Job Overview
Location
European Union
Job Type
Full-time
Category
Software Engineering
Date Posted
May 3, 2026
Full Job Description
đź“‹ Description
- • As a Senior AI Engineer at Ruby Labs Ltd., you will shape the company's AI infrastructure and drive production-ready LLM experiences, playing a critical role in advancing consumer-led products across health, education, and entertainment industries.
- • Your day-to-day responsibilities include designing advanced prompt engineering systems, implementing structured outputs and schemas, building evaluation pipelines with Langfuse, performing deep debugging of LLM chains, conducting AI A/B testing via OpenRouter, making data-driven deployment decisions, developing output scoring systems, and regularly re-evaluating and fine-tuning models for optimal performance.
- • Ruby Labs is a leading tech company creating innovative consumer products with a mission to drive the future of consumer-led solutions, offering a dynamic, fast-paced environment where ambition and impact are highly valued.
- • In this role, you will gain deep expertise in LLM observability, prompt engineering at scale, model evaluation and optimization, and production AI systems—positioning you as a specialist in reliable, cost-effective LLM integration within modern TypeScript/Node.js stacks.
🎯 Requirements
- • Deep knowledge of Node.js & Next.js to build reliable services and handle complex LLM-generated data
- • Proven experience in building dynamic prompts with content highly dependent on input variables and context injection
- • Experience working with OpenRouter, including managing rate limits and selecting cost-effective models for specific tasks
- • Understanding of LLM observability principles, including setting up tracing, creating test datasets, and integrating scoring systems using Langfuse or similar tools
- • Experience with evaluation methodologies such as RAGAS or building custom 'LLM-as-a-judge' systems
- • Ability to transform raw generation logs into actionable business metrics and technical insights
🏖️ Benefits
- • Remote Work Environment: freedom to work from anywhere, anytime, promoting a healthy work-life balance
- • Unlimited PTO: enjoy unlimited paid time off to recharge and prioritize well-being
- • Paid National Holidays: celebrate and relax on national holidays with paid time off
- • Company-provided MacBook: top-notch Apple MacBooks provided to all employees who need them
- • Flexible Independent Contractor Agreement: offers flexibility, autonomy, tax advantages, and entrepreneurial opportunities
Skills & Technologies
About Ruby Labs Ltd.
Ruby Labs Ltd. is a London-based product studio that builds and scales consumer subscription mobile and web applications. The company focuses on health, wellness, and productivity verticals, developing apps such as Hint, Able, and the award-winning fitness platform FitCoach. Using data-driven growth and proprietary technology, Ruby Labs rapidly prototypes, launches, and iterates products to serve millions of global users. The team combines engineering, product design, and performance marketing expertise to create sustainable digital businesses. Founded in 2018, Ruby Labs operates a portfolio of self-funded apps, emphasizing user privacy, scientific validation, and long-term customer value.
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