Flex is a South Korea-based startup offering an AI-powered, all-in-one SaaS platform for HR and finance operations.
<div class="content-intro"><p>Flex is a growth-stage, NYC headquartered FinTech company that is creating the best rent payment experience. It’s hard to believe that it’s 2026 and paying rent on time is expensive, inflexible, and difficult. We’re here to change that! Flex enables our users to pay rent throughout the month on a schedule that better fits their finances and budget. Our mission is to empower as many renters as possible with flexibility over their most significant recurring expense. After deliberately keeping a stealth profile as we built up unprecedented investor support and an enthusiastic user base, we are looking for motivated individuals to help us keep our mission growing. Will you be a part of the team?</p></div><h1><span style="font-size: 12pt;"><strong>About the role</strong></span></h1> <p><span style="font-size: 10pt;">Flex is looking for a Staff AI Engineer to join our AI Central Team and help us transform the way we work by building the tools and capabilities that support AI-first workflows across Flex.</span></p> <p><span style="font-size: 10pt;">As a Staff AI Engineer at Flex, you’ll help set technical direction and shape the long-term architecture of the AI systems and tools that all departments use to power their agentic workflows. You will own AI platform features and capabilities end-to-end including analysis, planning, implementation and production rollout to our internal customers. You’ll work closely with your AI Central Team peers and consult with department leads to anticipate business needs and proactively build the AI capabilities to address them. You’ll also play a critical role in mentoring, elevating technical standards, and ensuring the success of our Flex’s transformation into an AI-first organization.</span></p> <p><span style="font-size: 12pt;"><strong>What you’ll do</strong></span></p> <ul> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Design, implement, and maintain the agent platform including orchestration, tool execution, sandboxed code runtimes, observability, and the developer-facing SDKs and UI.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Design and develop new APIs, SDKs, and developer surfaces that let other teams onboard agents quickly and safely, with strong defaults for evals, guardrails, human-in-the-loop review, and audit.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Scale the platform to support a growing catalog of agents, skills, and MCP integrations across Flex while maintaining performance, reliability, and cost efficiency.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Continuously improve our daily operations with automation, tooling, design evolution, and observability, including agent-trace visibility, evaluation pipelines, and sandbox runtime monitoring.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Work closely with cross-functional teams to identify high-leverage AI use cases and turn them into production-ready agents on the platform.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Set the bar for AI-assisted engineering practices and responsible AI use across Flex, mentor engineers on how to design, build, and operate agentic systems, and bring outside innovation back into our roadmap.</span></li> </ul> <h1><span style="font-size: 12pt;"><strong>Key qualifications</strong></span></h1> <p><span style="font-size: 10pt;"><strong><span style="font-size: 12pt;">Skills that are required:</span> </strong></span></p> <ul> <li style="font-size: 10pt;"><span style="font-size: 10pt;">6+ years of experience in software development or a related field, with at least 2+ years building production AI or agentic systems.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Experience in technical leadership, guiding engineering teams through complex projects.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Hands-on experience with coding CLIs and AI dev tools (Claude Code, Codex, OpenCode, Cursor, or equivalents) - both as a daily-driver user and as a builder integrating them into team workflows.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Experience with agent infrastructure and code-execution sandboxes (Modal, E2B, Cloudflare Sandboxes, Daytona, or Firecracker/gVisor-based runtimes), with a clear point of view on isolation, scaling, and cost trade-offs.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Experience building AI-first workflows end-to-end, including LLM application design, prompt and context engineering, RAG, and human-in-the-loop patterns.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Experience creating and managing agents and agent platforms, including multi-agent orchestration (LangGraph, custom planners, sub-agent patterns), tool/skill registries, and MCP-based integrations.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Experience with eval frameworks and offline/online evaluation of agent quality, plus observability and tracing for non-deterministic systems.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Experience with Java, Python, Golang, or TypeScript/Node.js.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Strong experience with relational SQL and NoSQL databases, such as MySQL/PostgreSQL/DynamoDB.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Experience designing and developing fault-tolerant and scalable distributed systems, including workflow and job-orchestration engines.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Experience with AWS cloud services: ECS/EKS, Lambda, API Gateway, VPC, RDS, etc.</span></li> <li style="font-size: 10pt;"><span style="font-size: 10pt;">Infrastructure as code (AWS CLI, AWS CDK/Terr