Senior Software Engineer

Senior Software Engineer

Design and build the next-generation Decision Management Platform: the real-time system that scores and approves billions of payment transactions. The role is hands‑on – write code, run prototypes, and use AI coding tools to ship faster and at higher quality. Work directly with senior engineers, architects, and product managers to deliver features that make the platform faster, more reliable, and cheaper to run.

• Write production code for services, tooling, and platform features.
• Design and implement components of large distributed systems.
• Build reusable services, libraries, and integrations.
• Take prototypes from idea to working software.
• Pick the right frameworks, libraries, and tools by weighing quality, cost, latency, and reliability.
• Make clear trade‑offs in the systems you own and explain them to your team.
• Use AI coding tools as your default way of working and share patterns, demos, and tips with your team.
• Automate the boring parts of development.
• Improve what you own by making the customer experience better, simplifying designs to cut cost or latency, and paying down technical debt, fixing resiliency gaps, and closing operational risks.
• Contribute to designs that span multiple services and give useful feedback in design and code reviews.
• Mentor peers and junior engineers, interview candidates, and help raise the hiring bar.

• Track record of delivering real features in real distributed systems at scale.
• Hands‑on experience with high‑throughput, low‑latency systems – ideally streaming or real‑time decisioning.
• Experience in a startup‑mode team or within a larger company: small teams, shifting priorities, owning things end‑to‑end.
• Polyglot and curious – comfortable working in several languages and eager to pick up new ones, frameworks, and tools as the problem demands.
• Proficient with AI tools (e.g., Claude Code, Copilot) and use them regularly, not just once.
• Clear, concise code and written communication; able to explain designs to engineers and product managers.
• Cares about quality – tests, observability, and clean interfaces are non‑negotiable.
• Collaborates well with engineers, data scientists, and product partners.

Show real hands‑on experience in several of the following areas:

• Decisioning Data & Features: lake houses, delta lakes, distributed logs; feature platforms, data models, data contracts, lineage, and quality checks.
• High‑Throughput, Low‑Latency Systems: event streaming, high‑volume pipelines, distributed caches, sub‑second transaction processing, rules engines.
• AI & ML Systems: model training, deployment, refreshing, low‑latency inference, LLM integration, prompt engineering, model monitoring.
• Decisioning Tooling: authoring, testing, deploying business rules; tools for authors to validate rules and models; operator workflows for approvals, observability, and explanation.
• Cloud & Dev Ops: AWS and cloud‑native patterns; CI/CD, automation, observability, Git Ops.

• Several years of software engineering experience with real contributions to complex systems or shared platforms.
• Hands‑on experience with distributed systems running at high throughput and sub‑second latency; understanding of multi‑region availability, consistency, back pressure, and capacity.
• Solid grasp of modern software engineering practices, cloud‑native architectures, and AI/data platforms.
• Clear communicator who works well across teams.
• Bachelor's degree in Computer Science, Software Engineering, or a related field – or equivalent experience. Advanced degrees are a plus, not required.

• Abide by Mastercard’s security policies and practices.
• Ensure the confidentiality and integrity of the information being accessed.
• Report any suspected information security violation or breach.
• Complete all periodic mandatory security trainings in accordance with Mastercard’s guidelines.

Competitive base salary, possible annual bonus or commission. Benefits include medical, prescription drug, dental, vision, disability, life insurance; flexible spending and health savings accounts; paid leave (new‑parent, bereavement, sick, vacation); 401(k) with employer match; deferred compensation for eligible roles; fitness reimbursement or on‑site fitness facilities; tuition reimbursement; and more.

O'Fallon, Missouri: $115,000 – $184,000 USD