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. Senior Lead Engineer, Applied AI (Customer Agent) About the Team: Our Engineering team builds the AI systems that power how brands run their businesses on Klaviyo. We move fast, ship in production, and hold a high bar for what "AI-native" actually means: systems that make real judgment calls, not demos. The Customer Agent team is one of the newest and most ambitious groups in that org, based in Boston and working in-office: we're building a conversational AI system that lets brands serve their own customers at a scale no human support team could match. We're still small enough that a single senior engineer can shape how the whole platform evolves. We're past the demo stage: the team ships changes against live customer traffic, measures quality with real evaluation frameworks, and treats reliability as a product feature, not an afterthought. About the Role: As Senior Lead Engineer, you'll set technical and product direction for Customer Agent end to end, building a 0-to-1 agentic product with the speed and ownership of a startup, backed by the scale and resources of one of the most innovative tech companies on the East Coast, while staying hands-on with the hardest problems yourself. This is a principal-caliber individual contributor role: we're looking for an engineer who has personally architected, built, scaled, and supported a production agentic system through everything that comes after the demo, and who acts as a force multiplier across the org through the strength of their technical judgment. How You'll Make an Impact: • Set the technical and product direction for Customer Agent's core platform, from architecture through production. • Take on the platform's hardest technical problems personally: orchestration, evaluation, guardrails, memory & context, self-healing/improving and failure handling for non-deterministic systems. • Write and ship code, review designs, and make the calls other engineers can't make alone. • Build architecture and frameworks that other engineers and teams adopt, and mentor through design reviews rather than direct management. • Partner with product, design, data science, and go-to-market leaders to shape the roadmap, not just execute against it. • Evaluate emerging AI technologies and bring the ones worth betting on into production. What We're Looking For: • You've architected, built, scaled, and supported a production agentic system end to end, not just prototyped one: real orchestration, evals, guardrails, and non-deterministic failure handling. You've owned it through launch, scale, incidents, and the years of operational reality after the demo. • You've learned the hard lessons that only come from running agents in production: securing them against misuse and abuse, and the operational scar tissue of keeping a non-deterministic system reliable as usage grows. • You've set technical and product direction for an entire product area before, not just your own component, and you can point to something you designed and championed that shipped and that other teams built on. • You've stayed hands-on through all of it: still writing code, reviewing your own architecture decisions, and debugging production issues yourself, not delegating the hardest problems away. • Your past architecture and frameworks got reused by other teams, and you've unblocked multiple teams at once, not just your own. • You communicate complex technical trade-offs clearly across engineering, product, and executive audiences, and you can turn an undefined problem into a plan others rally behind. Nice to Haves: • Experience running a multi-tenant agent platform at production scale, where external customers configure their own agent behavior on shared infrastructure. • Experience building 0-to-1 products or working in startup environments. • A track record with production evaluation systems, AI observability, or human-in-the-loop workflows for LLM-powered products. Boston, MA – In-Office Role - 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 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 Notic…