Vercel AI SDK Complete Guide — One Unified API for OpenAI, Anthropic, and Gemini
You shipped on the OpenAI API and now want to try Claude and Gemini — and you've burned two hours rewriting against three different SDKs. The Vercel AI SDK (just "AI SDK" since 2026) collapses that into "one import, one function, every provider," with 20M+ monthly downloads and AI SDK 6 shipping Agents, MCP, tool approval, and DevTools — the de facto standard for unified LLM interfaces in 2026. This article covers what the AI SDK is, three practical reasons to use it (free switching, 1/3 the implementation, type safety), a 5-minute quickstart from generateText to streamText, type-safe structured output via generateObject and Zod, tool calling and agent loops, a 10-line React chat UI with useChat, switching between Claude/GPT/Gemini in 3 lines, and the three production pitfalls (provider feature gaps, stream-abort billing, type-inference overload) — all with working code grounded in AI SDK 6 as of May 2026.