Senior AI Engineer (Node.js, LLM)

TL;DR

Senior AI Engineer (Node.js, LLM): Building and optimizing AI infrastructure for production-ready LLM experiences with an accent on advanced prompt systems, structured outputs, and complex LLM workflows. Focus on observability, debugging, evaluation, and data-driven decisions for model performance, reliability, and cost using tools like Langfuse and OpenRouter.

Location: Remote. Applicants from any country are welcome, provided they are located within approximately ± 4 hours of CET.

Company

hirify.global is a leading tech company creating innovative consumer products across health, education, and entertainment industries.

What you will do

• Design complex, dynamic prompt templates with conditional logic and efficiently reuse information and context within prompts to maximize generation quality and reasoning.
• Implement various response schemes (JSON mode, function calling, Zod/JSON schemas) to ensure AI outputs are predictable and ready for seamless integration into application logic.
• Build robust evaluation pipelines and use Langfuse to collect feedback and score the quality of responses in real time.
• Perform deep debugging of complex LLM chains using Langfuse traces to identify bottlenecks and optimize for cost, latency, and context window usage.
• Run systematic experiments across different models via OpenRouter (e.g., comparing Claude 3.5 Sonnet vs. GPT-4o) and analyze results based on quantitative metrics.
• Make deployment decisions for new prompts or models strictly based on quantitative benchmarks and trace data, rather than intuition.

Requirements

• Deep knowledge of Node.js & Next.js stack to build reliable services and handle complex LLM-generated data.
• Proven experience in building prompts where content is highly dependent on input variables and context injection.
• Experience working with unified APIs like OpenRouter, managing rate limits, and selecting the most cost-effective models for specific tasks.
• Understanding of LLM observability principles — setting up tracing, creating test datasets, and integrating scoring systems using Langfuse (or similar).
• Experience with evaluation frameworks like RAGAS or building custom “LLM-as-a-judge” systems.
• Ability to transform raw generation logs into actionable business metrics and technical insights with an analytical mindset.

Nice to have

• Practical experience in fine-tuning models for specific domain tasks or JSON compliance.
• Understanding how to build and optimize Retrieval-Augmented Generation (RAG) systems, including indexing, retrieval, and re-ranking.
• Basic knowledge of Python for working with data science scripts or AI evaluation libraries.

Culture & Benefits

• Embrace the freedom of a remote work environment, promoting a healthy work-life balance.
• Enjoy unlimited paid time off to recharge and prioritize your well-being.
• Celebrate and relax on national holidays with paid time off.
• Experience seamless productivity with top-notch Apple MacBooks provided to all employees who need them.
• Unlock the benefits of flexibility, autonomy, and entrepreneurial opportunities with a flexible Independent Contractor Agreement.

Hiring process

• Recruiter Screening (40 minutes).
• Technical Interview (60 minutes).
• Final Interview (30 minutes).