Sr. Lead Software Engineer - Mobile Channels at Klaviyo

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 Mobile Channels Team: The Mobile Channels team at Klaviyo powers text messaging across Klaviyo's platform — SMS, RCS, WhatsApp, and a growing set of future text messaging channels. Mobile is one of Klaviyo's fastest-growing product areas: as brands shift more of their owned-channel investment to mobile, our team builds the infrastructure that makes high-throughput, reliable delivery possible across a complex, multi-channel landscape. We own the systems that connect Klaviyo customers to their audiences through the fastest and most personal communication channels available — at scale, across geographies, and against a constantly evolving set of carrier, regulatory, and provider constraints. As a Senior Lead Software Engineer on the Mobile Channels team, you'll be the technical area lead for Mobile Channels — driving architecture and technical direction across the SMS, RCS, and WhatsApp teams, and the new channels we'll add next. You'll define the cross-team technical roadmap for the pillar, own the architectural patterns that bind the channels together (ingestion, routing, provider integration, status tracking, compliance automation, deliverability), and lead the most complex, multi-team initiatives end-to-end. This is a hands-on technical leadership role: you'll contribute to architecture and code, lead design reviews, mentor Lead and Senior engineers across multiple teams, and partner closely with Engineering Managers to keep our systems healthy as the surface area grows. If you're excited about being the senior IC who connects the technical strategy across an entire multi-channel messaging pillar — and doing it at one of Klaviyo's highest-growth product areas — Mobile Channels is the place to do it. How You Will Make a Difference: • Technical Strategy & Roadmap: Define and drive the cross-team technical roadmap for Mobile Channels, aligning architectural direction across SMS, RCS, WhatsApp, and emerging channels with company priorities and the broader Messaging Infrastructure strategy. • Multi-Team Architecture: Own the architectural patterns that span the pillar — message ingestion and routing, provider integration, status tracking, deliverability, opt-in/opt-out and compliance automation, multi-region readiness — and embed them into team roadmaps, not just documents. • Hands-On Technical Leadership: Stay in the code. Drive architecture and design across teams, lead high-stakes design reviews, build prototypes and reference implementations to de-risk decisions, and ship meaningful contributions yourself. • Reliability & Scale: Raise the bar on reliability across Mobile Channels — drive systemic fixes for recurring incidents, lead deep dives on the highest-impact production issues, and embed stronger guardrails (end-to-end testing in CI, readiness gates, observability standards) into how the teams ship. • Cross-Functional & Cross-Pillar Collaboration: Partner with Engineering Managers, Product, Deliverability, Compliance, and Platform leadership to sequence cross-team work realistically. Build durable peer relationships with senior technical leaders across Klaviyo's other engineering pillars to drive company-wide technical objectives that span multiple pillars — bringing the Mobile Channels perspective to those forums, and connecting our roadmap to the broader engineering strategy. • AI-Forward Engineering: Put AI at the center of how the teams build and how the systems run — model AI-fluent engineering practices yourself, and drive concrete improvements to operational and developer workflows (anomaly detection, synthetic load, runbook automation) across the teams. • Mentorship: Mentor other engineers regularly, primarily experienced lead and senior engineers across SMS, RCS, and WhatsApp, and represent Mobile Channels' technical bar in senior hiring. • Continuous Improvement: Stay current with how the messaging ecosystem and engineering craft are evolving — new channels, carrier and regulatory shifts, AI tooling, performance and reliability practices — and translate that into concrete, sequenced improvements for the teams. Who You Are: • Experience: 12+ years of software engineering experience with a strong track record building and scaling distributed backend systems. Prior time as a Lead, Staff, or Principal engineer driving technical direction across multiple teams. • Hands-On Technical Depth: Proficient in Python and/or Go, and able to rapidly learn the other. Comfortable coding, reviewing, and debugging complex systems — this is a hands-on role. • Distributed Systems Expertise: Deep experience with high-throughput, event-driven, distributed architectures — ingestion pipelines, async processing, stateful workloads, eventing patterns, multi-region/data-locality concerns, and the failure modes that come with all of it. • Architectural & Strategic Skills: Demonstrated ability to define technical strategy and drive cross-team architectural decisions in ambiguous, high-stakes environments — and to commit to a call even when there's disagreement, backed by data and prototypes. • Cloud & Platform: Strong experience with AWS at scale; comfortable with Infrastructure as Code (Terraform), containerization, and modern observability stacks (metrics, logs, traces, SLI/SLO design). • Business & Product Mindset: You think beyond the code — you understand customer impact, commercial value, and the cost-vs-conversion tradeoffs that come with mobile messaging — and you bring that mindset into architectural decisions. • Influence & Communication: Exceptional communicator; can articulate complex technical concepts to engineers, product leaders, and executives, and can rally multiple teams toward sequenced, realistic improvements. • AI Enthusiast: You've already experimented with AI in work or personal projects, and you're excited to dive in and learn fast. You're hungry to responsibly explore new AI tools and workflows, finding ways to make your work — and the systems you build — smarter and more efficient. • Collaborative & Self-Led: Strong cross-functional partner; thrives in a hybrid team and high-autonomy environment; ships value early and iterates. Nice to Have: • Experience with the SMS, RCS, or WhatsApp ecosystems, including channel-specific protocols, opt-in/opt-out semantics, and familiarity with key 3rd-party entities (carriers, providers, regulators) and compliance rules and best practices. • Background in performance optimization and a passion for digging into performance, scalability, and reliability issues to drive breakthrough solutions across distributed systems. • Experience with multi-region deployments, data residency, and large-scale data or service migrations with minimal downtime. • Familiarity with complex data management for testing, including large datasets and production-like data replication. Technologies We Use: • Python, Go • AWS, Terraform, DynamoDB, Redis, SQL • Kafka Location: This is a hybrid role based in Boston, with 3 days in office and 2 days remote per week. 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 USDThis 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 Data, please do not submit an application. You can find our Job Applicant Privacy Notice here and here (FR).