At Klaviyo, we value the unique backgrounds, experiences and perspectives each Klaviyo (we call ourselves Klaviyos) brings to our workplace each and every day. We believe everyone deserves a fair shot at success and appreciate the experiences each person brings beyond the traditional job requirements. If you’re a close but not exact match with the description, we hope you’ll still consider applying. Want to learn more about life at Klaviyo? Visit klaviyo.com/careers to see how we empower creators to own their own destiny. Job Title: Sr. Lead Software Engineer Location: Boston, MA This role is based in our Boston hub. We operate a hub‑first model, with regular in‑office collaboration expected. About the Role At Klaviyo, we believe the future of software isn’t just better productivity tools for humans—it’s intelligent systems that can run, optimize, and adapt themselves based on real-time outcome and reward signals. Having already built the infrastructure and applications that connect businesses with over 200,000 customers, billions of consumer profiles, and hundreds of billions of interaction events, we are now making foundational investments in Marketing AI and Service AI to power next-generation agentic capabilities across our entire ecosystem. The Klaviyo Orchestrate pillar drives the core platform experience, providing the high-throughput capabilities our customers use daily to manage and execute complex marketing workflows. This team balances strict Tier-1 availability and low-latency scalability requirements with rapid agility across the Klaviyo ecosystem. Internally, we have fully embraced AI-native engineering methodologies and are dedicated to putting sophisticated AI-native capabilities directly into the hands of our builder-customers. We are building a best-in-class, flexible orchestration platform designed to handle massive scale while continuously advancing reliability and performance to meet the expanding needs of our global customer base. How You’ll Make a Difference • Architect and scale Klaviyo’s Core Orchestration platform, supporting high-traffic, low-latency services with extreme reliability. • Drive the technical vision for integrating AI-driven agentic workflows and automated decision-making into core customer interactions. • Lead the adoption of AI-native software development practices, continually improving engineering productivity and delivery speed across the team. • Design foundational frameworks and services adopted across engineering teams, championing high technical standards through design reviews and mentorship. • Partner closely with product management, data science, design, and executive leaders to shape strategic roadmaps and long-term platform architecture. Who You Are • Experienced Backend Leader: 8+ years of professional software engineering experience centered on distributed systems, microservices architecture, and high-availability backend platform ownership. • AI & Agentic Systems Practitioner: Hands-on experience shipping production LLM workflows, retrieval-augmented generation (RAG) pipelines, or agentic frameworks with a solid understanding of evals, prompt architecture, and fine-tuning. • Distributed Systems Specialist: Proven track record of architecting event-driven architectures, asynchronous processing pipelines, and message queues (e.g., Kafka, Celery, SQS, Redis) for heavy throughput workloads. • Python & Tooling Mastery: Deep proficiency in Python and modern frameworks (FastAPI, Django) alongside experience with data processing platforms and object-relational mapping tools. • Cloud Infrastructure Native: Strong expertise with AWS, Kubernetes, CI/CD automation, and modern observability suites, integrating cloud architecture seamlessly into system design. • Quality & Evals Focused: Experience establishing automated evaluation frameworks for AI models, balancing latency, accuracy, cost, and safety in production environments. • Cross-Functional Influencer: A technical leader who elevates team performance through architectural direction, collaborative problem-solving, and clear communication across engineering and business domains. • Collaborative and customer‑first. You’re comfortable collaborating directly with PMs, ML engineers, and customers; you can translate between customer needs, product goals, and technical constraints, and you care deeply about the customer experience. • AI-First Engineer: Active use of AI coding tools and modern agentic development workflows in daily work to accelerate innovation and shorten feedback cycles. • Customer-Centric Mindset: Driven by user outcomes, with a knack for translating complex customer needs into resilient software architecture. Nice to Haves • Experience designing or integrating shared AI/ML platforms consumed by multiple internal engineering teams. • Domain expertise in MarTech, e-commerce platforms, personalization engines, or real-time event streaming. Massachusetts Applicants: It is unlawful in Massachusetts to require or administer a lie detector test as a condition of employment or continued employment. An employer who violates this law shall be subject to criminal penalties and civil liability. Our salary range reflects the cost of labor across various U.S. geographic markets. The range displayed below reflects the minimum and maximum target salaries for the position across all our US locations. The base salary offered for this position is determined by several factors, including the applicant’s job-related skills, relevant experience, education or training, and work location. In addition to base salary, our total compensation package may include participation in the company’s annual cash bonus plan, variable compensation (OTE) for sales and customer success roles, equity, sign-on payments, and a comprehensive range of health, welfare, and wellbeing benefits based on eligibility.  Your recruiter can provide more details about the specific salary/OTE range for your preferred location during the hiring process. Base Pay Range For US Locations: $216,000—$324,000 USD This role may require up to 10% travel for purposes such as new hire onboarding, client or partner work if applicable, team meetings, and industry events. Travel is coordinated in advance. Get to Know Klaviyo We’re Klaviyo (pronounced clay-vee-oh). We empower creators to own their destiny by making first-party data accessible and actionable like never before. We see limitless potential for the technology we’re developing to nurture personalized experiences in ecommerce and beyond. To reach our goals, we need our own crew of remarkable creators—ambitious and collaborative teammates who stay focused on our north star: delighting our customers. If you’re ready to do the best work of your career, where you’ll be welcomed as your whole self from day one and supported with generous benefits, we hope you’ll join us. AI fluency at Klaviyo includes responsible use of AI (including privacy, security, bias awareness, and human-in-the-loop). We provide accommodations as needed.  By participating in Klaviyo’s interview process, you acknowledge that you have read, understood, and will adhere to our Guidelines for using AI in the Klaviyo interview Process. For more information about how we process your personal data, see our Job Applicant Privacy Notice. Klaviyo is committed to a policy of equal opportunity and non-discrimination. We do not discriminate on the basis of race, ethnicity, citizenship, national origin, color, religion or religious creed, age, sex (including pregnancy), gender identity, sexual orientation, physical or mental disability, veteran or active military status, marital status, criminal record, genetics, retaliation, sexual harassment or any other characteristic protected by applicable law. IMPORTANT NOTICE: Our company takes the security and privacy of job applicants very seriously. We will never ask fo…