Senior Software Engineer, Backend (Cost Engineering)

About this role

At Affirm, we exist for the moments that matter—giving people a clear, predictable way to pay over time, with no hidden fees, no surprises, and no tradeoffs on what matters most. The Capacity Modeling team ensures Affirm can safely handle forecasted traffic—especially during peak sales events—by translating demand forecasts into concrete, testable capacity plans. They build and maintain statistical capacity models that map traffic inputs (e.g., checkout volume, app opens, batch/job activity) to resource outputs (CPU, memory, connections) and then convert those forecasts into recommended capacity settings such as pod counts, HPA ranges, and/or infrastructure sizing changes across regions and environments.

What You'll Do · You will be responsible for owning and delivering quarterly goals for your team, leading engineers on your team through ambiguity to solve open-ended problems, and ensuring that everyone is supported throughout delivery. · You will support your peers and stakeholders in the product development lifecycle by collaborating with product management, design & analytics by participating in ideation, articulating technical constraints, and partnering on decisions that properly consider risks and trade-offs.

· You will proactively identify project, process, technology or business issues, advocate for them, and lead in solving them. · You will support the operations and availability of your team’s artifacts by creating and monitoring metrics, escalating when needed, and supporting “keep the lights on” & on-call efforts. · You will foster a culture of quality and ownership on your team by setting or improving code review and design standards for your team, and advocating for them beyond your team through your writing and tech talks.

· You will help develop talent on your team by providing feedback and guidance, and leading by example. What We Look For · You have 4+ years of experience designing, developing and launching backend systems at scale using languages like Python or Kotlin. · You have a track record of developing highly available distributed systems using technologies like AWS, MySQL and Kubernetes. · You have experience supporting scale up and down of large scale sales event such as Prime Day, Black Friday Cyber Monday, or other sales holidays · You have tuned autoscaling, CPU/Memory, and multi-threading for compute type workloads.