Senior Software Engineer, Backend (AI Platform)

About this role

Build and operate AI platform services that help Affirm teams safely take AI workloads from pilot to production. The work includes model and tool gateways, agent runtime, and evaluation and observability systems, with a focus on reliability, security, and cost governance.

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, launch, and operate AI gateway, runtime, and evaluation services.
• Develop identity, quota, routing, caching, and failover controls for AI usage.
• Collaborate with security, infrastructure, and product engineering on agent guardrails and tool access.
• Own system monitoring, alerting, runbooks, and on-call health.
• Set code review and design standards, and mentor engineers.

What we're looking for

• At least 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.
• Ability to design and deliver significant system components with clear, extensible designs.
• 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 technology and health and wellness stipends.
• Flexible time off and generous holiday calendars.
• Employee stock purchase plan with a discount.