Vercel AI SDK is a free, open-source TypeScript library for building AI-powered web applications. Created by the makers of Next.js, it has become the leading AI development toolkit with over 20 million monthly npm downloads. The SDK provides a unified provider API that lets developers switch between AI providers like OpenAI, Anthropic, Google, and more by changing just one line of code. AI SDK 6, released in December 2025, introduced agent abstractions, tool execution approval for human-in-the-loop workflows, built-in DevTools, full MCP (Model Context Protocol) support, reranking, image editing, and video generation capabilities. The SDK supports streaming responses via Server-Sent Events, type-safe object generation with structured JSON outputs, and multi-turn tool execution with automatic error recovery. It works across major frameworks including React, Next.js, Vue, Nuxt, SvelteKit, and Node.js. Key capabilities include generative UI for dynamic AI-powered interfaces, speech and audio APIs, agentic loop control for fine-tuning multi-step tool calls, and robust stream parsing with built-in healing mechanisms.