
Polar · Europe
WHY POLAR? It's never been easier to build, ship and scale software. But it's never been harder to monetize it. Modern startups look fundamentally different ...
It's never been easier to build, ship and scale software.
But it's never been harder to monetize it.
Modern startups look fundamentally different than prior generations:
Exceptional billing primitives, APIs and SDKs are essential, but delightful integration is not enough.
Startups need a billing platform designed for their speed of iteration. Combining billing and analytics in one platform to offer
customer- and feature unit economics in real-time. Offering built-in pricing and cost insights, simulations and optimizations
while simultaneously handling international compliance, tax management, fraud prevention and more.
That's Polar. We're building the next standard for applied AI startups.
Join our small, talented and engineering-led team across Europe as we build the infrastructure powering the next generation of
software companies.
We focus on shipping at high velocity to serve startup founders scale their businesses. Everything else is secondary.
We’re hiring a Senior Platform Engineer to architect and evolve the Polar platform - ensuring the system remains fast, resilient
and operationally sound as we scale.
Polar operates as a merchant of record, meaning our platform sits directly in the critical path of global payments, billing
infrastructure and financial workflows. Reliability, uptime and correctness are essential - while still maintaining the ability to
move quickly and ship product improvements.
You’ll work across the platform and infrastructure layers that power Polar - from core infrastructure and observability to
deployment safety, internal tooling and reliability engineering. In close partnership with the team, you’ll ensure the system
scales to handle increasing traffic, architectural complexity and regulatory demands without compromising stability, performance
or developer velocity.
This role is ideal for someone who treats reliability as a product requirement and scalability as an architectural discipline,
combining deep systems engineering experience with a passion for building reliable, scalable platforms and empowering engineering
teams through strong abstractions and automation.
While this role focuses primarily on the foundational layers of our platform, we value engineers who are comfortable moving across
the stack when needed to ship quickly and maintain momentum.
operational stability. Drive improvements in uptime, resilience and operational discipline as the system scales.
critical paths and design systems that scale with growing traffic and complexity.
incident response, reducing operational toil and making production behavior measurable and actionable.
needs to evolve. Improve infrastructure-as-code, environment management and operational safety mechanisms.
are safe, observable, reversible and fast to deploy.
debug and resolve issues in production.
stakeholders, to translate evolving regulatory requirements into clear technical abstractions while maintaining long-term
platform reliability and health.
Systems Thinking & Operating Mindset
distributed systems behave in production.
constraints as first-order design considerations.
functionality that powers the product. While this role focuses on platform layers, we value engineers willing to work across
the stack when needed.
integrity take precedence.
architecture and take shared responsibility for the long-term health of the system.
Technical Skills
cases.
reliability across large datasets.
how to prevent them in the future.
Experience
environment.
payouts and financial state management.
Nice-to-have: Open source contributions or side projects/apps to showcase.
mindset internally.
spend time.
Polar is a remote-first company, with team members across Europe, and our hiring process is fully remote via video calls and
email.
1. Application Review: We review your application and previous work.
2. Intro call: A short conversation with Birk (Founder and CEO) to learn more about you and give you a chance to learn more about
Polar.
