Senior AI Engineer (Machine Learning/Prompt Engineer)

We are a fast-moving technology company and one of the most successful providers of online reward and benefits solutions in the UK. We believe that everyone deserves an exceptional experience at work, every day, and build workplace technology that makes this happen. Benifex’s mission is to build remarkable experiences that employees love. Today, Benifex supports more than five million employees in over 3,000 organisations across more than 100 countries. To help us on our quest to be the best, we need brilliant people on board and that’s where you come in.

Why should you apply?

• Impact: Play a central role in shaping our AI capabilities across our products.
• Tech: Work with Vertex AI, AlloyDB, LangChain, GCP.
• Greenfield: Join a newly formed team working on a product that is used by millions of users around the world.
• Work for a profitable, fast-growing market leader in the online reward and benefits space.

Please note we are unable to offer visa sponsorship and require people to be based in the UK or Ireland for this position.

Tech setup of your choice (MacBook Pro or equivalent, monitors, etc.). Flexible work – choose a working setup that works for you, our only ask is to see you once a quarter in our UK HQ.

Your birthday off. Healthcare cash plan to cover the costs of day-to-day healthcare. Income Protection (75%) and life assurance (4x salary). £50 monthly allowance to spend on whatever takes your fancy; your very own Benifex card will be topped up at the start of each month!

We’re seeking a skilled Generative AI Engineer to join our AI Squad and play a key role in advancing our AI capabilities across Benifex products. You’ll work at the heart of our AI initiatives, partnering with engineers, product managers, and data stakeholders to design and implement AI-powered services that enhance user experience and operational efficiency. You will have the opportunity to make a real difference by ensuring the stability and performance of a platform used by millions. We work in a dynamic environment, where we learn and grow by tackling complex technical challenges.

Responsibilities:

• Design, build, and maintain AI systems and tools using machine learning and large language models (LLMs), with a strong focus on prompt engineering and model fine-tuning.
• Collaborate with cross-functional teams to identify opportunities for AI and automation across the product suite.
• Develop scalable pipelines for data ingestion, model training, evaluation, and deployment.
• Prototype and iterate on prompt designs to maximise the relevance, coherence, and usefulness of LLM outputs.
• Work with cloud infrastructure (GCP preferred) and MLOps tools to deploy, monitor, and manage AI services.
• Contribute to the development of reusable AI components and APIs to support product and internal teams.
• Stay informed of the latest developments in machine learning and generative AI to drive continuous improvement.

What are we looking for?

• Proven experience operating as a senior level engineer within a product or SaaS company.
• Proven experience with Python and ML libraries such as TensorFlow or PyTorch.
• Experience working with LLMs (Gemini), prompt engineering, and reinforcement learning from human feedback (RLHF).
• Experience with LangChain for building LLM applications with RAG pipelines and agent workflows.
• Practical understanding of vector search, embeddings, and retrieval-augmented generation (RAG).
• Experience building and deploying machine learning models into production environments.
• Familiarity with MLOps tools and practices (Vertex AI).
• Understanding of data pipelines, data preparation, and feature engineering.

Bonus Points for:

• Hands-on experience with prompt tuning, fine-tuning LLMs, or adapting open-source models for specific use cases.
• Hands-on experience with AlloyDB or similar.
• Experience working in cloud environments, particularly Google Cloud Platform (GCP).

General engineering traits that we look for:

• A mindset of holding yourself and others accountable, someone who can be relied on in challenging situations, a bias to action.
• Someone who invests in their craft and self-learning, a continuous improvement mindset, a focus on best practices, and someone keen to see how new tools/technology can be applied to business problems.
• Strong opinions loosely held, you're open to ideas, and seek feedback and input from others.
• An effective communicator to technical and non-technical audiences, able to break down complex information into simple to understand language.
• Someone who thrives on solving technical challenges, who has a methodical way to work through problems and offer pragmatic solutions.

Even if you don’t meet all of the requirements for this role, we encourage you to apply! We are looking for talented and passionate individuals who are eager to learn and grow. We also offer a variety of other roles, so please check out our careers page to see if there is something else that might be a good fit for you.

We are an equal opportunity employer and value diversity at our company. We do not discriminate on the basis of race, religion, colour, national origin, gender, sexual orientation, age, marital status, veteran status, or disability status. We are committed to creating a diverse and inclusive workplace where everyone feels welcome and respected. We believe that diversity and inclusion are essential to our success, and we are proud to be an equal opportunity employer.

We are a proud member of the Disability Confident employer scheme. If you require any reasonable adjustments at any stage during the recruitment process, please let us know with your application.