This is a foundational role. You will be joining Yuma as one of the core engineers on a tight, high-performing team of 5. We move fast, iterate aggressively, and care deeply about product quality and user value. Over the past two years, we’ve built an impressive amount of product surface area, AI systems, and automation. Yet what lies ahead is even bigger. As we scale our platform, models, and AI agents, your work will have a direct and immediate impact on the experience of thousands of users. This role goes far beyond classical backend development. You will work across the full product lifecycle: new features, A/B tests, model integrations, AI agent pipelines, and performance optimization. If you enjoy working at the intersection of backend engineering, product iteration, and applied AI, you will thrive here. Backend Engineering: Architect, build, and scale large Ruby on Rails applications Own major systems within our Rails API, including performance, reliability, and maintainability Manage PostgreSQL at scale: schema design, indexing, performance diagnostics Maintain and optimize Redis + Sidekiq pipelines for high-throughput workloads Lead backend-heavy feature projects, from design to deployment AI / LLM Systems: Integrate, evaluate, and iterate on LLM providers and models Design systems that manage non-deterministic model outputs safely and predictably Build and own A/B tests, eval pipelines, and agentic workflows Optimize for latency, reliability, and cost across LLM-heavy features Contribute directly to prompts, agents, and AI system architecture Product & Full-Stack Contribution : Collaborate tightly with founders and engineers to define product requirements Jump into frontend (Next.js/React) when needed to ship features end-to-end Run rapid product iterations: fast feedback loops, experimentation, data-driven decisions Maintain a high bar for product quality while optimizing for speed of execution