Senior Fullstack SDK Engineer

Hi, I’m Josh, Engineering Manager at Customer.io. We’re looking for a curious, AI-forward Fullstack SDK Engineer to join our SDK team and help us build the tools that developers rely on to integrate with Customer.io.

Over 9,000 companies - from scrappy startups to global brands - use our platform to send billions of emails, push notifications, in-app messages, and SMS every day. Customer.io powers automated communication that people actually want to receive.

We help teams send smarter, more relevant messages using real-time behavioral data. Under the hood: Go, React, Ember and AI help us ship fast and scale with confidence.

Build and evolve Customer.io's SDKs across platforms - including Android, iOS, Node, and Go - and the developer tools that support them
Lead SDK initiatives end to end: set technical direction, write the code, manage the release, and own the outcome
Improve SDK delivery infrastructure - CI, automated testing, versioning, publishing, and release processes - so shipping is reliable and low-friction
Partner closely with product and design to turn loosely defined goals into a great developer experience
Use AI agents to make multi-file changes across unfamiliar codebases and languages by scoping the work, writing the prompt, and verifying the output
Bring strong customer empathy to the role - understanding what the engineers integrating with our SDKs actually need, and occasionally engaging directly with them

Expert-level competency in at least one established programming language, with strong software design and API design fundamentals
Experience building and evolving mature, production-quality software, with a clear understanding of how systems fit together and how other developers consume them
Exceptional fluency with current LLMs and agentic coding tools (e.g., Claude, Cursor, Codex) - using AI to understand unfamiliar codebases, work across languages, and run things in parallel or autonomously
High autonomy in ambiguous environments - you clarify the problem, validate its value, and drive implementation without close direction
Strong written and verbal communication, with the ability to explain technical decisions and tradeoffs clearly
Ability to work effectively across multiple languages and stacks; prior experience in every language we support (Swift, Kotlin, Node, Go) is not required

Nice to have: experience building external-facing SDKs, APIs, or developer tools; experience owning CI, testing, versioning, or release infrastructure; or forward-deployed engineering experience.