Senior Data Scientist – AI Security Models

About the role

Refractal is an AI security company building the infrastructure organisations need to defend against autonomous AI threats. It works with governments and organisations that cannot afford to get security wrong, and is growing its team. You will own the machine-learning models behind Refractal's detections in production, which decide in milliseconds whether an action is safe, and the analysis that shows how well they perform for each customer.

Key responsibilities

• Train, tune and ship classifiers for prompt injection, data exfiltration, policy violations and other risky AI activity.
• Design low-latency models, including distilled and small models and rules-plus-ML ensembles.
• Analyse production telemetry for drift, blind spots, false-positive cost and new attack patterns.
• Build evaluations and benchmarks for detection models and work with security researchers to turn new attacks into training data.
• Turn company policies and regulatory requirements into measurable controls.

Required profile

• 5+ years in applied ML or data science, with models shipped to production.
• Hands-on NLP and LLM work: fine-tuning, embeddings, classification and LLM-as-judge.
• Experience measuring fuzzy problems, including labelling, agreement and drift.
• Clear communication of trade-offs to engineers and customers.
• Nice to have: experience with adversarial ML, safety or content-moderation models; Montenegrin, Serbian, Bosnian or Croatian.

Required skills

• Strong Python, PyTorch or similar.
• Solid statistics for model evaluation.

What we offer

• Salary of €35,000 to €85,000 gross per year.
• Competitive equity, pension contribution, private medical and dental cover.
• Visa and relocation support.