Ilia Zavidnyi

Research engineer · Prague

At JetBrains Research, I develop and evaluate post-training methods for code and reasoning models, with a focus on coding agents and reasoning efficiency. At CIIRC, CTU Prague, I research how vision-language-action policies acquire and retain skills.

Experience

JetBrains

— present

Research Engineer

  • Lead research projects on model-to-model communication, inference optimisation, continual and multi-task learning, and reasoning efficiency.
  • Design and run post-training experiments for code and reasoning LLMs using supervised fine-tuning and reinforcement learning, including distributed RL on 64 H200 GPUs with NeMo-RL.
  • Fine-tuned Mellum, JetBrains’ code-completion model, and designed evaluations on proprietary repositories.
  • Developed Step Rejection Fine-Tuning to learn from failed coding-agent runs: 32.2% SWE-bench Verified resolution vs. 30.9% with rejection fine-tuning.
  • Built data-generation, training, and evaluation pipelines for software-engineering agents.

—

Software Engineer

Including internship

  • Built ML-backed web-element detection for Aqua’s locator completion, later reused in UI test generation.
  • Rebuilt Aqua’s Web Inspector using the Chrome DevTools Protocol; added Cypress support.

CIIRC, Czech Technical University in Prague

— present

External Researcher

I study continual adaptation of vision-language-action (VLA) policies for robotic manipulation: acquiring new skills while retaining existing ones.

I fine-tune π₀.₅ policies using REALM simulation demonstrations and real DROID data, and evaluate in simulation and on hardware. I also research real-time reinforcement learning.

Developed test-time action sampling, filtering, and averaging for π₀-FAST, improving success from 36.5% to 55.5% across eight REALM simulation tasks without retraining.

Tools & methods

Learning
SFT, GRPO / RLVR, distillation, imitation learning, continual learning, VLA fine-tuning
Frameworks & infra
PyTorch, JAX, NeMo-RL, Megatron-LM, multi-node GPU training, Slurm, Kubernetes, Apache Iceberg
Languages
Python, C++, Kotlin / Java, TypeScript, Go

Education

2025 — 2027 (expected)

M.Sc. Cybernetics & Robotics

Czech Technical University in Prague

2020 — 2024

B.Sc. Computer Science

Charles University · Specialization in Artificial Intelligence

Selected publications & manuscripts

Contact

For research engineering roles or collaborations: ilia@zavidnyi.com.