Senior Software Engineer, Backend (AI Platform)

About this role

Build and operate Affirm’s AI platform services, including model and tool gateways, agent runtime, and evaluation systems. Help scale AI workloads into secure, reliable production systems while adding governance for identity, cost, routing, and access.

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 teams on agent guardrails and tool access
• Monitor system health and maintain alerts, runbooks, and on-call operations
• Set design and code review standards and mentor engineers

What we're looking for

• 4+ years designing, developing, and launching scalable backend systems
• Experience building highly available distributed systems with technologies such as AWS, MySQL, and Kubernetes
• Production experience with LLMs, agents, or AI frameworks
• Ability to design and deliver significant system components
• Strong written and verbal communication skills

Nice to have

• Experience with LLM inference APIs, gateways, MCP, tool calling, evaluations, or agent runtimes

Benefits

• 100% subsidized medical, dental, and vision coverage for employees and dependents
• Monthly tech, health, and wellness stipends
• Flexible time off and generous holidays
• Employee stock purchase plan with discounted shares