Built by Agents: How Leading YC Companies are Building AI in Production

Every AI demo looks impressive. Building AI that works reliably in production is a different story. Hear from YC founders at Runtime, 21st, Paper Instruments, Replicas, and Lark share the technical decisions, tradeoffs, and hard-won lessons behind the products they're building. Agenda 6:00: Doors open. Tapas & sushi, drinks, mingling 6:30 - 7:30: Five YC founders share how they're building on the agentic stack Runtime lets non-engineering teams build and run cloud agents without managing the infrastructure.Paper Instruments post-trains LLMs to accelerate knowledge work.Lark is an AI testing platform that helps engineering teams catch product issues faster with self-healing end-to-end tests.21st is a marketplace for browsing and publishing crafted React UI components, themes, and templates that developers can drop into their projects.Replicas is a background coding agent that turn tickets into PRs. 7:30 - 8:00: More networking About E2B​E2B gives AI agents computers with real-world tools. Fast, secure, and built for scale, it powers the infrastructure behind Manus, Genspark, Lindy, and over 120 YC companies.