Engineering

Senior ML Engineer

Sofia, BulgariaFull-time

Zeta Cortex is a company building software that secures enterprise agentic AI, giving organizations control over what their AI agents are allowed to do.

As a Senior ML Engineer you'll build the models at the core of that work, from training data to production, in a small team where you own problems end to end.

What you'll do

  • Build and maintain training and evaluation datasets from real-world security data.
  • Fine-tune and evaluate open-weight language models for security classification tasks.
  • Design offline evaluations and regression checks so every model change is measurable.
  • Take models to production under tight latency and reliability requirements.
  • Build feedback loops that turn human review into better training data.
  • Work closely with the engineers building our platform, from backend integration to how model results reach users.

What you bring

  • Hands-on experience fine-tuning and evaluating open-weight language models, and taking at least one to production.
  • Strong Python and the usual stack (PyTorch, Hugging Face), and comfort working in a production codebase.
  • Experience turning messy real-world data into reliable datasets.
  • A security mindset: you've thought about how an attacker would get around a classifier.
  • You like owning a problem end to end in a small team.

Nice to have

  • Security ML background, such as malware, intrusion or fraud detection, or adversarial ML.
  • Low-latency inference experience: quantization, vLLM, ONNX Runtime or llama.cpp.
  • Familiarity with AI agent frameworks, MCP or tool-calling models.
  • Go or Rust.

Why Zeta Cortex

  • An urgent problem: enterprises are giving AI agents real access to their systems.
  • Hard, real-world security problems rather than benchmarks.
  • Real ownership in a small team.
  • Work closely with top experts in the field and learn a lot along the way.
  • Work at the edge of technology and innovation in a field that's still being defined.

How to apply

Email careers@zetacortex.ai with your CV or GitHub and a few lines about a model you've taken to production: what it did, how you evaluated it and what you'd do differently.