3. Take-home Assignment: A practical exercise designed to reflect the kind of problems you would work on in the role.
4. Assignment Review: We review your assignment and feedback together
5. Team Conversations: 2-3 video calls where you get the chance to meet future team members.
6. Offer 🎉
7. Reference Calls
ABOUT THE ROLE We're looking for a senior engineer to help shape and lead the platform that other engineering teams build on top of. Our mission is to make AI agents and high-throughput backend systems easy for internal teams to adopt, and you'll own significant parts of how that platform is designed: the reusable libraries, Spring Boot starters, templates, and supporting tooling that the whole company depends on. You'll work across two worlds: * Agentic frameworks: the libraries, starters, and orchestration patterns that internal teams use to ship LLM-powered agents (Python/LangChain/LangGraph on the agent side, Kotlin/Spring Boot on the platform side), plus the supporting frameworks (evaluations, guardrails) that prove those agents actually work. * Core backend platform: Kotlin services and libraries and the shared building blocks other teams depend on. This is a high-leverage, builder-and-multiplier role. You'll make foundational design decisions, set the patterns and standards other engineers follow, and raise the bar for everyone building on the platform. Because the foundations you create sit underneath many teams' work, understanding how the company fits together, its products, domains, and the teams behind them is central to doing it well. While AI development experience is a great plus, we are looking for someone with genuine enthusiasm for the field, someone ready to dive deep into agentic systems and become our go-to expert. WHAT YOU'LL DO * Own the design of shared libraries, Spring Boot starters, and templates while making the architecture, API, and trade-off decisions that determine how easily internal teams ship on top of them. * Set the patterns and standards for our agentic frameworks, agent orchestration, tool use, memory, and the surrounding plumbing (message routing, human-in-the-loop workflows, MCP integration), and bring teams along with them. * Mentor and upskill product teams in Python-based AI agent development, including hands-on guidance with the LangChain and LangGraph frameworks. * Lead the evaluation and guardrail strategy so we can measure agent quality, reliability, and regressions. * Drive technical work across our Kotlin/Spring Boot platform and the client libraries that wrap it. * Build and maintain a clear map of the wider ecosystem (how our systems, domains, and teams connect) and use it to make foundational decisions that fit real needs across the company. * Drive adoption and multiply other engineers. Mentor teammates, review designs and code, run the docs/examples that turn a good framework into one that teams actually choose, and feed what you learn back into the platform. * Set the research direction in unfamiliar territory: identify where to invest, prototype the promising approaches, and turn the winners into production-ready foundations the rest of the org can rely on. * Raise the bar on developer experience, clear APIs, good defaults, useful errors, and documentation people actually read, and hold the platform to it. WHAT WE'RE LOOKING FOR * 7+ years of professional software engineering experience, including a track record of building libraries, frameworks, or platform components that other engineers built on. * Deep experience with Kotlin / the JVM and Spring Boot, and strong instincts for API and library design. You know what makes a foundation pleasant to build on versus painful. * Demonstrated technical leadership: you set direction, make and justify architectural trade-offs, and lift the engineers around you, with or without formal authority. * Genuine drive to lead on agentic AI and its surrounding tooling (frameworks, evaluation, guardrails, orchestration), and to become a go-to expert for the org. * The judgment to drive ambiguity to clarity: to take an open-ended or unfamiliar problem and turn it into a sound, well-scoped design others can execute. * A systems thinker who owns the bigger picture: you actively understand how the company's products, domains, and teams connect, and design for the whole, not just the module in front of you. * Excellent communication and a self-sufficient way of gathering context: you do your homework, ask sharp questions of the right people, and can explain and sell technical directions to both engineers and stakeholders. * Pragmatism about Python: Working knowledge of Python: You don’t need an extensive background in managing large-scale Python production environments, but you should be comfortable with the language. Since our tooling relies on Python/LangChain/LangGraph, we look for the ability to ramp up quickly and act as a senior lead across both our Kotlin and Python stacks NICE TO HAVE * Strong distributed systems background like messaging/queues (SQS, Redis), gRPC, event-driven architectures, including the failure modes and operational realities. * Cloud experience (AWS preferred) and infrastructure-as-code. * Experience growing a platform/DevEx practice by establishing standards, golden paths, and adoption across multiple teams. * Contributions to or maintenance of open-source libraries or frameworks. * Hands-on experience with LLMs, LangChain/LangGraph, or other agent frameworks. * Experience defining evaluation / experiment-tracking / observability strategy for ML or agent systems (e.g. Langfuse, MLflow, or similar).
