Senior AI Engineer

We are hiring a Senior AI Engineer to help shape our AI systems and technical direction. You'll lead the design and delivery of complex, production-grade AI solutions - combining machine learning, LLMs, and robust engineering practices to build high-impact products.

We are a team of builders, focused on systems that work reliably in production, not just prototypes. We use modern AI tools extensively, enabling engineers to operate at a higher level - focusing on architecture, system design, and delivering meaningful product impact.

What you'll be doing

• System Design & Ownership: design and lead end-to-end AI systems, from problem framing through to production deployment and iteration.

• Advanced AI Systems & Agents: architect complex agent-based workflows, tool ecosystems, and multi-step reasoning systems.

• Model Strategy: make decisions on model selection, fine-tuning, and when to use ML vs LLM vs hybrid approaches.

• Evaluation & Quality: define evaluation frameworks, metrics, and feedback loops to ensure reliability and continuous improvement.

• Production Excellence: ensure systems are scalable, observable, and robust in real-world environments.

• Technical Leadership: mentor other engineers, review designs, and raise the bar for engineering and AI practices across the team.

• AI-Assisted Engineering: drive effective use of AI tooling within the team, improving productivity without compromising quality.

• Cross-Functional Impact: work closely with product and leadership to shape what we build and why.

• Experience: 5+ years building and deploying ML or AI systems, with significant experience in production environments.

• Strong System Design Skills: ability to design end-to-end AI systems and make sound architectural decisions.

• Deep AI Expertise: strong experience with LLM systems (agents, tool use, evals) and/or traditional ML where appropriate.

• Pragmatism: ability to choose the right approach for the problem, balancing complexity, performance, and cost.

• Evaluation Mindset: experience designing and using evals to drive system improvements.

• Engineering Excellence: high standards for code quality, testing, and maintainability.

• Leadership & Mentorship: experience guiding other engineers and influencing technical direction.

• AI-Native Workflow: strong ability to leverage AI-assisted development tools effectively and thoughtfully.

Competitive salary of £80,000 to £90,000 depending on experience

️ 27 days of annual leave (including 3 days Christmas closing) which increases up to 3 days based on tenure, with the option to roll over, buy or sell up to 3 days

Hybrid working with two days a week from our dog-friendly Hoxton office

On-site gym and cycle to work scheme

️ Employee discount at over 100 retailers

Comprehensive private medical & dental cover with Vitality

Enhanced parental leave pay

Learning & development culture - £1,000 personal annual budget

We're carbon-neutral and are working towards ambitious carbon reduction goals

Lots of team socials & activities

️ Annual team retreat

Want to learn more?

• About us
• Xelix blog
• Xelix news
• Xelix glassdoor

We believe that people from diverse backgrounds, with different identities and experiences make our company and product better. No matter your background, we'd love to hear from you! And if you have a disability, please let us know if there's any way we can make the interview process better for you - we're happy to accommodate!

If you're a recruiting agency - we have an existing list of agencies we work with if required and we are not currently planning on expanding the list. Neither the Talent team nor hiring managers or the Support team will respond to cold outreach.

This is a full-time position, with standard working hours from 9:00 AM to 6:00 PM, Monday through Friday.

Interview Process While the exact process may vary slightly depending on the role, our typical interview stages are:

• Introductory Call - A short Teams conversation with a Talent Partner to discuss your background and the opportunity.
• Hiring Manager Interview - A 30-45 minute Teams meeting to explore your experience and fit for the team.
• Technical Task or Presentation - A role-relevant exercise to demonstrate your skills and approach.
• Final On-site Interview - An in-person meeting with our senior leadership team and co-founders at our office.

At Xelix, we work with some of the world's largest companies to automate and strengthen their financial controls. Our AI solutions redefine how Accounts Payable teams operate - moving from manual processes to automated, intelligent workflows. Xelix is a fast-paced scale-up - things move fast and expectations are high. We raised our Series B with Insight Partners in June 2025 and are expanding aggressively. We have a team 150 talented people pulling together to achieve our goals. Everyone is trusted to take ownership, move fast and have a meaningful impact. We prioritise personal and professional growth, keep things fun, and love to celebrate a milestone together. In this role you'll grow, be challenged and help shape the future of Xelix. If you're excited about building something special with us, we'd love to hear from you.