# Open-Source AI Agent Frameworks

> Source: https://theagentsindex.com/collections/open-source-ai-agent-frameworks (curated, quality-gated, re-verified)
> Curated by: The Agents Index Editorial, Research desk

12 of the 14 agent frameworks in our index carry a clean, unrestricted open-source license on the code you would actually run. No source-available carve-out. No separate commercial license required to get the controls a production team needs while self-hosting. A framework is not a product you sign into; it is code that lands in your own repository, so the license attached to it matters more here than it does for a hosted agent.

Two of the 14 do not clear that bar, and both are open at the core. Mastra's framework is Apache-2.0 and free to self-host, but the RBAC, SSO and IAM controls a production team needs sit behind a separate Enterprise Self-Hosted tier, billed as a flat annual fee on top of the open code. Claude Agent SDK's Python and TypeScript wrapper packages carry an MIT license, but Anthropic's own docs state that using the SDK as a whole is governed by its commercial Terms of Service, so the license on the wrapper does not cover what you are actually agreeing to when you run it.

This is not the same list as our [open-source AI agent tools collection](/collections/open-source-ai-agent-tools/), which spans coding agents, voice agents and agent platforms too, not just the tools you build an agent with (every entry here also appears there). It is also not the same as our [ranking of all 14 frameworks](/best-ai-agent-frameworks/), which scores the full set on capability and includes Mastra and Claude Agent SDK alongside the 12 open ones here.

Among these 12: LangChain remains the largest and most integration-heavy framework in the group; Microsoft ships two that clear this bar, AutoGen and its newer successor, Agent Framework; and AgentsKit is the newest and least proven, four months old with an MIT core and its hosted layer, AgentsKit OS, still enterprise-only early access. Every one of them lets you point the framework at any model provider you choose and keep running if the vendor ever disappears, a guarantee a closed SDK cannot make.

| Name | What it is | Why it's here | Pricing | API |
| --- | --- | --- | --- | --- |
| [LangChain](https://theagentsindex.com/langchain.md) | The most widely-used framework for building LLM apps and agents, with LangGraph for stateful multi-agent control: open-source and free to self-host. | The most widely adopted agent framework here; MIT-licensed core, free to self-host with no vendor lock-in. | — | Yes |
| [CrewAI](https://theagentsindex.com/crewai.md) | Open-source Python framework for role-based multi-agent crews, with a hosted build and runtime that adds enterprise governance, native SDKs for the major LLMs, and Ollama via LiteLLM. | MIT-licensed multi-agent orchestration framework, reached a stable 1.0 general-availability release in October 2025. | — | Yes |
| [Microsoft AutoGen](https://theagentsindex.com/microsoft-autogen.md) | Microsoft's open-source framework for orchestrating conversations between multiple AI agents. Now in maintenance mode. | Microsoft's MIT-licensed multi-agent framework, now frozen in favor of its own successor below; free to self-host, pay only your own model provider. | — | — |
| [Microsoft Agent Framework](https://theagentsindex.com/microsoft-agent-framework.md) | Microsoft's unified, MIT-licensed agent SDK for .NET and Python: the supported successor to AutoGen and Semantic Kernel. | Microsoft's MIT-licensed successor to AutoGen and Semantic Kernel, free to self-host across .NET, Python and Go, or an optional Azure-billed managed layer on top. | — | Yes |
| [LlamaIndex](https://theagentsindex.com/llamaindex.md) | Open-source data framework for LLM apps, with LlamaParse as the paid agentic OCR for messy documents and LlamaAgents for document workflows. | MIT-licensed core framework for building agents over your own data; the paid LlamaCloud parsing layer is optional. | — | Yes |
| [LangGraph](https://theagentsindex.com/langgraph.md) | Open-source, MIT-licensed framework for building stateful, multi-agent AI workflows on cyclical graphs. | MIT-licensed agent runtime from the LangChain team, free to self-host; LangSmith and LangGraph Platform are optional hosted layers on top, not a gate on the library itself. | — | Yes |
| [Google Agent Development Kit](https://theagentsindex.com/google-adk.md) | Google's open-source, code-first agent SDK with five language runtimes (Python, TypeScript, Go, Java, Kotlin), native A2A and MCP support, and an optional managed runtime on Google Cloud. | Apache-2.0 licensed across all four of its language SDKs (Python, Go, Java, TypeScript); Google's own official framework, free to self-host anywhere. | — | Yes |
| [OpenAI Agents SDK](https://theagentsindex.com/openai-agents-sdk.md) | OpenAI's lightweight open-source framework for building agents in Python and TypeScript, with handoffs, guardrails, tracing and a sandboxed workspace mode for long-running work. | MIT-licensed and free to self-host, OpenAI's own lightweight SDK for building agentic workflows. | — | Yes |
| [Pydantic AI](https://theagentsindex.com/pydantic-ai.md) | The Python AI SDK for type-safe agents, realtime voice, image generation and embeddings, with every model a string swap away. | MIT-licensed, type-safe Python framework from the team behind Pydantic; free to run anywhere. | — | — |
| [Letta](https://theagentsindex.com/letta.md) | Letta is the open-source framework behind Letta Code, a stateful coding agent whose memory, skills, and identity persist across sessions rather than rebuilding context on every call. | Apache-2.0 licensed framework with persistent memory; self-host free or opt into managed Letta Cloud later. | — | Yes |
| [Agno](https://theagentsindex.com/agno.md) | An Apache 2.0 Python agent SDK and AgentOS runtime, with a Control Plane you run in your own cloud. | Apache-2.0 licensed Python framework, formerly Phidata, with built-in memory, knowledge and multi-agent Teams; the paid AgentOS runtime is a separate BYOC product, not a gate on the framework itself. | — | Yes |
| [AgentsKit](https://theagentsindex.com/agentskit.md) | Open-source, MIT-licensed JS/TS toolkit for building AI agents with a 10KB zero-dependency core and 50 built-in integrations. | MIT-licensed TypeScript foundation for building agents, with the newest and least proven track record here; AgentsKit OS, a separate hosted layer, remains enterprise-only early access, but the open-source core is the only way most teams will run it. | — | Yes |

## How this list is built

A framework earns a place here only if it belongs to this site's frameworks category and its entire self-hostable codebase carries a clean, unrestricted OSI-style license: MIT, Apache-2.0, GPL-3.0-or-later or AGPLv3, with no source-available carve-out and no separate commercial license gating the controls a production deployment needs. This is the same bar our open-source AI agent tools collection applies, narrowed to one category. Verified against each framework's own listing research (license type, pricing tiers and FAQ text), not a vendor's marketing claim of "open source."