Senior Software Engineer – Backend (AI)

Personio's intelligent HR platform helps small and medium-sized organizations unlock the power of people by making complicated, time-consuming tasks simple and efficient. Our team of 1,500 Personios is building user-friendly products that delight our 16,000+ customers and their 1.5 million employees.

About The Role

We're hiring multiple Senior Backend Engineers into our AI team in London. This team owns Personio's AI experiences end to end. That means the model layer (how we interact with Bedrock, prompt tuning, RAG), the platform underneath it (infrastructure, data flow, the APIs our LLMs are exposed through), and the customer-facing side (how users actually trigger and interact with these features). Alongside the Personio Assistant, this team owns the agentic architecture that Personio's next generation of AI features will be built on. That includes the Analytics Agent launching this year, agentic experiences in Recruiting, and AI features embedded across Performance & Development and People Analytics, such as follow-up questions inside summaries and smart metrics on the analytics dashboard. You do not need a machine learning background. Most of this work is building well-designed, reliable backend systems, and it is not fundamentally different from building any other API. What is different is who you build it with and what sits on top: you will work day to day alongside machine learning engineers, and the systems you build are what every agentic experience at Personio will run on. If you are a strong backend engineer who wants real exposure to applied AI without moving away from engineering, this is a good place to do it.

What You'll Do

• Design and build the backend services and APIs that power Personio's AI Assistant and agent experiences
• Build out the underlying platform that upcoming agentic products across Personio will be built on
• Own features end to end, from problem definition through to production
• Work directly with machine learning engineers on the systems around retrieval, prompting, and model interaction
• Make architectural decisions in a young, fast-moving domain where the patterns are still being set
• Collaborate with Product, Design, and the teams building AI features into their own product areas

What We're Looking For

• Strong experience as a backend engineer in production environments
• Solid skills in Kotlin, Java, or a similar JVM language, and comfort picking up a new stack
• Experience designing and scaling APIs and distributed systems where reliability and correctness matter
• Comfort building from scratch rather than extending established platforms and internal tooling
• Clear communication, particularly across engineering disciplines

Nice to Have

• Experience working alongside machine learning or data engineering teams
• Exposure to LLM-based systems, RAG, or agent architectures
• Experience with AWS, and with Bedrock or a comparable model platform
• Interest in AI-assisted development workflows

Locations & Working Model

This role is based in London. We follow a hybrid working model with 2 days per week in the office. This team is building deliberately in London, so we are looking for people who can be part of that in person.

Why Personio

At Personio, we're building the People Operating System for Europe. You'll be joining a high-growth, product-led company where engineering plays a central role in shaping the business. AI is one of the most visible parts of that, and this team sits at the centre of it.

What you can expect:

• Competitive salary and equity
• 28 days holiday, increasing with tenure
• Hybrid working model (2 days per week in the office)
• 20 Flex Days to work from anywhere in Europe
• A strong engineering culture focused on ownership and impact