WHY POLAR? It's never been easier to build, ship and scale software. But it's never been harder to monetize it. Modern startups look fundamentally different than prior generations: * Smaller teams * Exponential revenue growth relative to headcount * Higher variability in costs (LLMs) requiring more frequent pricing iterations * Laser focused on product development and distribution * Delegating and automating everything that is boilerplate – be it in their codebase or business operations. Exceptional billing primitives, APIs and SDKs are essential, but delightful integration is not enough. Startups need a billing platform designed for their speed of iteration. Combining billing and analytics in one platform to offer customer- and feature unit economics in real-time. Offering built-in pricing and cost insights, simulations and optimizations while simultaneously handling international compliance, tax management, fraud prevention and more. That's Polar. We're building the next standard for applied AI startups. Join our small, talented and engineering-led team across Europe as we build the infrastructure powering the next generation of software companies. We focus on shipping at high velocity to serve startup founders scale their businesses. Everything else is secondary. PRODUCT ENGINEERING AT POLAR Fullstack engineerings with a strong product sense and taste. As we grow, we'll gradually move towards more specialized roles between backend vs. frontend vs. product engineering. Therefore, we ask about your main strength in the application to ensure we maintain a strong & balanced team across the spectrum. OUR STACK * Frontend: React & Next.js with Tailwind CSS, Shadcn, TanStack Router and more. * Backend: Python (FastAPI), Postgres, Redis, Dramatiq. * Cloud: Vercel, Render & AWS. Always subject to change as we scale and new technologies emerge. ROLE & RESPONSIBILITIES We’re hiring exceptional Senior Product Engineers to join our growing remote-first team in Europe. You'll work across our entire stack to ship innovative features, enhancements and delights; obsessing over the developer experience and empowering them to scale their businesses. You're very comfortable jumping between frontend, backend, and infrastructure to autonomously identify, build, ship and scale features. We don't have a lot of meetings, red tape or code reviews. We celebrate and optimize our organisation for shipping high-quality software fast – each engineer deploys countless times a day. So you'll be given a lot of agency and autonomy to move fast towards our mission and serving our developer community. * Ship daily towards building the best monetization platform for developers in the world. * Design, build, and ship features, enhancements and delights end-to-end – jumping between frontend, backend, and infrastructure. * Collaborate with the team on architecture design, best practices, and ensuring high-quality code across our stack. * Continuously improve the quality of services and the overall developer experience. * Engage frequently with our developer community to identify pain points and solve them. WHAT WE'RE LOOKING FOR * 7+ years of experience building, shipping and scaling high-quality software. * You ship fast and can solve any problem thrown at you end-to-end. * Strong proficiency with our stack or a variety of similar programming languages and ability + desire to quickly learn and pickup new tools. * Strong problem-solving abilities with an eye for developer experience. * Experience with cloud infrastructure and multi-cloud environments. * Excellent collaboration skills - comfortable working closely with a small, high-performing team. It's a startup so we all have to lean-in across the board to. * You care deeply about your craft - be it delightful animations, thoughtful edge-case handling, developer experience or performance optimizations. * (Bonus) You're an ex-founder/startup CTO, open source maintainer or indie hacker. * (Bonus) Experience working with payments, billing, or developer tools. WHAT WE OFFER * Meaningful ownership: Small team & large surface area. You’ll directly influence how the company and platform scale. * Product-driven culture: We build to empower the next generation of software companies - and operate with the same builder mindset internally. * Competitive compensation: Salary and equity aligned with the impact of the role. * Exceptional team: Work with highly talented team members distributed across Europe. * Remote-first environment: Work from anywhere in Europe, with a home office setup budget available. * Annual team offsites: As the team is spread across Europe, we gather in person at least once a year to collaborate, plan, and spend time. * Health Benefits: Comprehensive health coverage to support you and your family. * Parental leave: Paid parental leave aligned with the standards and regulations of your local jurisdiction. HOW WE HIRE Polar is a remote-first company, with team members across Europe, and our hiring process is fully remote via video calls and email. HIRING PROCESS 1. Application Review: We review your application and previous work. 2. Intro call: A short conversation with Birk (Founder and CEO) to learn more about you and give you a chance to learn more about Polar. 3. Take-home Assignment: A practical exercise designed to reflect the kind of problems you would work on in the role. 4. Assignment Review: We review your assignment and feedback together 5. Team Conversations: 2-3 video calls where you get the chance to meet future team members. 6. Offer 🎉 7. Reference Calls
