Backend Engineer (Rust, Kotlin)

Engineering at hyperexponential

At hyperexponential (hx) we are transforming the traditional insurance industry with our groundbreaking SaaS platform, hx Renew. Insurers use it to build complex mathematical models that enable smarter, faster pricing decisions—whether it’s calculating the cost to insure a global superstar’s concert tour or protecting entire states from natural disasters.

With hx Renew, insurers can rapidly develop and iterate pricing models in Python and React within a modern software environment, free from the burden of legacy tech. What once took months now takes weeks—or even days. This agility has made our product the go-to platform for insurers worldwide.

In just five years, our winning formula has earned the trust of industry giants like Aviva and Top 5 US insurers, as well as cutting-edge innovators like Convex and Inigo. Our engineering team—made up of some of the brightest (and kindest!) minds in the industry—pushes technological boundaries every day through creative innovation and regular hackathons.

Your Unique Mission

As a Backend Engineer in our Shared Architecture team (Sharc for short 🦈), you'll build the essential systems that power the entire engineering organisation. From SSO and identity, to our API gateway, to event-driven data platforms - you’ll shape the technical foundation that enables teams to build fast, integrate seamlessly, and scale with confidence.

This is not a backend role that sits in a corner. The tools you build will be used by every engineer, and the quality of your work will ripple through the entire product. If you thrive on solving deep technical puzzles and love helping others move faster by building robust infrastructure—this is your kind of challenge.

What You’ll Do

• Design and develop backend services in Rust and Kotlin

• Build core platform components like our API gateway, SSO, webhook infrastructure, and data mesh

• Improve reliability, observability, and security of internal APIs

• Collaborate with product teams to help them adopt and integrate shared tooling

• Lead and participate in architecture and design discussions

• Document clearly, and automate where it counts—especially around API validation and access controls

• Develop and maintain access control and authorisation systems (e.g. OAuth2, OIDC, SpiceDB)

What Makes This Role Exciting

• You’re building the backbone of a fast-growing product company

• Your work directly influences how quickly and safely every product team can ship

• You’ll work in a high-trust, collaborative team culture that values clarity, autonomy, and technical excellence

• You’ll tackle interesting challenges like balancing flexibility with standardisation, designing for scale without complexity, and enabling adoption without friction

• You’ll work on high-impact projects like:

  • A unified SSO system used across internal and external tools

  • A webhook platform that powers real-time integrations

  • API observability and validation tooling that’s actually delightful to use

What You Bring

Must-Haves:

• Solid experience as a backend engineer, ideally in platform or infrastructure teams

• Proficiency in Rust or Kotlin [or other JVM language] (and willingness to learn both)

• Experience working with AWS and infrastructure-as-code (Terraform preferred)

• Strong grasp of API design, authentication/authorisation, and secure system patterns

• A collaborative mindset and the ability to communicate technical ideas clearly

• A passion for clean, testable, well-documented code

Nice-to-Haves:

• Experience with identity systems like OAuth2, OIDC, or SSO

• Knowledge of API gateways, webhooks, SpiceDB, or event-driven architecture

• Exposure to developer platforms or data mesh systems

What Success Looks Like

30 Days: You’ve set up, contributed to early features, and understand the ecosystem and tools.

60 Days: You’re owning small projects and helping a product team adopt our tools.

90 Days: You’ve led a project to production, improved a core system, and started shaping our engineering standards.

Long-term: You’ve become a go-to engineer on shared infrastructure, helping shape the roadmap, mentoring others, and driving scale and reliability across the platform.

Why Other Engineers Joined Us

• Exceptional Growth: Profitable and rapidly scaling (2× ARR YoY). Backed by $73M Series B funding to support bold innovation

• Top-Tier Team & Culture: Collaborative, high-performing culture with 80+ engineers across London and Warsaw. Driven by ownership, curiosity, and kindness

• Meaningful Impact: Adopting cutting-edge solutions. Focus on solving real problems that revolutionise the field. Being challenged and testing ideas quickly.

What We Offer:

• Salary + Equity (stock options)

• £5,000 for individual and group training and conference budget

• Mental health and therapy provision via ⁠Spectrum.life

• Individual wellbeing allowance via Juno

• Access to Healthcare (Luxmed) and Gym (Multisport)

• Team breakfasts and lunches, snacks, drinks fridge, fun office @ Brain Embassy

• Huge opportunity for personal development and mastery as we grow together

• and more!

This role is Warsaw based (flexible hybrid, 2 days in the office). Learn more about our ways of working here: https://hx.wiki/wow

Interview Process

Initial chat with our Talent team to kick things off

• Manager Interview (60 minutes)

• Technical Assessment (120 minutes)

• Values Interview (60 minutes)

• We offer!