How Stripe built Kai on Deep Agents in one week

Stripe built Kai, its company-wide Knowledge AI Platform, on LangChain's open-source Deep Agents harness, with one engineer shipping the initial version in a single week. The stack layers a Stripe-specific harness and configuration layer over Deep Agents, using filesystem middleware backed by S3, sandbox middleware for code execution, summarization middleware for long sessions, and skill-based dynamic tool loading across 500+ internal MCP tools and 1,000+ skills. Kai grew from 296 to over 5,000 users in roughly four weeks and is now used weekly by 83% of Stripe across more than 60k sessions.