Senior Software Engineer, Backend (AI Platform)

About this role

Build and operate Affirm’s AI platform services, including gateways, agent runtime, and evaluation systems. Help scale AI workloads securely and reliably while providing governance, cost attribution, and operational controls.

About the company

Affirm offers buy now, pay later financing that lets consumers split purchases into transparent installment payments at checkout. It partners with merchants to provide flexible credit options without late fees.

The team

AI Platform team

Stack

What you'll do

• Own technical decisions and projects from design through launch and on-call.
• Build gateway, runtime, and evaluation services for production AI workloads.
• Develop identity, quota, routing, caching, and failover controls for AI usage.
• Partner with security, infrastructure, and product engineering on agent guardrails and tool-access identity.
• Monitor system health and maintain alerts, runbooks, and on-call practices.
• Improve design and code review standards, and mentor engineers.

What we're looking for

• At least 4 years designing, building, and launching scalable backend systems.
• Experience developing highly available distributed systems with technologies such as AWS, MySQL, and Kubernetes.
• Practical production experience with LLMs, agents, or AI frameworks.
• Ability to plan and deliver significant system components with simple, extensible designs.
• Strong coding, communication, and cross-team collaboration skills.

Nice to have

• Experience with LLM gateways such as LiteLLM, MCP, tool calling, evaluations, or agent runtimes.

Benefits

• 100% subsidized medical, dental, and vision coverage for employees and dependents.
• Monthly technology, health, and wellness spending stipends.
• Flexible time off and generous holidays.
• Employee stock purchase plan with a stock discount.