The Vercel AI SDK is the default choice for a lot of JavaScript and TypeScript developers building an AI feature into a web app, mainly because it treats streaming, React integration, and provider abstraction as first-class concerns rather than things bolted on after the fact. A single unified API lets a developer switch between OpenAI, Anthropic, Google, and other providers with minimal code changes, which matters when model pricing and capability keep shifting.
Its React hooks handle the tricky parts of streaming a model's response into a UI in real time, including the UI-state bookkeeping that building this by hand from scratch is genuinely annoying to get right. Newer versions added agent-building primitives, including tool calling and multi-step agent loops, extending it beyond simple chat UIs into the same general territory as LangChain, though with a narrower, more web-framework-specific focus.
It's free and open source, maintained by Vercel, and its tight integration with Next.js has made it something close to a default for TypeScript-first teams building AI features, in the same way v0 has become a default for generating UI in that same ecosystem.