Principal AI Engineer

Oliver Bernard; Greater London; Hybrid; GBP 132,000 - 220,000; Full time

Benefits offered by this job

Equity

Job summary

Oliver Bernard is seeking a Principal AI Engineer in London to own model training, post-training, RL, evaluation and agent infrastructure. This hands-on IC role offers influence over technical direction and requires strong production AI experience.

You will lead end-to-end AI initiatives, build pipelines for training and fine-tuning, develop evaluation systems and agent harnesses, and set direction while staying close to code and models.

Qualifications

• Experience with LLM training, post-training, RL or evaluation in production.
• Strong software engineering fundamentals; Python preferred.
• Track record of solving difficult AI problems in production.
• Experience in top-tier AI labs or high-bar startups; STEM degree required.
• 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 to production.
• Set technical direction while remaining close to code and models.

Skills

LLM training/post-training/RL/eval

Education

STEM degree in CS/ML/Math

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.