Senior Software Engineer - Growth

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. Why You Should Join the Onboarding Team The [Product Expansion / Activation] team at Klaviyo is focused on improving the early experience of Klaviyo for new customers. We work diligently to improve the rate at which customers are successfully setting up their Klaviyo account and gaining value from the platform. Engineers on the team use data to discover opportunities for improvement, implement A/B tests to validate ideas, and work across the product to iteratively improve UX and reduce friction for new customers. We are looking for great generalist software engineers with a passion for the experience-layer that have an interest in or experience with growing a user-base and building a great customer onboarding pipeline and experience. How You Will Make a Difference • In this role, you will drive the technical design and lead the implementation of high-impact user-experience improvements across the Klaviyo product, focusing on areas critical to new customer success and adoption. You will own the entire project lifecycle, working through ambiguity and requirements refinement to execution and delivery. • You will own the end-to-end experimentation process, including contributing to the definition of strategy, architecting and implementing A/B tests to validate product hypotheses, and interpreting data to drive significant iterative improvements. You will be accountable for the quality and operational health of the features you deliver. • You will serve as a technical leader and liaison, collaborating proactively with partners across teams to define and prioritize key technical initiatives to shape the long-term product roadmap. • You will take a lead role in mentoring and providing technical guidance to other engineers on the team, elevating our experimentation, development, and operational practices, ensuring contributions consistently leave the product area better than when you found it. • You will define the architectural approach and technical strategy for your area of responsibility, anticipating scalability and reliability needs, including leveraging AI agents in our work and delivery, ensuring the solution is robust, scalable, and adheres to best practices for security, performance, and maintainability. • Working from our Boston HQ 5 times per week Who You Are • Have an extensive background in full stack software engineering, demonstrating deep understanding of Klaviyo’s systems and the ability to architect, deliver, and maintain software with an emphasis on high-scale, user-facing features, and their supporting APIs and infrastructure. • Demonstrated ability to drive technical strategy and improvement using a data-driven mindset, leading to measurable business results and upholding best practices. • Demonstrated technical experience in using and championing AI-driven software delivery practices and methods, a passion for continuous learning and mentoring, and the ability to work productively through others to set them up for project success. • Experience driving A/B testing strategies for products with metric-based goals to significantly improve user experience, customer acquisition, and success is a strong plus. • Thrives in an entrepreneurial type environment that is customer focused and stra