Senior Fullstack SDK Engineer

What You’ll Do

• 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

What we're looking for

• 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
• Forward-deployed engineering experience

Compensation & Benefits

Starting salary for this role is $150,000 - $200,000 USD (or equivalent in local currency) depending on experience and subject to market rate adjustment.

We offer 100% coverage of medical, dental, vision, mental health, and supplemental insurance premiums for you and your family. We also offer 16 weeks paid parental leave, unlimited PTO, stipends for remote work and wellness, a professional development budget, and more.