Principal AI Engineer

Oliver Bernard; Greater London; Hybrid; GBP 198,000 - 242,000; Full time

Job summary

Oliver Bernard is hiring a Principal AI Engineer in London, hybrid, to own end-to-end model training, post-training, RL, evaluation and agent infrastructure. This is a hands-on individual contributor role with significant influence over technical direction and core systems.

The role demands strong experience with LLM training and production-grade AI, plus excellent software engineering skills (Python) and a track record of solving hard AI problems in top labs or high-bar startups.

Qualifications

• Experience with LLM training, post-training, RL or evaluation.
• Excellent software engineering fundamentals, ideally Python.
• Track record of solving difficult AI problems in production.

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.

Skills

LLM training

RL/evaluation

Python

Production-grade AI

Senior IC level

Education

Master's or PhD in CS/ML/Math

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.