Mid-Senior Backend Engineer

Summary

Join Cleo, a fast-growing fintech unicorn, and become a Backend Engineer contributing to the core product's decisioning systems. You will integrate ML-driven credit and eligibility models into a Ruby on Rails monolith, focusing on productionizing services from data ingestion to monitoring. Collaborate with ML engineers, analysts, and PMs to ensure smooth model output and stakeholder understanding. Improve the Ruby monolith for users and engineers. This role requires expertise in Ruby, experience with ML model integration, and a focus on system reliability. Cleo offers a competitive compensation package, flexible work arrangements, and various benefits.

Requirements

• You’re a backend engineer who’s comfortable working in technically complex domains - particularly those involving machine learning, financial decisioning, or large-scale data systems
• You're proficient in Ruby and have experience building and maintaining production systems that interface with machine learning models, data pipelines, or high-throughput decision engines
• You care about observability, system reliability, and deployment best practices
• You know how to make integrations robust and maintainable, and how to ensure they operate correctly in production over time
• You’re data-aware - able to reason about data lifecycle, ownership, transformations, and how downstream consumers rely on it
• You’re also a strong cross-functional collaborator, able to work closely with product managers, analysts and ML engineers to debug issues and iterate quickly

Responsibilities

• Integrate ML-driven credit and eligibility models into our Ruby on Rails monolith
• Own the productionisation of those services: from data ingestion and interface design to monitoring, alerting, and runtime observability
• Work closely with ML engineers, analysts, and PMs to expose model outputs cleanly, help debug behavioral anomalies, and ensure that stakeholders have the tooling they need to understand how decisions are made
• Be part of our wider Ruby chapter, working across our Ruby monolith to improve it for both our users as well as your fellow engineers

Preferred Qualifications

Exposure to Python and ML concepts is a plus, but deep ML knowledge isn’t required

Benefits

• A competitive compensation package (base + equity) with bi-annual reviews, aligned to our quarterly OKR planning cycles
• Work at one of the fastest-growing tech startups, backed by top VC firms, Balderton & EQT Ventures
• A clear progression plan
• Flexibility
• Work where you work best
• Company-wide performance reviews every 6 months
• Generous pay increases for high-performing team members
• Equity top-ups for team members getting promoted
• 25 days annual leave a year + public holidays (+ an additional day for every year you spend at Cleo, up to 30 days)
• 6% employer-matched pension in the UK
• Private Medical Insurance via Vitality, dental cover, and life assurance
• Enhanced parental leave
• 1 month paid sabbatical after 4 years at Cleo
• Regular socials and activities, online and in-person
• We'll pay for your OpenAI subscription
• Online mental health support via Spill
• Workplace Nursery Scheme