Principal AI Engineer

Oliver Bernard; Greater London; Hybrid; GBP 180,000 - 220,000; Full time

Job summary

Oliver Bernard is seeking a Principal AI Engineer to take ownership across model training, post-training, RL, evaluation and agent infrastructure in London with hybrid onsite presence.

This hands-on IC role offers significant influence over technical direction and requires a track record at principal or senior IC level in AI research environments.

Qualifications

• Experience with LLM training, post-training, RL or evaluation.
• Strong Python programming skills and solid software engineering fundamentals.
• Proven track record of solving difficult AI problems in production.
• Experience in a top-tier AI lab, tech company or high-bar startup.
• Strong academic background in CS, ML, Mathematics or related STEM field.
• Evidence of operating at Principal or senior IC level.

Responsibilities

• 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 production.
• Set technical direction while remaining close to code and models.

Skills

LLM training

Post-training

RL

Evaluation

Python

Production AI problems

Education

CS/ML/Math degree

Tools

Python

Job description

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.

Responsibilities

• 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

Requirements

• 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 within 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

Location

London, typically 2 days per week onsite.

Package

Up to £220,000 base + meaningful equity.