van Gogh’s Allée des Alyscamps: a road of orange leaves running between two walls of tall yellow poplars, a few walkers on it.
Vincent van Gogh, L’Allée des Alyscamps, 1888. “Two roads diverged in a yellow wood”

I.

Preprint · 2026

Cross-Entropy Games and Frost Training

A method that uses reward gradients in embedding space to accelerate GRPO training on Cross-Entropy Games.

LLMs · GRPO · Reinforcement learning

arXiv

Nineteenth-century phrenology bust of Dr Spurzheim, the skull divided into labelled faculties.
Phrenological bust of Dr Spurzheim, 19th c., Library of Congress

II.

Preprint · 2026

Cognitive Training for Language Models

A principled framework for relevant skill discovery in language models via Cross-Entropy Games: a curriculum of tasks that develops general capabilities.

LLMs · Curriculum learning · Optimization

arXiv

Leibniz’s handwritten table of powers of two written in binary.
G. W. Leibniz, binary table, manuscript c. 1697

III.

AI for Math Workshop · ICML 2025

Boolformer

A Transformer for symbolic regression of Boolean functions: it reads a truth table and writes down a compact formula, robust to noisy and partial data.

Transformers · Symbolic regression · Interpretable ML

arXivCode

A Lenia colony, its parameter swept back and forth across the edge between dying out and spreading everywhere

IV.

GECCO Companion · 2024

Phase Transition Finder

An algorithm that locates parameters on the border between phases of high-dimensional dynamical systems. Applied to Lenia, it doubles the frequency of interesting emergent behaviours.

Complex systems · Artificial life · PyTorch

arXivCode

Xent Labs · since 2025

We build Xent Games: an open-ended space of games that language models play to get better, and that tell us how well they reason, anticipate and cooperate. Croquet with flamingos, more or less.

Rubik’s cube, Pong, Space Invaders, Simon, Pac-Man, Game Boy and friends, credited below

Side projects

‘It’s always tea-time.’

NASA, the Lunar Grand Prix, Apollo 16, 1972

2026 · Three.js · MediaPipe · Blender

Super Claude Bros

Hand-controlled games: four finger-gun shooters and a kart racer steered with an invisible wheel.

PlayCode

Strudelify playing Smells Like Teen Spirit, Californication, Space Oddity, Fortunate Son, Starman…

2026 · Strudel · MIDI · TypeScript

Strudelify

Type a song name, get an editable instrumental loop in Strudel. Compiled from open transcriptions, no LLM involved.

Try itCode

Me, generated with Fluxtuning

2025 · FLUX.1 · LoRA · Flow matching

Fluxtuning

A practical write-up on fine-tuning FLUX.1-dev with LoRA for personalised image generation.

ReadCode

The Grande Scène of Festival Balélec

2024 · Next.js · TypeScript · Strapi

Festival Balélec

Designed and built the official website and mobile app for the 2024 edition of Europe’s largest student festival, attended by more than 15,000 people.

Visit

Experience

‘Would you tell me, please, which way I ought to go from here?’

Tenniel’s engraving of Alice looking up at the Cheshire Cat sitting in a tree.
John Tenniel, “Pig and Pepper”, 1865

  1. Since 2025

    Xent Labs

    Founding engineer & ML researcher · Lausanne

    Building Xent Games, an LLM-native game space designed to train and evaluate reasoning, anticipation and cooperation in language models.

  2. 2023 to 2025

    EPFL

    Researcher, Chair of Statistical Field Theory · Lausanne

    Symbolic methods and deep learning: Boolformer (AI for Math Workshop, ICML 2025) and the Phase Transition Finder (GECCO Companion 2024), under Prof. Clément Hongler.

  3. 2023 to 2024

    Festival Balélec

    Web & app lead, volunteer · Lausanne

    Designed and built the website and mobile app for Europe’s largest student festival, more than 15,000 attendees.

Tenniel’s engraving of the grinning Cheshire Cat in a tree.

Wish you were here.

‘We’re all mad here.’

arthurenard@icloud.com

John Tenniel, the Cheshire Cat vanishing, 1865