Senior Fullstack SDK Engineer

About the role

We are seeking a skilled Fullstack SDK Engineer to join our team. You will be instrumental in developing and enhancing the software development kits that developers use to integrate with our platform. This role involves taking ownership of projects from conception to completion, focusing on creating excellent developer experiences.

Key facts

What you'll do

Develop and enhance Customer.io's SDKs across various platforms, including Android, iOS, Node, and Go, alongside supporting developer tools.

Lead SDK development initiatives, defining technical direction, writing code, managing releases, and ensuring successful outcomes.

Improve the infrastructure for SDK delivery, encompassing continuous integration, automated testing, version management, and publishing processes for reliable and efficient releases.

Collaborate with product and design teams to translate broad objectives into intuitive developer experiences.

Utilize AI agents for complex code modifications across different codebases and languages by defining tasks, crafting prompts, and validating results.

Apply a deep understanding of customer needs to ensure the SDKs meet the requirements of engineers integrating with our services, potentially engaging directly with them.

Requirements

Demonstrated expert-level proficiency in at least one established programming language, with a solid foundation in software design and API design principles.

Proven experience in building and maintaining production-quality software, with a clear understanding of system architecture and how external developers interact with them.

Exceptional fluency in current large language models and agentic coding tools, such as Claude, Cursor, or Codex, for tasks like understanding unfamiliar code, working across languages, and automating processes.

High degree of autonomy in ambiguous situations, capable of clarifying problems, assessing their value, and driving implementation without constant supervision.

Strong written and verbal communication skills, able to articulate technical decisions and trade-offs clearly.

Ability to work effectively across multiple programming languages and technology stacks. Prior experience with Swift, Kotlin, Node, and Go is not mandatory.

Nice to have

Experience building external-facing SDKs, APIs, or developer tools.

Experience managing continuous integration, testing, versioning, or release infrastructure.

Experience in forward-deployed engineering roles.

Skills & tools

Go, React, Ember, Node.js, Swift, Kotlin, Claude, Cursor, Codex

Practical notes

Starting salary range: $150,000 - $200,000 USD per year, adjusted for experience and market rates.

Benefits include 100% coverage for medical, dental, vision, mental health, and supplemental insurance premiums for employees and their families.

Additional benefits include 16 weeks of paid parental leave, unlimited paid time off, stipends for remote work and wellness, and a professional development budget.

Interviews will be conducted via Zoom. Offers will be provided in writing on official Customer.io letterhead.

Customer.io is committed to fostering inclusion and equity within the tech industry.

About the company

Customer.io is a technology company that builds communication platforms for customer engagement. The business focuses on helping organizations deliver timely and relevant messages across channels such as email, push notifications, and SMS. Its tools allow teams to automate outreach based on real-time user behavior and data signals. This approach supports strategies that aim to increase retention and strengthen relationships with end users. The company operates in a sector where service quality often determines competitive position. Effective communication depends on the ability to adapt tone and timing to the needs of each recipient. Customer.io provides the infrastructure to manage this complexity at scale. Clients use the platform to design workflows that reflect their specific service standards and brand values. As the industry evolves, automation and artificial intelligence are reshaping how support and marketing teams operate. AI-driven chatbots and predictive logic are becoming standard components of modern engagement stacks. These technologies promise higher productivity and more consistent experiences. Customer.io integrates these capabilities so businesses can combine human oversight with machine efficiency. The platform serves companies that view customer communication as a core asset rather than a cost center. By unifying data and delivery, the system helps teams execute cohesive service packages. The goal is to enable interactions that feel personal and intentional at every touchpoint.