Lead Software Engineer, Real-Time Messaging Systems

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.

About Klaviyo

Klaviyo is a leading marketing automation platform that helps businesses grow by delivering personalized experiences. Our mission is to empower creators to own their destiny. We believe in providing an exceptional developer experience that enables our engineering teams to build and ship high-quality software efficiently and with confidence.

About the Team

The Messaging Infra organization at Klaviyo is focused on high-growth customer engagement through various messaging channels (email, SMS/MMS/RCS, mobile push, WhatsApp, and more). We work with multiple stakeholders to provide best-in-class service to connect a wide range of businesses, from entrepreneurs to enterprises, with their end users. The messaging platform is a mission-critical, event-driven system, responsible for delivering billions of real-time, low-latency messages, and must be architected for massive scale.

As a Lead Software Engineer in the Messaging Infrastructure organization, you'll provide technical leadership to a group of engineers building and scaling the live, event-driven services that power Klaviyo's messaging pipeline end-to-end. You'll drive technical strategy for a system where every message is a real-time event with a customer's business outcome riding on it, own critical components of the delivery infrastructure, and help the team navigate the unique challenges of multi-channel compliance, regulatory requirements, provider integrations, and global deliverability. This is a hands-on technical leadership role where you'll contribute to architecture, code, and mentorship while shaping the future of messaging at Klaviyo.

How you will make a difference

Lead a team of engineers building and scaling highly-available, low-latency, high-throughput services across one or more messaging channels

Own and drive the architecture of key components in Klaviyo's messaging pipeline — from ingestion and routing through to delivery and status tracking

Design and implement scalable backend services in Python and/or Go, built to hold up under real-time, unpredictable load rather than scheduled batch windows

Work on a campaign pipeline that processes and delivers hundreds of millions of messages daily, growing to billions-scale, with peak throughput measured in messages per second and performance tracked against p99 latency, not just daily volume

Make real-time architectural tradeoffs on backpressure, delivery guarantees, and failure handling — decisions that affect whether a message goes out now

Bring clarity to ambiguous technical problems — breaking undefined challenges into concrete, actionable plans

Collaborate across product, deliverability, compliance, and platform teams to expand messaging capabilities

Drive best practices in system design, code quality, and engineering process across your team

Mentor and grow engineers, contributing to a high bar across the broader Messaging Infra organization

Build smarter systems and workflows by putting AI at the center of how you and your team work

Who you are

8+ years of engineering experience building and operating online, real-time distributed systems — systems processing live events where latency and timely processing matter to the customer or downstream service, rather than primarily offline/batch pipelines where processing can be deferred and replayed without immediate customer impact

You've owned production services measured in messages/events per second, not just da