**This is a remote position open to candidates in Europe. For those based in the Czech Republic, a hybrid work model is also available. ABOUT US We are a leading product development partner specializing in custom web and mobile application development. With Silicon Valley founders and top-tier European tech talent, we operate from Prague and have successfully delivered over 65 software products for early-stage startups, scaleups, and global enterprises. * Founded in 2016 * Headquartered in Prague * Built and launched 65+ products * 90+ team members * Driving product innovation for leading US companies At OAK’S LAB, we take an AI-first approach, utilizing AI on almost every project. From streamlining design and testing workflows to enhancing developer productivity, our teams leverage tools such as Figma MCP Server, Playwright MCP Server, and Cursor, and we’re actively experimenting with remote AI agents to push the boundaries of what’s possible in product development. OUR PROJECTS Here are a few from our portfolio: * Nasdaq Private Market (Series C, Finance)- nasdaqprivatemarket.com * Blackpoint Cyber (Series B, Cybersecurity) - blackpointcyber.com * OpenLoop (Series A, Healthcare) - openloophealth.com THE ROLE Our product development team is looking for a Senior Fullstack Engineer who combines creative thinking, exceptional problem-solving skills, and technical expertise to build outstanding web and mobile applications for our clients. You’ll play a key part in building and scaling impactful digital products from the ground up. You’ll work as part of a dedicated product team alongside a Tech Lead, Product Manager, Designer, and a talented group of engineers, driving the success of innovative companies. Your role will involve everything from participating in high-level technical discussions to engineering and deploying complex features, giving you full ownership across the entire product development lifecycle. For ambitious engineers, we’ll provide the time, mentorship, and opportunities to step into a leadership role, where you can guide and mentor your own team over the longer term. You’ll also have the opportunity to join our internal AI Guild, a community where engineers share insights, experiment with cutting-edge AI tools, and learn from one another. RESPONSIBILITIES * Design, develop, and version high-quality web and mobile applications * Collaborate with product teams to understand feature requirements and translate them into technical solutions * Be accountable for an area of the application, its delivery, production-level quality, and its effective presentation to stakeholders * Understand the product and user needs to prioritize business value and functionality * Ensure the application meets all requirements of security and scalability * Write clean and scalable code * Engage in code reviews, provide constructive feedback, mentoring less senior engineers SKILLS & REQUIREMENTS * 5+ years of experience in building web solutions using Node and React * Experienced with Javascript/Typescript * Focus on code quality * Desire to learn new technologies and apply AI in your workflow * Strong analytical and problem-solving skills * Proactiveness and the capability to make a difference * Driven, hard work ethic, showing commitment * Ability to work effectively in a team environment, following Agile methodologies * Proficient in English * Experience with Python is beneficial but not essential OUR TECH STACK * Typescript * Node.js * React + Next.js * React Native * GraphQL, tRPC * Material UI * Playwright * PostgreSQL * Google Cloud Platform * Python * HuggingFace API, LLM APIs (eg OpenAI API), Langchain, Vector Databases for RAG Important Notice: OAK'S LAB communication, including interview requests and job offers, are only sent from an "@oakslab.com" or "@oaks-lab.com" email addresses (e.g., john@oakslab.com or john@oaks-lab.com). Any message from a different email domain is not associated with OAK'S LAB. We will never ask for payment information or banking details via email, phone, or any other communication channel during the interview process. If you receive messages using our name, domain, or brand assets in an attempt to impersonate us or act on our behalf, do not engage. Instead, report it to Econsumer.gov at Government Shutdown Notice / Aviso de cierre del gobierno (if you are in the EU), Federal Trade Commission (FTC) at Government Shutdown Notice / Aviso de cierre del gobierno , or the Securities and Exchange Commission (SEC) in case of investment fraud at SEC.gov | Report Suspected Securities Fraud or Wrongdoing (if you are in the US).