Senior AI Software Engineer

Ruby Labs Ltd.

Job Overview

Location

European Union

Job Type

Full-time

Full Job Description

📋 Description

• Own end-to-end delivery of major AI engineering features, ensuring timely and high-quality production deployment.
• Ensure consistent output structure, formatting, and predictability across all user-facing AI interactions, regardless of underlying LLM provider.
• Design and maintain output-type-based AI systems including segmentation, routing, and enforcement logic for LLM responses.
• Integrate and orchestrate multiple LLM providers via OpenRouter, managing model selection, fallback strategies, and cost optimization.
• Build and orchestrate agentic, tool-using AI workflows using MCP-based tool contracts, function-calling interfaces, and reliable AI-to-service integrations.
• Develop complex, multi-step LLM workflows using orchestration frameworks such as LangChain or LlamaIndex for advanced reasoning, context reuse, and retrieval.
• Design and manage production prompt systems with dynamic prompting, context injection, and conditional logic.
• Own deployment and release of LLM experiments, prompt management, and Langfuse-based evaluation pipelines.
• Run A/B tests across LLM models, analyze results, and present data-driven impact assessments of AI features and experiments.
• Monitor AI system metrics including quality signals, latency, and release health using Langfuse and other observability tools.
• Deep-debug complex LLM chains using Langfuse traces to identify bottlenecks and optimize for cost, latency, and context-window usage.
• Build output-scoring systems to root-cause hallucinations, logic errors, and structural deviations in AI outputs.
• Write clean, scalable, and maintainable TypeScript code across Next.js and Node.js stacks.
• Develop reliable backend logic for AI systems with strong error handling, request validation, fallback flows, and predictable production behavior.
• Ensure high code quality through testing, code reviews, and adherence to clear engineering standards.
• Monitor, troubleshoot, and improve production performance, reliability, and system health of AI infrastructure.
• Drive maintainability and technical quality through solid architecture, refactoring, and disciplined release practices.
• Collaborate closely with product, growth, data, and billing teams within a squad-based engineering structure.
• Operate as a senior technical voice within the AI engineering squad, setting standards and mentoring peers on AI system design.

🎯 Requirements

• 6+ years of backend/full-stack software engineering experience with production-grade TypeScript/Node.js
• 2+ years of hands-on experience building AI/LLM systems in production
• Deep experience working with LLM APIs (OpenAI, Anthropic, or similar) in production environments
• Experience with agentic AI, tool-based workflows (function calling/tool execution), and/or RAG pipelines
• Experience with LLM observability tools such as Langfuse, LangSmith, or equivalent
• Solid understanding of Redis and relational databases such as PostgreSQL

🏖️ Benefits

• Remote Work Environment: Work from anywhere with flexibility in schedule
• Unlimited PTO: Unlimited paid time off to recharge and prioritize well-being
• Paid National Holidays: Paid time off for recognized national holidays
• Company-provided MacBook: Top-tier Apple MacBook provided for all employees who need one
• Flexible Independent Contractor Agreement: Access to tax advantages, autonomy, and entrepreneurial freedom with reduced employment obligations
• Work within CET (±4 hours) time zone for optimal collaboration

Skills & Technologies

Python

JavaScript

TypeScript

Ruby

Senior

Remote

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Ruby Labs Ltd.

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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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