Location: United States – Remote Clearance: Ability to obtain and maintain a Public Trust LTS is seeking a Senior AI Platform and Harness Engineer to develop and maintain the infrastructure, tooling, and evaluation frameworks that power enterprise AI solutions. This role is responsible for building the AI platform and reusable "AI harnesses" that enable Large Language Models (LLMs), AI agents, Retrieval-Augmented Generation (RAG), and Generative AI applications to be securely developed, tested, evaluated, monitored, and deployed at scale. The ideal candidate has experience with AI platforms, LLMOps, software engineering, cloud-native technologies, and backend systems, along with a passion for building reliable, observable, and production-ready AI solutions. You will work closely with AI architects, software engineers, data scientists, and product teams to ensure AI solutions are scalable, secure, cost-effective, and continuously improving. What You'll Do: Design, build, and maintain enterprise AI platform capabilities supporting Large Language Models (LLMs), AI agents, RAG, and Generative AI applications. Lead data preparation, training and fine-tuning of LLMs Develop reusable AI harnesses to automate testing, prompt evaluation, model benchmarking, regression testing, and quality assurance. Build AI evaluation frameworks to measure model accuracy, retrieval quality, hallucination detection, latency, throughput, cost, and overall application performance. Implement observability and monitoring solutions for AI applications, including telemetry, tracing, logging, dashboards, and operational metrics. Build and maintain LLMOps pipelines supporting model deployment, versioning, evaluation, experimentation, rollback, and continuous improvement. Design automated workflows for prompt testing, retrieval evaluation, AI system validation, and performance benchmarking. Develop internal tools for prompt management, model experimentation, AI performance optimization, and developer
AI Evaluation Infrastructure Engineer
Role overview
Job description
It all started with an idea at Block in 2013. Initially built to take the pain out of peer-to-peer payments, Cash App has gone from a simple product with a single purpose to a dynamic ecosystem, developing unique financial products, including Afterpay/Clearpay, to provide a better way to send, spend, invest, borrow and save to our 50+ million monthly active customers. We want to redefine the world’s relationship with money to make it more relatable, instantly available, and universally accessible. Today, Cash App has thousands of employees working globally across office and remote locations, with a culture geared toward innovation, collaboration and impact. We’ve been a distributed team since day one, and many of our roles can be done remotely from the countries where Cash App operates. No matter the location, we tailor our experience to ensure our employees are creative, productive, and
…What they are looking for
Skills & requirements
Qualification
Build grader infrastructure across ground truth checks, rubrics, and LLM-as-judge approaches; Experience evaluating LLM or ML systems, or deep systems engineering experience with a strong interest in AI evaluation
Department · Engineering - Data & Data Science

Hiring company
Block
Made up of Square, Cash App, Afterpay, TIDAL, Bitkey, and Proto, Block, Inc. builds technology to increase access to the global economy.
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