Guide, updated Oct 16, 2026
Best AI agent frameworks
Libraries for building agents and multi-agent workflows. We list 6 agent frameworks, 6 open source. Summaries come from each vendor's own site and every link was checked on or before Oct 16, 2026.
Shortlist
All 6 at a glance
Alphabetical. Nothing in this guide is a paid placement.
| Tool | What it does | Open source | More |
|---|---|---|---|
| CrewAI | Framework and platform for multi-agent teams. | Yes | Alternatives |
| LangGraph | Agent orchestration framework with durable execution and human-in-the-loop. | Yes | Alternatives |
| Mastra | TypeScript framework for agents with memory, tools, MCP, and workflows. | Yes | Alternatives |
| OpenAI Agents SDK | OpenAI's lightweight Python framework for multi-agent workflows. | Yes | Alternatives |
| Pydantic AI | Type-safe Python agent framework from the Pydantic team. | Yes | Alternatives |
| Vercel AI SDK | Unified TypeScript SDK for AI apps and agents across model providers. | Yes | Alternatives |
How to choose
What to check before you pick
- Language: TypeScript or Python first.
- Model support: one provider or many.
- Building blocks: tools, memory, workflows, multi-agent support, human-in-the-loop.
- Durability: can long-running agents survive restarts?
- License and hosted options for production.
This checklist is general advice. Check each vendor's docs and pricing page for current details.
The tools
Each option in one paragraph
CrewAI
crewai.comFramework and platform for multi-agent teams.
In their words: “CrewAI”
LangGraph
langchain.comAgent orchestration framework with durable execution and human-in-the-loop.
In their words: “LangGraph: Agent Orchestration Framework for Reliable AI Agents”
Mastra
mastra.aiTypeScript framework for agents with memory, tools, MCP, and workflows.
In their words: “TypeScript AI Framework for Agents and Apps | Mastra”
OpenAI Agents SDK
openai.github.ioOpenAI's lightweight Python framework for multi-agent workflows.
In their words: “OpenAI Agents SDK”
Pydantic AI
pydantic.devType-safe Python agent framework from the Pydantic team.
In their words: “Pydantic AI | Pydantic Docs”
Vercel AI SDK
ai-sdk.devUnified TypeScript SDK for AI apps and agents across model providers.
In their words: “AI SDK”
Head to head
Compare them side by side
FAQ
Questions
Which agent frameworks does Agent Stack Directory list?
6: CrewAI, LangGraph, Mastra, OpenAI Agents SDK, Pydantic AI, Vercel AI SDK.
Which of them are open source?
CrewAI, LangGraph, Mastra, OpenAI Agents SDK, Pydantic AI, Vercel AI SDK are marked open source in our data.
How is this list ordered?
Alphabetically. No placement in this guide is paid. Sponsored and featured tools are labeled elsewhere on the site and never reordered here.
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