Senior Machine Learning Engineer, Personalisation Office: United Kingdom Remote: UK

At Cleo, we are on a mission to fundamentally change humanity's relationship with money. We imagine a world where everyone has access to a hyper‑intelligent financial advisor in their pocket. Cleo is a profitable, fast‑growing unicorn with over $300 million in ARR and growing over 2 × year‑over‑year.

We have an exceptionally high bar for talent, seeking individuals who are not only at the top of their field but also embody our culture of collaboration and positive impact.

Senior Machine Learning Engineers at Cleo build novel solutions to real‑world problems, such as chatbots to coach users around their financial health, classifiers to better understand transaction data, and optimising transactions within our payments platform. As a Senior Engineer, you will lead technical work within a team of adaptable, creative and product‑focused engineers.

What you'll be doing:

• Join the Machine Learning Growth Personalisation team, working in a cross‑functional squad focused on using ML to personalise the Cleo product.
• Work on recommender systems and/or behavioural modelling (e.g. multi‑armed bandits, uplift modelling and other causal modelling).
• Deploy models into production using our in‑house ML platform, owning the whole process end‑to‑end.
• Collaborate cross‑functionally with backend engineers, data analysts and product managers.
• Identify and lead technical work on problems that were previously unknown or poorly understood, driving change at the chapter level that affects multiple squads.
• Mentor and advise colleagues on choices of models, architecture, and evaluation.

Examples of product feature work our ML Engineers have taken part in over the last year include:

• Built recommender systems for in‑app prompts and notifications.
• Built a multi‑armed bandit testing framework to enable fast and low‑regret multi‑variate testing.
• Built AI agents to explore and derive insights from users’ transactional data.
• Built models to optimise payment success for our customers and optimise costs for the business.
• Developed contextual intent classifiers to understand what conversations users are having with Cleo.
• Built ML models to understand the actions that users have available to them in Cleo and provide those contextually in conversations.
• Built ML models to understand the risk of customers using bank transaction features and user activity.

What you'll need:

• Experience in personalisation (recommender systems and/or behaviour modelling).
• Excellent knowledge of both data science (Python, SQL) and production tools.
• Deep understanding of probability and statistics fundamentals.
• Big‑picture thinking to diagnose problems and productionise research.
• Top‑tier communication skills, to partner with product and commercial leaders.
• Industry‑leading contributions to your field, communicated through conferences, blogs, talks, or open‑source projects.
• Advanced degree in a quantitative discipline or equivalent commercial experience.

Nice to have:

• Strong experience with additional programming languages such as Java, Scala, C++.

The recruitment process:

• Interview with a recruiter (30 min).
• Interview with the hiring manager (30 min).
• Python coding interview (45 min).
• White‑boarding session (60 min).
• Technical discussion (45 min).

What do you get for all your hard work:

• A competitive compensation package (base + equity) with 3‑annual reviews, aligned to our termly OKR planning cycles.
• Salary bands: London, UK (Hybrid) – £94,059–£115,000 gross annually; UK remote (outside London) – £88,938–£109,000 gross annually.
• Work at one of the fastest‑growing tech startups, backed by top VC firms such as Balderton & EQT Ventures.
• A clear progression plan, with support to grow, lead, and own impact.
• Flexibility and support for work‑life balance.
• Company‑wide performance reviews every 4 months.
• Generous pay increases for high-performing team members.
• Equity top‑ups awarded across all levels in performance reviews.
• 25 days annual leave a year + public holidays (+ an additional day for every year you spend at Cleo, up to 30 days).
• 1 month paid sabbatical after 4 years at Cleo.
• 6 % employer‑matched pension in the UK.
• Private medical insurance via Vitality, dental cover, and life assurance.
• Online mental health support via Spill.
• Enhanced parental leave and workplace nursery scheme.
• Paid access to multiple AI platforms (ChatGPT, Codex, Claude) and the latest AI coding models.
• Choice between a Windows or an Apple computer.
• Regular socials and activities, online and in‑person, and many more.

We strongly encourage applications from people of colour, the LGBTQ+ community, people with disabilities, neurodivergent people, parents, carers, and people from lower socio‑economic backgrounds.