RL environment design for computer-use agents. Reward shaping, reward hacking detection, trajectory collection for browser-based tasks.
Mario Brajkovski
Building RL environments and evaluation systems for frontier AI agents
North Macedonia · Remote
Founding engineer at HUD, building RL training environments and evaluation infrastructure for computer-use agents. Co-author of ZeroDayBench (ICLR 2026), a benchmark for evaluating whether LLM agents can autonomously discover and patch zero-day vulnerabilities. Most of my time goes into the infrastructure that makes models better — RL environments, reward design that holds up under hacking, and evals that actually mean something.
What I Work On
Evaluation infrastructure for frontier models. Figuring out what to measure and how to measure it without fooling yourself.
Agent safety and red-teaming. Trying to break autonomous agents before they go to production.
Research
Can frontier LLMs autonomously find and patch real vulnerabilities? We tested GPT-5.2, Claude Sonnet 4.5, and Grok 4.1 on 22 novel critical zero-days in open-source codebases. Short answer: not yet. But the failure modes are telling. A couple of frontier labs are now looking at running it internally.
Privacy-preserving ML using AMD SEV-SNP encrypted VMs. Full memory encryption and attestation with <20% overhead on 110M-param BERT.
Selected Work
RL Training Environments
RL environments for training computer-use agents. Reward hacking analysis and prevention, red-teaming infrastructure, alignment testing.
Evaluation Infrastructure
Eval infrastructure for an unreleased frontier model. Designed the evals from scratch, including the scoring and validation.
Eval environment for AI agents on competitive programming. Anti-cheating grading server, 21 problem scenarios with hidden test cases.
Writing
Projects
AI companion with a Live2D avatar that talks, emotes, and moves in sync with the conversation. Sub-second voice latency, persistent memory.
Background
2019–2025: Infrastructure and reliability engineering at Joyn (streaming platform, 4 yrs) and HanseMerkur (insurance). Distributed systems, large-scale ops.