Seeking a curious and AI-forward Senior Fullstack SDK Engineer to work remotely in a full-time capacity, responsible for building and evolving Customer.io's SDKs across platforms, leading SDK initiatives end to end, and improving SDK delivery infrastructure. Key responsibilities Build and evolve Customer.io's SDKs across platforms, including Android, iOS, Node, and Go Lead SDK initiatives by setting technical direction, writing code, managing releases, and owning outcomes Enhance SDK delivery infrastructure to ensure reliable and low-friction shipping processes Required qualifications Expert-level competency in at least one established programming language with strong software and API design fundamentals Experience building and evolving mature, production-quality software with an understanding of system integration Exceptional fluency with current LLMs and agentic coding tools for navigating unfamiliar codebases High autonomy in ambiguous environments, capable of clarifying problems and driving implementation independently Ability to work effectively across multiple languages and stacks, though prior experience in all supported languages is not required