Staff Software Engineer, Backend (Capacity Modeling)

Affirm is reinventing credit to make it more honest and friendly, giving consumers the flexibility to buy now and pay later without any hidden fees or compounding interest. 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. This Staff Engineer role focuses on setting technical strategy, driving operational excellence, and mentoring a high-performing backend engineering team.

About the Role

As a Staff Software Engineer on the Capacity Modeling team, you'll own the technical vision and execution of systems that map traffic inputs (checkout volume, app opens, batch/job activity) to resource outputs (CPU, memory, connections). Your work directly impacts Affirm's ability to scale safely across peak demand periods. You'll build and maintain statistical capacity models, convert forecasts into infrastructure recommendations (pod counts, HPA ranges, regional sizing), and cover infrastructure resources including Compute, ElasticCache, DynamoDB, and AuroraDB.

Responsibilities

• Define and execute year-long technical strategy for your team, aligned with business-critical projects
• Collaborate with product management, design, and analytics teams to ensure technical sustainability and manage risks and trade-offs
• Act as a force-multiplier by advocating for technical solutions and operational processes across the organization
• Own your team's operations and availability through monitoring, triage rotations, playbooks, policies, testing, and alerting
• Establish and champion code review and design standards, promoting quality culture beyond your team
• Develop talent through feedback, guidance, and leading by example

Requirements

• 8+ years designing, developing, and launching backend systems at scale with Python or Kotlin
• Proven track record building highly available distributed systems using AWS, MySQL, Spark, and Kubernetes
• Experience supporting large-scale sales events (Prime Day, Black Friday Cyber Monday, or equivalent)
• Hands-on expertise tuning autoscaling, CPU/memory, and multi-threading for compute workloads
• Demonstrated ability to deliver major features, system components, or deprecations through technical planning and execution
• Ability to write high-quality, easily understood code and thrive in ambiguity

Benefits

Remote US position.