Senior Software Engineer, Back-end (Fraud)

About Affirm

At Affirm, we exist for the moments that matter—giving people a clear, predictable way to pay over time, with no hidden fees, no surprises, and no tradeoffs on what matters most.

Role Overview

The Fraud Engineering organization builds the foundational and tactical software that enables Affirm to respond strategically to fraud - both in real time and after the transaction. Our mission is to support business growth while protecting Affirm, our buyers, and our merchants. We evaluate risk at critical decision points in the user journey, rapidly adapt to evolving fraud patterns, and equip operations teams with the tools needed to investigate and mitigate fraud at scale.

The Fraud International Team (FIT) leads the engineering effort to extend Affirm's Fraud Decisioning System into markets beyond the US - Canada, the UK, Australia, and growing rapidly. We own real-time fraud decisioning for these markets, integrate region-specific risk vendors, and are building the platform that lets Affirm stand up fraud protection in a new country quickly and safely.

We’re looking for a Senior Software Engineer to join our fully remote team based in Europe. You’ll collaborate closely with stakeholders across North America - including teams in Product, Compliance, Machine Learning, Fraud Operations, Fraud Strategy, and other Fraud Engineering teams.

What You'll Do

• You will own and deliver quarterly goals for your team, leading engineers through ambiguity to solve open-ended problems, and ensuring that everyone is supported throughout delivery.
• You will design and implement real-time fraud decisioning services and APIs in Python or Kotlin, extending Affirm's Fraud Decisioning System to markets beyond the US.
• You will build and evolve the platform and tooling that let Affirm launch fraud decisioning in a new country quickly—turning market-by-market setup (rules, models, and vendor configuration) into a repeatable, low-friction path so launches scale sub-linearly with the number of markets.
• You will integrate region-specific fraud and risk vendors and help operationalize the machine learning and AI signals that power real-time decisioning, while using modern AI tooling to move faster as an engineer.
• You will support peers and stakeholders across the product development lifecycle - collaborating with Product, Machine Learning, Analytics, and Fraud Strategy, articulating technical constraints, and partnering on decisions that properly weigh risks and trade-offs.
• You will support the operations and availability of your team's systems by creating and monitoring metrics, escalating when needed, and contributing to keep-the-lights-on and on-call efforts.
• You will foster a culture of quality and ownership - setting and improving code review and design standards, mentoring teammates, and leading by example.

Total Rewards

We believe the people building honest financial products at Affirm should share in its success. That's why our total rewards are designed to support your health, growth, financial well-being, and future. In service of our mission, we reward employees through a combination of base pay, equity (from parent company), and comprehensive benefits.

• Base Pay: POL base pay range per year: 308,000 zł - 428,000 zł.
• Equity: All employees in this role are eligible to receive equity from the parent company each year. New hire equity: $32,000-$48,000; Annual Refresh: $10,000; Reward equity: $0-$150,000.
• Stipends: Flexible spending wallets for technology and wellbeing related needs, reimbursable up to 1390 zł per month.
• Time Off: Competitive paid time off, paid public holidays, and additional paid Away Days.
• Healthcare: Comprehensive private healthcare through Lux Med's Platinum package. We cover 100% of premiums for employees and their dependents.
• Well-being: A MultiSport card to support your health and well-being. Mental well-being support through Lyra, including up to 12 confidential counseling or coaching sessions each year.
• Financial Support: Financial well-being support through Northstar, with unlimited access to Certified Financial Advisors and planning tools at no cost. Employee stock purchase plan (ESPP) lets you buy Affirm stock at a discount.
• Growth: Learning and development programs to help you grow professionally.
• Family Support: Family healthcare support through Maven and parental leave support through Parentaly.
• Culture: Employee Resource Groups (ERGs) that foster connection and inclusion. Remote-first work environment.

What We Look For

• 5+ years of experience building backend systems at scale using Python or Kotlin.
• Experience with distributed systems and infrastructure using AWS, MySQL/PostgreSQL, and Kubernetes.
• Strong system design skills and a track record of delivering maintainable, extensible services.
• Fluency with AI-driven engineering - every Affirm engineer builds with tools like Claude Code and most PRs are co-authored with AI, so directing and orchestrating AI and excelling in the reviewer's seat is a core expectation.
• Proficiency in SQL and working with data-rich environments.
• Familiarity with CI/CD practices and safe production deployments.
• Strong written and verbal communication skills, especially in distributed teams.
• A proactive, ownership-driven mindset with a focus on learning and team success.
• Experience with Snowflake, dbt, Airflow, or Chronosphere (nice to have).
• Background in fraud prevention, risk systems, or real-time decisioning (nice to have).
• Experience building for multiple markets or regions - internationalization or localization (nice to have).
• Experience working in the fintech sector or other highly regulated environments, with a strong understanding of risk, compliance, and operational constraints (nice to have).