Senior Software Engineer, Backend (AI Platform)

About this role

Build and operate the AI platform that enables Affirm teams to safely develop, evaluate, and run AI workloads in production. The role focuses on scalable gateways, agent runtimes, and evaluation services, with ownership from design through launch and on-call.

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

• Design, build, and operate AI gateway, runtime, and evaluation services.
• Develop identity, quota, routing, caching, and failover controls for AI workloads.
• Partner with security, infrastructure, and product teams to establish agent guardrails and tool-access identity.
• Own system metrics, monitoring, alerting, runbooks, and on-call health.
• Set technical plans and improve design, code review, and engineering standards.
• Mentor engineers and use AI tools and agentic workflows in daily engineering work.

What we're looking for

• 4+ years designing, developing, and launching backend systems at scale.
• Experience building highly available distributed systems with technologies such as AWS, MySQL, and Kubernetes.
• Production experience with LLMs, agents, or AI frameworks, such as inference APIs, gateways, MCP, tool calling, evaluations, or agent runtimes.
• Ability to design and deliver significant system components and make safe changes in large codebases.
• Strong written and verbal communication skills.

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 discount.
• Equity rewards may be included in total compensation.