Senior Backend Software Engineer (AI Platform)

Join Affirm's engineering team as a Senior Backend Software Engineer (AI Platform). You will be responsible for building and maintaining large-scale, fault-tolerant infrastructure for multiple financial products. The AI Platform team focuses on creating a paved path for building, running, evaluating, and governing AI systems. You will design and build gateway, runtime, and evaluation services, partner with security and infrastructure teams, and own the operational health of the systems you ship. Additionally, you will mentor and grow engineers on the team and advocate for best practices in design, coding, and testing.

- Plan, execute, and own technical decisions and projects within the AI Platform team, from design through launch and on-call. - Design and build gateway, runtime, and evaluation services to take AI workloads from pilot to production, securely scaling across millions of users and their transactions. - Partner with security, infrastructure, and product engineering teams to set guardrails for agentic workloads and the on-behalf-of identity model for tool access.

- Practical experience building with LLMs, agents, or AI frameworks in production, such as inference APIs, LLM gateways (LiteLLM or similar), MCP, tool calling, evaluations, or agent runtimes - A demonstrated commitment to your own growth, including proactively seeking feedback from your team, manager, and stakeholders - Proficiency making significant changes in a large codebase, with a suite of tools and practices that enable you and your team to do so safely - An understanding of AI usage and the infrastructure needed to support and leverage AI workloads across different disciplines - Equivalent practical experience or a bachelor’s degree in a related field - 4+ years of experience designing, developing, and launching backend systems at scale using languages such as Python or Kotlin - Experience defining a technical plan to deliver a significant feature or system component with an elegant, simple, and extensible design, and writing high-quality code that is easy for others to understand and use - Strong verbal and written communication skills to support effective collaboration with a global engineering team - A track record of developing highly available distributed systems using technologies such as AWS, MySQL, and Kubernetes