An open source agent framework hands you the agent loop as code: full control, your infrastructure, no vendor meter. Seven are worth your time in 2026, from LangGraph to n8n. Pick by job, not by GitHub stars, and be honest with yourself about the last question on this page: does this agent even need to be a code project?

## The Quick Picks

Short answer. **LangGraph** for stateful production agents · **CrewAI** for fast multi-agent prototypes · **AG2** for research-style agent conversations · **LlamaIndex** for document agents · **OpenAI Agents SDK** for minimal abstractions · **Haystack** for pipeline RAG in production · **n8n** if you want self-hosted and low-code.

One disclosure up front: we build [TinyAgents](/content/tinyagents/index.html), a no-code agent platform, so we have a horse in the build-vs-buy race at the end. The framework reviews themselves are straight: these are good tools, we have used them, and for some jobs they are the only right answer. New to the topic? Our [guide to AI agents](/content/ai-agents/index.html) and the [agentic vs generative explainer](/content/ai-agents/agentic-ai-vs-generative-ai/index.html) cover the basics first.

## How We Judged

Three things, in order. **Best at:** the one job where this framework beats the other six. **Learning curve:** how long until a competent developer ships something real. **Watch out:** the thing that bites at month three, not day one. Star counts and adoption figures were checked against public sources in June 2026 and linked inline, so you can verify every number.

## 1. LangGraph

Best for · stateful production agents. **Stateful, production-grade agents.** Watch out: hardest to learn on this list.

LangGraph is the agent layer of the LangChain family, and it earned its reputation the slow way: it reached [1.0 in October 2025](https://blog.langchain.com/langchain-langgraph-1dot0/) after more than a year powering production agents at Uber, LinkedIn, and Klarna. The repo sits around [34,000 GitHub stars](https://github.com/langchain-ai/langgraph).

You model your agent as an explicit graph of nodes and edges. That buys you checkpointing, durable state, and first-class human-in-the-loop pauses. When a run fails at step 7 of 9, you resume at step 7, not from zero. That is exactly what audit-heavy production systems need.

The cost is the learning curve, the steepest here. You manage state shape, edges, and reducers yourself. Budget days of real learning before your first useful agent, not hours.

## 2. CrewAI

Best for · multi-agent prototypes. **Fast role-based multi-agent prototypes.** Watch out: high-level abstractions hide the loop.

CrewAI’s metaphor is a crew: you define agents as roles, a researcher, a writer, a reviewer, give each a goal, and the framework runs the handoffs. It is the fastest path from idea to a working multi-agent demo, and adoption backs that up: roughly [1.3 million monthly PyPI installs](https://dev.to/agentsindex/ag2-vs-crewai-the-complete-comparison-including-the-autogen-rebrand-explained-248l), about 13 times what AG2 pulls.

It is independent of LangChain, lean, and well documented. The trade: those friendly abstractions hide the loop. When a run goes sideways three agents deep, you get less low-level control than LangGraph gives you. Prototype here, then decide whether production needs more rope.

## 3. Microsoft AutoGen / AG2

Best for · agent-to-agent conversation. **Research-style conversational agents.** Watch out: the project forked; pick your line carefully.

AutoGen pioneered the pattern of agents that talk to each other to solve a problem. Then it became two projects. In November 2024 the original creators forked it as [AG2](https://github.com/ag2ai/ag2), keeping the conversational API alive. Microsoft rebuilt its own line and folded it, with Semantic Kernel, into the [Microsoft Agent Framework, which hit v1.0 in April 2026](https://dev.to/agentsindex/ag2-vs-crewai-the-complete-comparison-including-the-autogen-rebrand-explained-248l). The original AutoGen repo passed 54,000 stars before moving into maintenance mode.

So “use AutoGen” now means picking a line. AG2 is the research community’s favorite, with Docker-sandboxed code execution built in. If you live on Azure and want the supported long-term path, the Microsoft Agent Framework is that path. Just know which one you are betting on before you start.

