Senior Machine Learning Engineer, Risk Modeling

Block builds technology to increase access to the global economy. Across our ecosystem, including Square and Cash App, we create tools that help businesses run and grow, and individuals move, manage, and grow their money with confidence.
Square empowers sellers of all sizes with integrated, omnichannel tools to accept payments, manage operations, access financial services, and reach customers across online and in-person channels.
Cash App complements this by providing a fast, accessible financial platform for millions of people to send, spend, save, invest, and borrow, helping redefine how individuals interact with money.Operating at massive scale across both ecosystems means trust and safety are foundational. Our teams build systems that protect real people and businesses, safeguard financial activity, and ensure our products remain reliable, secure, and easy to use.
Block is a global, distributed company with a culture rooted in ownership, creativity, and impact. Whether supporting sellers on Square or customers on Cash App, we're united by a shared mission: to make the global economy more accessible and inclusive.
The Role
We're hiring Senior 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 on chargeback and fraud prevention as well as trust and safety initiatives supporting Cash App Families and teen banking.
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.
Team Focus Areas
Depending on your background and interests, you may join a team focused on one of the following areas:
Fraud & Chargeback Risk Build machine learning models and systems that detect fraudulent transactions, reduce chargebacks, and protect the integrity of payments across Cash App and Square.
Trust, Safety & Families Develop machine learning systems that enable safe and trustworthy financial experiences for teens and families by detecting risky or abusive behavior, strengthening account integrity, and supporting long-term trust in Cash App.
Both teams value first-principles thinking, rapid iteration, and shipping production ML solutions with real-world impact.
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

• 2+ 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

Block takes a market-based approach to pay, and pay may vary depending on your location. U.S. locations are categorized into one of four zones based on a cost of labor index for that geographic area. The successful candidate's starting pay will be determined based on job-related skills, experience, qualifications, work location, and market conditions. These ranges may be modified in the future.
To find a location's zone designation, please refer to this resource . If a location of interest is not listed, please speak with a recruiter for additional information.
Zone A:
$189,000 - $283,600 USD
Zone B:
$179,600 - $269,400 USD
Zone C:
$170,100 - $255,100 USD
Zone D:
$160,700 - $241,100 USD
Application Guidelines
Candidates may submit up to 9 active applications within a 60-day period. Reapplications to the same role are accepted 90 days after a previous application has been reviewed.
Use of AI in Our Hiring Process
We may use automated AI tools to evaluate job applications for efficiency and consistency. These tools comply with local regulations, including bias audits, and we handle all personal data in accordance with state and local privacy laws.
Contact us here with hiring practice or data usage questions.
Every benefit we offer is designed with one goal: empowering you to do the best work of your career while building the life you want. Remote work, medical insurance, flexible time off, retirement savings plans, and modern family planning are just some of our offering. Check out our other benefits at Block.
Block, Inc. (NYSE: XYZ) builds technology to increase access to the global economy. 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.