Software Engineer Kotlin & Rust

hyperexponential; Warszawa; Hybrid; PLN 180,000 - 240,000; Full time

Job summary

A cutting-edge technology firm in Warsaw seeks a Software Engineer to develop backend services and core platform components in Rust and Kotlin. This role is crucial for supporting the engineering organization, ensuring seamless integration and reliability. A collaborative environment with a focus on innovative solutions awaits you. The role offers competitive salary options under both UoP and B2B contracts.

Benefits

25 days of non-working leave + Polish bank holidays

£5,000 GBP budget for Learning & Development

Mental Health Support and Therapy

Private Healthcare Insurance

Top-spec work equipment

Monthly Wellbeing allowance

Qualifications

• Solid experience as a backend engineer, ideally in platform or infrastructure teams.
• Proficiency in Rust or Kotlin (and willingness to learn both).
• Strong grasp of API design, authentication/authorization, and secure system patterns.

Responsibilities

• Design and develop backend services in Rust and Kotlin.
• Build core platform components like our API gateway and SSO.
• Collaborate with product teams to help them adopt and integrate shared tooling.

Skills

Backend development experience

Proficiency in Rust

Proficiency in Kotlin

Experience with AWS

API design skills

Collaborative mindset

Tools

Terraform

Job description

Location and Salary

Location: Hybrid 2 days per week, based in Warsaw

Salary for Senior (IC3):

• UoP (Contract of Employment) = 18,000 - 25,000 PLN per month gross
• B2B = 20,000 - 29,000 PLN per month net +VAT

About hyperexponential (hx)

At hyperexponential, we’re building the AI-powered platform that enables the world’s most critical decisions in a $7 trillion industry, which risks to take, and how to price them. These are the decisions that shape real-world outcomes: whether rockets successfully launch into space, autonomous vehicles make it to market, or communities recover after major storms.

Until now, insurers have been making billion-dollar decisions using outdated tools. We’re changing that. Our platform brings together data, AI, and human expertise to give insurers the fastest path from submission to decision - helping them move faster, act smarter, and take on more risk with confidence.

Backed by a16z, Highland Europe, and Battery Ventures, we’re scaling globally - already trusted by nearly 50 of the world’s largest insurers, with zero churn and billions in premiums flowing through hx.

What began as a single product in one market has rapidly evolved into a multi-product, multi-territory platform powering every stage of pricing and underwriting. AI is at the core of what we do - from building the world’s first domain-specific AI peer programmer for insurance (think GitHub Copilot with a PhD in actuarial science) to shaping agentic workflows that reinvent how this industry operates.

What makes hx different is the people who build it. Here, impact isn’t tied to title or tenure; it’s defined by the challenges you take on and the discipline you bring. Surrounded by peers who stretch you, you’ll do the best, hardest work of your life in a company engineered to endure.

If that sounds like you, join us in building what comes next.

Your Unique Mission

As a Software 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.

Interview Process

1. Initial screening with Talent team to kick things off (30 minutes)

2. Manager Interview (60 minutes)

3. Technical Assessment (120 minutes)

4. Values Interview (60 minutes)

5. We offer!

How hx Warsaw Works

At hyperexponential, we believe in a balance between remote work, and building relationships across teams and locations. You’ll have your main office in Warsaw, 2 days per week, with also ability to travel to London HQ to meet the wider team. International travel will be much less frequent, perhaps 2-3 times a year.

Warsaw HQ was established in 2023, quickly hiring our first handful of high-calibre engineers. Fast-forward to today in 2025, there are 50+ in Warsaw and surrounding cities who travel for the collaborative environment.

On Wednesdays you’ll often find Warsaw HQ organising team lunch paid by hx, getting drinks after hours. The office is also dog-friendly, so feel free to bring yours along!

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 Your Offer Could Look Like

B2B

• Share Options at a highly successful Series B company
• 25 days of non-working + Polish bank holidays
• £5,000 GBP budget for Learning & Development
• Mental Health Support and Therapy via Spectrum Life
• Optional for you: access to Private Healthcare via Luxmed + Multisport (fully funded by yourself as B2B Contractor)
• Top-spec laptop (MacOS or Windows)

Contract of Employment (UoP)

• Share Options at a highly successful Series B company
• £5,000 GBP budget for Learning & Development
• 26 days of holiday + Polish bank holidays
• Company pension
• Company Sick Pay for 10 days at 100% salary
• Mental Health Support and Therapy via Spectrum Life
• Monthly Wellbeing allowance via Juno
• Private Healthcare Insurance via Luxmed
• Multisport - Classic level
• Top-spec work equipment (MacOS, Windows + additional monitors, mechanical keyboards etc)