The Vercel AI SDK is a TypeScript toolkit for building AI applications and agents. It is Apache-2.0 and is the TypeScript-native pick among the vendor SDKs, widely used in web-app contexts. Its design centers on a unified provider API: you swap models by swapping a provider package, with no house model of its own. Multi-agent work is expressed through subagents, separate agent instances a main agent can spawn for focused subtasks. MCP support is native through a built-in client, though that client is a lightweight tool-conversion client rather than a full MCP implementation (it does not cover session management or resumable streams). The toolkit reached version 6, generally available since December 2025. For open-source AI the relevant point is that it is fully open (Apache-2.0) and genuinely model-neutral: there is no Vercel model, so the provider choice is the developer's. Mastra is built on top of it, which is why the two share a TypeScript, model-routing lineage.
The Stack · Agents · Open source
Vercel AI SDK
Vercel's TypeScript AI toolkit; Apache-2.0, model-agnostic via a unified provider API, subagents, native MCP. AI SDK 6 GA December 2025.
Sources
- Vercel AI SDK agents documentation https://ai-sdk.dev/docs/agents/overview
- vercel/ai LICENSE (Apache 2.0) https://raw.githubusercontent.com/vercel/ai/main/LICENSE
- Vercel AI SDK MCP tools docs https://ai-sdk.dev/docs/ai-sdk-core/mcp-tools
- Vercel AI SDK subagents docs https://ai-sdk.dev/docs/agents/subagents
- AI SDK 6 announcement (2025-12-22) https://vercel.com/blog/ai-sdk-6
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