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 strategic, while bringing clarity and technical stability to ambiguous challenges and prioritizing work that enables the team to move faster. Technologies we use (not exhaustive): HTML, TypeScript, JavaScript, React Python, Django MySQL, Cassandra, RabbitMQ, Redis Amazon Web Services (EC2, RDS, Aurora, etc.), Terraform, Ansible, Packer, and other DevOps tools We use Covey as part of our hiring and / or promotional process. For jobs or candidates in NYC, certain features may qualify it as an AEDT. As part of the evaluation process we provide Covey with job requirements and candidate submitted applications. We began using Covey Scout for Inbound on April 3, 2025. Please see the independent bias audit report covering our use of Covey here 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: $148,000 — $222,000 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 for payment, bank details, or personal financial information as part of the application process. All our legitimate job postings can be found on our official career site. Please be cautious of job offers that come from non-company email addresses (@klaviyo.com), instant messaging platforms, or unsolicited calls. By clicking "Submit Application" you consent to Klaviyo processing your Personal Data in accordance with our Job Applicant Privacy Notice. If you do not wish for Klaviyo to process your Personal Da