Staff Software Engineer, Square Cards

Since we opened our doors in 2009 the world of commerce has evolved immensely and so has Square. After enabling anyone to take payments and never miss a sale we saw sellers stymied by disparate outmoded products and tools that wouldnt work together.

So we expanded into software and started building integrated omnichannel solutions to help sellers sell online manage inventory offer buy now pay later functionality book appointments engage loyal buyers and hire and pay staff. Across it all weve embedded financial services tools at the point of sale so merchants can access a business loan and manage their cash flow in one place. Afterpay furthers our goal to provide omnichannel tools that unlock meaningful value and growth enabling sellers to capture the next generation shopper increase order sizes and compete at a larger scale.

Today we are a partner to sellers of all sizes large enterprise-scale businesses with complex operations sellers just starting as well as merchants who began selling with Square and have grown larger over time. As our sellers grow so do our solutions. There is a massive opportunity in front of us. Were building a significant meaningful and lasting business and we are helping sellers worldwide do the same.

The Role

Square helps business owners access manage and grow their money. The Square Debit Card is at the center of that experience a business card sellers use every day to pay vendors manage cash flow and reinvest in their business. The Cards team owns the entire cardholder journey from activation and digital wallet integration to spend incentives and rewards. Were building systems that help sellers trust Square with more of their financial lives.

Were looking for a Staff Product Engineer to shape the next generation of our card experience. Youll lead technical strategy for how we personalize and optimize key seller moments using data experimentation and ML to help sellers get value from Square faster and keep them engaged longer. This is a hands-on cross-functional role: youll work closely with PMs data scientists and ML engineers to build measure and iterate on new product hypotheses at scale.

What youll do

• Lead design and development of systems that drive seller engagement through incentives onboarding and spend experiences.
• Build and scale experimentation frameworks for testing offers activation flows and cardholder behaviors across millions of users.
• Partner with ML teams to integrate models that predict engagement and personalize incentives rewards or educational nudges.
• Develop infrastructure and pipelines that enable fast iteration and statistically sound decision-making.
• Collaborate with design product and analytics to translate insights into production features that improve retention and satisfaction.
• Mentor engineers across teams raising the bar for experimentation quality observability and data-driven development.
• Set technical direction for how the Cards team measures learns and ships product changes efficiently and responsibly.

You have

• 12 years of engineering experience including deep work in product-facing or ML-enabled systems.
• A strong background in backend or full-stack development using languages like Java Kotlin Ruby Go or Python.
• Experience building large-scale experimentation or personalization systems (A/B testing feature flagging model integration).
• Familiarity with modern ML workflows e.g. training/inference pipelines feature stores or real-time scoring and how to integrate them safely into production systems.
• A track record of influencing product direction through data and experimentation not just intuition.
• Strong collaboration and communication skills; able to bridge engineering product and data to ship measurable impact.
• Comfort working in tier 0 critical environments where accuracy and trust matter.

Technologies we use

• Backend: Java Kotlin Go Ruby on Rails
• Data & ML: Python Airflow Spark Snowflake TensorFlow Databricks
• Infra: Kubernetes AWS Terraform Protocol Buffers Temporal

Were working to build a more inclusive economy where our customers have equal access to opportunity and we strive to live by these same values in building our workplace. Block is an equal opportunity employer evaluating all employees and job applicants without regard to identity or any legally protected class. We will consider qualified applicants with arrest or conviction records for employment in accordance with state and local laws and fair chance ordinances. We believe in being fair and are committed to an inclusive interview experience including providing reasonable accommodations to disabled applicants throughout the recruitment process. We encourage applicants to share any needed accommodations with their recruiter who will treat these requests as confidentially as possible. Want to learn more about what were doing to build a workplace that is fair and square Check out our ID page.

Required Experience:

Staff IC