Senior Software Engineer, Back-end (Fraud)

Stack

Responsibilities

• ▹Own and deliver quarterly goals for your team, leading engineers through ambiguity to solve open-ended problems
• ▹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
• ▹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, vendor configuration) into a repeatable, low-friction path
• ▹Integrate region-specific fraud and risk vendors and help operationalize the ML and AI signals that power real-time decisioning, using modern AI tooling to move faster
• ▹Support peers and stakeholders across the product development lifecycle, collaborating with Product, Machine Learning, Analytics, and Fraud Strategy
• ▹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
• ▹Foster a culture of quality and ownership, setting and improving code review and design standards, mentoring teammates
• ▹On-call rotation is a requirement of this role

Requirements

• ▹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 (setting intent, critically evaluating generated code, owning correctness, quality, and security) 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

Nice to have

• ▹Experience with Snowflake, dbt, Airflow, or Chronosphere
• ▹Background in fraud prevention, risk systems, or real-time decisioning
• ▹Experience building for multiple markets or regions - internationalization or localization
• ▹Experience working in fintech or other highly regulated environments, with strong understanding of risk, compliance, and operational constraints

Soft skills

What we offer

• ▹Flexible Spending Wallets for tech, food, and lifestyle
• ▹Away Days - wellness days to take off work and recharge
• ▹Learning & Development programs
• ▹Parental benefits
• ▹Employee Resource & Community Groups
• ▹Health care coverage - full premium coverage for you and your dependents
• ▹Time off - competitive vacation and holiday schedules
• ▹ESPP - an employee stock purchase plan at a discount

About the company

Affirm is reinventing credit to make it more honest and friendly, giving consumers the flexibility to buy now and pay later without any hidden fees or compounding interest. The Fraud Engineering organization builds the foundational and tactical software that enables Affirm to respond strategically to fraud in real time and after the transaction, supporting business growth while protecting Affirm, its customers, and its merchants.