Sr. Lead Software Engineer - Mobile Channels

Klaviyo•Boston, MA

1d•Hybrid

About The Position

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.

Requirements

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.
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.
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.
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.
Strong experience with AWS at scale; comfortable with Infrastructure as Code (Terraform), containerization, and modern observability stacks (metrics, logs, traces, SLI/SLO design).
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.
Exceptional communicator; can articulate complex technical concepts to engineers, product leaders, and executives, and can rally multiple teams toward sequenced, realistic improvements.
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.
Strong cross-functional partner; thrives in a hybrid team and high-autonomy environment; ships value early and iterates.

Nice To Haves

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.

Responsibilities

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.
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.
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.
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.
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.
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.
Mentor other engineers regularly, primarily experienced lead and senior engineers across SMS, RCS, and WhatsApp, and represent Mobile Channels' technical bar in senior hiring.
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.