Staff Machine Learning Engineer, Ads at Whatnot

Whatnot; Kraków; On-site; PLN 911,000 - 1,116,000; Full time

Benefits offered by this job

Holiday and time off

Health Insurance

Work from home support

Home office setup

Internet allowance

Childcare support

Retirement plans

Parental leave

Job summary

Whatnot in Kraków is hiring a Staff Machine Learning Engineer, Ads to shape the engineering foundation of our advertising marketplace on site in Kraków. You will design high-throughput, low-latency backend systems powering ad auctions, bidding, pacing, ranking, and delivery, collaborating with product, ML, and infra teams.

You will own architecture decisions, lead end-to-end features, and mentor engineers while delivering scalable solutions for a global marketplace.

Qualifications

• Bachelor’s degree or equivalent experience; 8+ yrs Staff or 10+ yrs Senior Staff in backend/distributed systems.
• Strong fundamentals in consensus, partitioning, replication, coordination and sharding.
• Deep experience with high-throughput, low-latency services and stream processing.
• Proficient in Python or Go and scripting.
• Experience with messaging, caches, time-series stores, and data pipelines.
• Proven architecture leadership for ads/ranking/ML serving contexts.

Responsibilities

• Architect and lead high-throughput backend systems powering ad auctions and ranking.
• Design mechanisms balancing seller value, buyer experience, and marketplace efficiency.
• Develop services for budget management, forecasting, and measurement.
• Integrate real-time auction services with ML models and data pipelines.
• Own performance, resilience, and observability of critical services.
• Drive architectural decisions and capacity planning across teams.
• Lead technical reviews, mentor engineers, and raise engineering bar.
• Collaborate with product, ML, and infra teams to ship fast with quality.

Skills

Distributed systems

Low latency

Backend design

Python

Go

Messaging

Data pipelines

Communication

Leadership

Education

BSc in CS or related field

Tools

Kafka

Flink

Redis

RocksDB

Job description

Apply for Staff Machine Learning Engineer, Ads at Whatnot in Kraków, ML, PL. This Full time on site position offers great opportunities for career growth.

Join the Future of Commerce with Whatnot! Whatnot is the largest live 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 the #1 Best Startup Employer in America by Forbes. Check out the latest Whatnot updates on our news and engineering blogs and join us as we enable anyone to turn their passion into a business and bring people together through commerce.

Role Ads is a growing engineering team dedicated to building the systems that help Whatnot sellers grow their businesses. Our products operate at the intersection of marketplace dynamics, auction mechanics, ranking, and distributed systems. As an engineer on the Ads team, you will shape the technical foundation of Whatnot’s advertising marketplace. You’ll design auction systems that allocate limited buyer attention across sellers, balance marketplace and customer outcomes, and operate reliably at Whatnot’s scale. This includes bidding, pricing, pacing, ranking, forecasting, and real-time decision-making. This role requires strong technical judgment, comfort navigating ambiguous domains, and the autonomy to lead foundational projects from inception through production. You’ll work closely with product, machine learning, and infrastructure teams to make sound trade-offs and ship high-impact systems quickly without compromising quality.

In this role, you will…

• Architect and lead the implementation of high-throughput, low-latency backend systems that power ad auctions, bidding, pacing, ranking, and delivery.
• Design auction mechanisms that balance seller value, buyer experience, marketplace efficiency, and long-term ecosystem health.
• Build foundational services for budget management, allocation, forecasting, experimentation, attribution, and measurement.
• Develop reliable integrations between real-time auction services, machine learning models, data pipelines, and marketplace systems.
• Own the performance, resilience, observability, and scalability of critical services throughout their production lifecycle.
• Define service contracts, architectural patterns, fault-isolation strategies, and capacity plans for systems used by multiple product teams.
• Lead technical decisions for new auction and monetization capabilities, including how experiments graduate into durable platform infrastructure.
• Partner with product and machine learning teams to translate marketplace problems into practical backend and algorithmic solutions.
• Lead design and code reviews, mentor senior engineers, and raise the engineering bar across system design, testing, deployment, and operations.
• Participate in incident response, root-cause analysis, and postmortems for critical production systems.
• Develop the technical roadmap for auction infrastructure and connect foundational investments to measurable seller, buyer, and marketplace outcomes.

You Curious about who thrives at Whatnot? We’ve found that embodying a low ego, growth mindset, and high-impact drive goes a long way here.

As our next Staff Software Engineer you should have:

• Bachelor’s degree in Computer Science, a related field, or equivalent work experience 8+ years (for Staff) or 10+ years (for Senior Staff) of backend/distributed systems engineering experience.
• Strong mastery of distributed systems fundamentals: consensus, partitioning, replication, coordination, sharding, state management, etc.
• Deep experience with high-throughput, low-latency services and stream processing (e.g., Kafka, Flink, etc.).
• Strong software design, algorithmic, and data-structure skills.
• Proficiency in one or more languages (e.g., Python, Go) and scripting.
• Experience with messaging, caches (e.g., Redis, RocksDB), time-series stores, and data pipelines.
• Proven track record of leading architecture and scaling core systems under high load, especially in an ads, ranking, or ML serving context.
• Excellent communication skills, ability to influence cross-organizational stakeholders.
• Proven track record of delivering features end-to-end and can ship products and features lightning-fast without sacrificing quality.
• Strong ownership instincts — capable of driving projects from inception to production and beyond.
• The ability to pick up on new technologies very quickly.
• Startup experience at a high-growth company — working in fast-paced, rapidly evolving product environments with frequent experimentation (nice to have).
• Experience with ads systems (bidding, auction, attribution, measurement, etc.), infrastructure, and international commerce (nice to have).

Compensation

The salary range may be inclusive of several levels that would be applicable to the position. Final salary will be based on a number of factors including, level, relevant prior experience, skills, and expertise. This range is only inclusive of base salary, not benefits (more details below) or equity. Compensation Range: $245K - $300K

Benefits

• Generous Holiday and Time off Policy
• Health Insurance options including Medical, Dental, Vision
• Work From Home Support
• Home office setup allowance
• Monthly allowance for cell phone and internet
• Care benefits
• 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
• 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.

EOE Whatnot is proud to be an Equal Opportunity Employer. We value diversity, and we do not discriminate on the basis of race, religion, color, national origin, gender, sexual orientation, age, marital status, veteran status, parental status, disability status, or any other status protected by local law. We believe that our work is better and our company culture is improved when we encourage, support, and respect the different skills and experiences represented within our workforce.