Senior Software Engineer, Fraud

Join the Future of Commerce with Whatnot!

Whatnot is the largest livestream shopping platform in North America and Europe to buy, sell, and discover the things you love. Whether it's trading cards, fashion, electronics, or live plants, our sellers are building real businesses across hundreds of categories. We're building live commerce at a scale that's never been done in the West, and there's no playbook to copy. The people here are shaping how an entirely new industry develops.

As a remote co-located team, we're inspired by our values and anchored in hubs across the US, UK, Ireland, Poland, Germany, and Australia. We move fast, stay close to our users, and focus on the work that drives the most impact.

We're one of the fastest growing marketplaces and were recently named #1 Best Startup Employer in America by Forbes.

The Fraud Experience team builds intelligent, real‑time systems that safeguard Whatnot’s marketplace from malicious activity. We design, develop, and deploy end‑to‑end, ML‑driven systems that proactively identify and mitigate fraud — blending real‑time detection with transparent, user‑centered enforcement.

What You'll Do

• Lead the full architecture of fraud detection, prevention, and intervention systems — spanning 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.

People who do well at Whatnot tend to be comfortable figuring things out as they go, biased toward action, and genuinely curious about what they're building. They care more about outcomes than credit and stay close to the product and the people using it.

As our next Software Engineer in Fraud team, you should bring 4+ years of software development experience in high‑growth environments, along with a strong bias toward action and impact.

What You'll 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 — you think critically about 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 — you focus relentlessly on delivering value for users and simplify wherever possible, moving fast without sacrificing quality.

• You’re entrepreneurial and relentless — you prioritize effectively, tackle hard problems with curiosity, and go 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…