Senior Machine Learning Engineer, Risk Modeling

Location: Bay Area, CA, United States of America

Department: 11003 Risk - Prod Dev - Square

Block builds simple, powerful tools that make progress towards an economy that’s truly open to all. Each of our brands unlocks different aspects of the economy for more people. Square makes commerce and financial services accessible to sellers. Cash App is the easy way to spend, send, and store money. Afterpay is transforming the way customers manage their spending over time. TIDAL is a music platform that empowers artists to thrive as entrepreneurs. Bitkey is a simple self-custody wallet built for bitcoin. Proto is a suite of bitcoin mining products and services. Together, we’re helping build a financial system that is open to everyone. Join us.

The Role

We’re hiring Senior and Staff Machine Learning Engineers to join Block’s Risk Machine Learning organization, where teams apply ML at massive scale to detect, prevent, and reduce fraud and abuse across Cash App and Square.

This opening supports multiple senior-level roles, with team placement determined through a collaborative matching process based on your experience, interests, and current business needs. Today, we’re growing teams focused fraud & abuse prevention, merchant risk, credit underwriting (consumer & commercial lending), buy-now-pay-later decisioning, AI-powered customer support & conversational AI, agentic automation for investigations, and model risk governance. We'd love to hear from you whether your background is in adversarial ML, NLP/LLMs, credit modeling, or model validation.

Across teams, your work will directly protect our ecosystem, reduce financial loss, and enable safe, seamless financial experiences for millions of customers, sellers, and families.

You Will

• Partner with product, engineering, data science, policy, and operations to design and productionize ML-driven risk solutions at scale
• Own end-to-end machine learning systems — from problem definition and modeling to deployment, monitoring, and iteration
• Lead technical decision-making within your workstreams and influence ML strategy and planning
• Build tooling and processes that improve the speed, reliability, and impact of the ML development lifecycle
• Apply state-of-the-art modeling techniques and third-party data sources to improve detection and decision-making
• Investigate emerging fraud, abuse, and risk patterns to proactively inform product safeguards and policy
• Collaborate closely with ML platform and engineering teams to ensure models operate reliably in real time and at scale

You Have

• 8+ years of industry experience in machine learning, applied AI, or related fields
• Bachelor’s degree in a quantitative field (Computer Science, Engineering, Statistics, Physics, Applied Math); Master’s or PhD preferred
• Proven experience independently designing, deploying, and maintaining ML solutions in production
• Strong familiarity with techniques such as tree-based models, deep learning, transfer learning, or reinforcement learning
• Experience influencing technical direction and collaborating with cross-functional partners at scale
• Strong communication skills, sound judgment, and an ownership mindset
• Curiosity and alignment with Block’s mission of economic empowerment

Technologies We Use and Teach

• Python (NumPy, Pandas, scikit-learn, XGBoost, PyTorch, TensorFlow/Keras)
• PySpark, MLflow, workflow orchestration tools (Airflow, Prefect)
• GCP (Vertex AI), AWS
• Snowflake, MySQL, Tableau, Mode
• Containerization, CI/CD, and production ML best practices