Senior Software Engineer, Backend (AI Platform)

Location: Remote US; most roles can be performed almost anywhere within the country of employment. Occasional in-person work at an Affirm office may be required, and all new hires attend in-person onboarding.

Base pay: $195,000–$255,000 per year in CA, WA, NY, NJ, and CT; $173,000–$233,000 per year in other U.S. states.

Company

Affirm provides transparent, predictable payment products and builds large-scale infrastructure for financial products, merchants, and vendors.

What you will do

• Own technical decisions and projects across design, launch, operations, and on-call support.
• Design and build AI gateways, agent runtimes, and evaluation services that scale AI workloads to production.
• Implement identity, quota, routing, caching, failover, cost attribution, and governance controls for models and tools.
• Partner with security, infrastructure, and product engineering teams on agentic-workload guardrails and on-behalf-of identity for tool access.
• Own operational health through metrics, monitoring, alerting, runbooks, and on-call practices.
• Improve code review and design standards, use AI-native workflows, mentor engineers, and promote engineering best practices.

Requirements

• 4+ years of experience designing, developing, and launching backend systems at scale using Python or Kotlin.
• Experience developing highly available distributed systems with technologies such as AWS, MySQL, and Kubernetes.
• Production experience building with LLMs, agents, or AI frameworks, including inference APIs, LLM gateways such as LiteLLM, MCP, tool calling, evals, or agent runtimes.
• Understanding of AI usage and the infrastructure required to support and leverage AI workloads across disciplines.
• Experience defining technical plans for significant features or system components using elegant, simple, and extensible designs.
• Ability to write high-quality, understandable code and safely make significant changes in a large codebase.
• Ownership of professional growth and proactive feedback-seeking from teams, managers, and stakeholders.
• Strong verbal and written communication skills for collaboration with a global engineering team.
• Equivalent practical experience or a Bachelor’s degree in a related field.

Culture & Benefits

• Remote-first work with flexibility within the country of employment.
• Blameless postmortems, detailed technical specifications, and feedback-driven engineering practices.
• 100% subsidized medical coverage, dental and vision coverage for employees and dependents.
• Monthly technology, health, and wellness spending stipends.
• Flexible time off, generous holiday calendars, and an employee stock purchase plan.
• Inclusive interview process with accommodations available for candidates with disabilities.