Senior AI Engineer: LLMs, RL & Agentic Systems

Oliver Bernard; Greater London; On-site; GBP 90,000 - 130,000; Full time

Job summary

Oliver Bernard is partnering with a stealth-mode start-up in London at the forefront of AI research to hire a Senior AI Engineer. You will tackle challenging problems across LLMs, reinforcement learning, and agentic systems.

This hands-on role combines research and engineering: training and fine-tuning models, evaluating progress, building AI agents, and advancing core AI research while maintaining strong software practices in Python.

Qualifications

• Experience with LLMs or foundation models.
• Experience training, fine-tuning, RL or post-training.
• Background in model evaluation and optimisation.
• Experience building AI agents or agentic systems.
• Strong software engineering fundamentals (Python).

Responsibilities

• LLM training & fine-tuning, including reinforcement learning and post-training.
• Evaluation & feedback loops — building systems to continuously assess and optimise models.
• Agent development — designing and building sophisticated AI agents.
• AI research — exploring LLM training, RL, evaluation and optimisation techniques.
• Software engineering — strong engineering fundamentals are essential (Python).

Skills

LLMs / foundation models

Training / Fine-tuning

Reinforcement learning

Model evaluation / optimisation

AI agents / agentic systems

Python

Job description

Oliver Bernard is partnering with a stealth-mode start-up in London at the forefront of AI research to hire a Senior AI Engineer. You will tackle challenging problems across LLMs, reinforcement learning, and agentic systems.

This hands-on role combines research and engineering: training and fine-tuning models, evaluating progress, building AI agents, and advancing core AI research while maintaining strong software practices in Python.