Software Engineer, Fraud

About Whatnot

Whatnot is the largest live shopping platform in North America and Europe, enabling users to buy, sell, and discover beloved items. We are redefining e-commerce by seamlessly blending community, shopping, and entertainment. As a remote co-located team, we are driven by innovation and anchored in our core values, with hubs across the US, UK, Germany, Ireland, Poland, and Australia. We are actively building the future of online marketplaces, together.

Our live auctions offer a diverse range of items, from fashion, beauty, and electronics to collectibles like trading cards, comic books, and even live plants. We are a fast-growing marketplace seeking bold, forward-thinking problem solvers across all functional areas. Explore the latest Whatnot updates on our news and engineering blogs, and join us in empowering individuals to turn their passions into businesses and connect people through commerce.

The Role of a Software Engineer, Fraud

The Fraud Experience team at Whatnot is dedicated to building intelligent, real-time systems that protect our marketplace from malicious activity. As a Software Engineer, Fraud, you will design, develop, and deploy end-to-end, ML-driven systems that proactively identify and mitigate fraud, ensuring a secure and transparent experience for all users.

What You'll Do

• Lead the full architecture of fraud detection, prevention, and intervention systems, encompassing machine learning, backend, and client-side components.
• Build intelligent user graphs to model behavioral patterns, detect collusion networks, and uncover account connectivity at scale.
• Design, train, and deploy both traditional ML and LLM-powered models to detect fraudulent activity across users, payments, and marketplace interactions.
• Develop scalable data pipelines and real-time inference systems capable of supporting high-volume, low-latency ML workloads.
• Create human-in-the-loop systems that continuously refine detection accuracy and adapt to evolving adversarial tactics.
• Perform deep behavioral and adversarial data analysis to surface emerging fraud trends and drive continuous system improvement.
• Stay ahead of the curve by translating new insights into adaptive, production-ready systems that evolve as fast as our adversaries.

We offer flexibility to work from home or from one of our global office hubs, and we value in-person time for planning, problem-solving, and connection. Team members in this role must live within commuting distance of our Los Angeles, New York, San Francisco or Seattle hub.

What You'll Bring

We look for individuals who embody a low ego, growth mindset, and high-impact drive. As our next Software Engineer, Fraud, you should bring:

• Bachelor’s degree in Computer Science, Statistics, Applied Mathematics, Economics, or a related technical field.
• 4+ years of software engineering experience building systems for consumer-scale traffic and reliability.
• 1+ years writing production-grade Python code and working with ML libraries (e.g. PyTorch, LightGBM).
• 1+ years of experience in machine learning or fraud prevention domains.
• Deep business intuition and a data-driven mindset, critically considering how abuse prevention systems affect growth and user experience.
• Fluency with data tooling, including data warehouses (e.g. Snowflake) and transformation frameworks (e.g. dbt, Dagster).
• Strong communication skills and the ability to lead initiatives across product areas, collaborating closely with leadership, data science, and product teams.
• Experience working in a remote-first environment and producing well-tested, reproducible work.

What Sets You Apart

• You’re impact-obsessed, relentlessly focusing on delivering value for users and simplifying wherever possible, moving fast without sacrificing quality.
• You’re entrepreneurial and relentless, prioritizing effectively, tackling hard problems with curiosity, and going above and beyond to make things happen.
• You have a growth mindset and love digging into ambiguous user problems, crafting data-driven solutions, and shipping improvements quickly.
• Hands-on machine learning or data science experience in production environments.

Benefits at Whatnot

Whatnot offers a comprehensive benefits package, including:

• Generous Holiday and Time off Policy
• Health Insurance options including Medical, Dental, Vision
• Work From Home Support and Home office setup allowance
• Monthly allowance for cell phone and internet
• Care benefits and a Monthly allowance for wellness
• Annual allowance towards Childcare
• Lifetime benefit for family planning, such as adoption or fertility expenses
• Retirement; 401k offering for Traditional and Roth accounts in the US (employer match up to 4% of base salary) and Pension plans internationally
• Monthly allowance to 'dogfood' the app (all Whatnauts are expected to develop a deep understanding of our product by using Whatnot as both a buyer and a seller).
• Parental Leave: 16 weeks of paid parental leave + one month gradual return to work (company leave allowances run concurrently with country leave requirements which take precedence).

Key skills/competency

• Fraud Detection
• Machine Learning
• Real-time Systems
• Data Engineering
• System Architecture
• Python Programming
• Data Analysis
• Risk Mitigation
• Distributed Systems
• LLM Integration