Senior Software Engineer - Infrastructure
About SixtyfourSixtyfour helps teams understand the people, companies, and entities they interact with. With a primary focus on Compliance (AML/KYB), Trust & Safety, Cybersecurity, and Investigations. Our platform combines agents, LLMs, and large-scale data infrastructure to surface data other platforms can't.The RoleWe're looking for a Senior Software Engineer to join our core Engineering team and help build the infrastructure Sixtyfour runs on. This is a hands-on, high-ownership role spanning backend systems, API design, billing, and infra scaling. This is the kind of work that shapes not just what we ship, but how we build for years to come. You won't have direct reports, but you'll operate as a technical leader from day one: setting the standards, shaping architecture decisions, and mentoring engineers as the team grows around you.If you're the kind of engineer who gets excited about API design, scaling infrastructure, and payments/billing systems, let’s talk.What You'll DoOwn and evolve core backend infrastructure as we scale usage and trafficDesign and build robust, well-architected APIs that power our core product and developer platformBuild and maintain billing and payments infrastructure (Stripe)Build and productionize agent workflows and LLM-powered systemsDrive technical decisions around scaling — performance, reliability, data pipelines, and searchOperate like an SRE when needed.Work hands-on in the codebase daily while mentoring other engineers and helping raise the technical bar across the teamPartner directly with leadership on technical strategy and roadmap as an early, influential member of the teamWhat We're Looking For3–7 years of professional software engineering experienceExperience as a team lead or tech lead — comfortable providing technical direction and mentorship without needing direct reports to do soStrong API design and backend development experienceExperience with observability Experience with backend infrastructure and scaling systems in productionExperience building or maintaining billing/payments systems (Stripe or similar)Proficiency in Python and JavaScriptExperience with KubernetesExperience with Apache SparkExperience with AWS: Glue, EC2, Data Pepper & CloudWatchExperience with: Temporal Experience with OpenRouterExperience with LLMs, scaling infrastructure, and searchComfortable in a fast-paced, early-stage environment with high ownership and ambiguityWilling to be based in or relocate to the San Francisco Bay Area.Nice to HaveExperience building developer-facing products or platforms (APIs, SDKs, dev tools)Experience with Next.js and VercelPrior startup experience, ideally at a similarly early stageExperience working in an AI companyExperience developing agentsBenefitsUnlimited PTOLunch on us in the officeMonthly gym membership reimbursementMonthly AI tools/productivity reimbursement401k with company matchHealth / Dental / Vision Flexible working hours