Principal AI Engineer

Principal AI Engineer | Up to £220k + Equity | London, Hybrid

We’re working with a well‑funded frontier AI company building the systems used to train, evaluate and improve advanced AI agents.

They’re hiring a Principal AI Engineer to take ownership across model training, post‑training, RL, evaluation and agent infrastructure. This is a hands‑on IC role with real influence over technical direction.

• Lead major AI and research‑engineering initiatives end to end
• Build and improve training, fine‑tuning and post‑training pipelines
• Develop evaluation systems, agent harnesses and feedback loops
• Own technically ambiguous problems from experimentation through to production
• Set technical direction while remaining close to code and models

• Strong experience with LLM training, post‑training, RL or evaluation
• Excellent software engineering fundamentals, ideally Python
• Track record of solving difficult AI problems in production
• Experience with in a top‑tier AI lab, technology company or high‑bar startup
• Strong academic background in Computer Science, ML, Mathematics or a related STEM field
• Evidence of operating at Principal or equivalent senior IC level

London, typically 2 days per week onsite.

Up to £220,000 base + meaningful equity.