I Evaluated Every AI Chat UI Library in 2026. Here's What I Found (and What I Built)

The author evaluated major AI chat UI libraries in 2026, identifying assistant-ui as best for React teams, CopilotKit for full agent frameworks, Deep Chat for quick prototypes or non-React stacks, and Chainlit for Python backends. The review highlights four types of lock-in (framework, architecture, ecosystem, API-surface) as the key insight, and details the surprisingly broad scope of building production chat UIs—streaming, accessibility, trust layers, and theming—that justifies using these libraries over building from scratch.