Senior Fullstack SDK Engineer

Stack

Responsibilities

• ▹Build and evolve Customer.io's SDKs across platforms (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
• ▹Partner 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
• ▹Understand what the engineers integrating with the SDKs need, and occasionally engage with them directly

Requirements

• ▹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
• ▹Exceptional fluency with current LLMs and agentic coding tools (e.g. Claude, Cursor, Codex)
• ▹High autonomy in ambiguous environments: clarify the problem, validate its value and drive implementation without close direction
• ▹Strong written and verbal communication, able to explain technical decisions and tradeoffs clearly
• ▹Ability to work across multiple languages and stacks; prior experience in every supported language (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
• ▹Forward-deployed engineering experience

Soft skills

What we offer

• ▹Starting salary $150,000 - $200,000 USD (or equivalent in local currency) depending on experience
• ▹100% coverage of medical, dental, vision, mental health and supplemental insurance premiums for you and your family
• ▹16 weeks paid parental leave
• ▹Unlimited PTO
• ▹Stipends for remote work and wellness
• ▹Professional development budget

About the company

Over 9,000 companies use the Customer.io platform to send billions of emails, push notifications, in-app messages and SMS every day, driven by real-time behavioral data. Under the hood it runs on Go, React, Ember and AI.