Senior Software Engineer, Experimentation & Optimization

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 careers.klaviyo.com to see how we empower creators to own their own destiny.
Klaviyo operates a real-time data analytics platform, built primarily in Python and hosted on Amazon Web Services (AWS), scalable by design to meet increasing demand. Engineers at Klaviyo bring experience from diverse backgrounds and disciplines, contributing to a collaborative and high-impact environment.
The Experimentation & Optimization team is a full-stack engineering team that builds intuitive and robust experimentation solutions for Klaviyo users. Our team is responsible for developing and enhancing Klaviyo's experimentation platform, enabling users to experiment with and optimize campaigns, flows, and forms to improve audience engagement. We prioritize rigorous statistical methods and ensure model explainability, working closely with data scientists and UX designers to create a seamless user experience. By providing a powerful platform, expert guidance, in-depth analysis, and actionable insights, we help businesses extract meaningful learnings from their data. Our work integrates deeply with Klaviyo's core technologies, requiring close collaboration across the engineering organization to build scalable, data-driven solutions.
We are looking for a Senior Software Engineer to design and build experimentation features that empower Klaviyo customers to make data-driven decisions. You'll play a critical role in technical discussions around how we architect scalable and statistically rigorous systems. You'll own key projects that contribute to the team's mission and roadmap, working closely with product managers, analysts, and other engineers to deliver impactful solutions. Your work will directly influence how customers test and optimize their marketing strategies.
Our tech stack includes

• Python, FastAPI, gRPC, TypeScript, React, AWS, Django, and Spark.
• MySQL, PostgreSQL, Clickhouse, Redis, DynamoDB
• AWS, Terraform, Docker, Argo

How You Will Make a Difference

• Build and deliver experimentation and optimization capabilities that help Klaviyo users test and improve their marketing strategies.
• Design and implement scalable systems that support a wide range of experiment types across campaigns, flows, and forms.
• Contribute to the evolution of Klaviyo's experimentation infrastructure, working with large-scale data to deliver meaningful insights for businesses of all sizes.
• Collaborate cross-functionally with product, design, and data science to create a seamless and statistically rigorous experimentation experience.
• Grow your expertise in experimentation methodologies and help influence best practices across teams.

Who You Are

• 5+ years of experience as a full stack engineer, preferably within a SaaS product environment.
• Experience developing intuitive, consistent APIs in either REST or GraphQL
• Strong understanding of scalable web and data architectures, with experience designing or building experimentation or optimization features.
• Demonstrated success delivering complex projects that span multiple sprints or quarters.
• Familiarity with experimentation platforms, statistical analysis, or MLOps practices.
• Curious, impact-driven, and excited to dive into challenging technical domains to help shape core product capabilities.

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.
The pay range for this role is listed below. Some sales and success roles are also eligible for variable compensation and hourly non-exempt roles are eligible for overtime in accordance with applicable law. This role is eligible for benefits, including: medical, dental and vision coverage, health savings accounts, flexible spending accounts, 401(k), flexible paid time off and company-paid holidays and a culture of learning that includes a learning allowance and access to a professional coaching service for all employees.
Base Pay Range For US Locations:
$152,000 - $228,000 USD
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.
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.
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