## 4. LlamaIndex

Best for · document agents. **Agents that reason over your documents.** Watch out: agent layer is younger than its RAG core.

[LlamaIndex](https://github.com/run-llama/llama_index) started as the data framework for LLM apps and grew into a document-first agent framework. If the job is “answer and act across 10,000 PDFs, a SQL database, and three APIs,” its indexes and query engines are purpose-built for exactly that. Nothing else on this list treats your data as the main character.

Many production teams run LlamaIndex as the retrieval layer underneath a different orchestrator. That is a compliment and a caveat in one: the agent abstractions are improving fast, but they are younger than the data layer. Validate the agent side on your own use case before betting on it end to end.

## 5. OpenAI Agents SDK

Best for · minimal abstractions. **Minimal abstractions, quick handoffs.** Watch out: happiest inside the OpenAI stack.

OpenAI shipped the [Agents SDK in March 2025](https://www.respan.ai/articles/openai-agents-sdk-vs-swarm) as the production successor to its Swarm experiment. The whole mental model is three ideas: agents, tools, and handoffs, plus guardrails and built-in tracing. It is the smallest conceptual surface in this roundup, and you can read the core source in an afternoon.

That minimalism is the appeal, and the catch sits right next to it. The SDK is provider-agnostic on paper, but the tracing dashboard and hosted tools are built around OpenAI’s stack. Leaving later costs more than the README suggests. Great pick if you are committed to OpenAI; think twice if you are not.

## 6. Haystack

Best for · production RAG pipelines. **Pipeline-style RAG agents in production.** Watch out: smaller community than the LangChain orbit.

[Haystack](https://github.com/deepset-ai/haystack), from the team at deepset, came up through enterprise search, and in 2026 it has grown from a pure RAG framework into a [capable agent orchestration platform](https://pickaxe.co/post/top-ai-agent-frameworks). Its pipelines are explicit and serializable, which regulated industries love: you can read exactly what runs, in what order, and prove it to an auditor.

It is the quiet, sturdy choice. The trade is gravity: fewer tutorials, templates, and prebuilt integrations than the LangChain orbit, so you will write more glue yourself. Teams that pick Haystack tend to know precisely why they picked it.

## 7. n8n

Best for · self-hosted low-code. **Self-hosted, low-code agent automations.** Watch out: fair-code license, not OSI open source.

n8n is the bridge between this list and the no-code world. It is a visual workflow tool with an AI Agent node built on LangChain, [400+ integrations, and free unlimited executions if you self-host](https://github.com/n8n-io/n8n). At roughly 190,000 GitHub stars, it is the most-starred project on this page by a wide margin.

Two honest caveats. First, the “fair-code” Sustainable Use License is source-available, not OSI-approved open source, which matters if your legal team is strict about the term. Second, it is low-code, not no-code: real builds mean JSON, expressions, and debugging node payloads. For technical operators that is a fine deal. For everyone else, it is still code by another name.

## Side-by-Side Comparison

The seven frameworks in one table, checked June 2026:

| Framework | Best for | Learning curve | Watch out |
| --- | --- | --- | --- |
| 1. LangGraph | Stateful, production-grade agents | Steep | Hardest to learn on this list |
| 2. CrewAI | Fast role-based multi-agent prototypes | Gentle | High-level abstractions hide the loop |
| 3. AutoGen / AG2 | Research-style conversational agents | Moderate | The project forked; pick your line carefully |
| 4. LlamaIndex | Agents that reason over your documents | Moderate | Agent layer is younger than its RAG core |
| 5. OpenAI Agents SDK | Minimal abstractions, quick handoffs | Gentle | Happiest inside the OpenAI stack |
| 6. Haystack | Pipeline-style RAG agents in production | Moderate | Smaller community than the LangChain orbit |
| 7. n8n | Self-hosted, low-code agent automations | Gentle (visual) | Fair-code license, not OSI open source |

## Should You Build on a Framework or Buy a Platform?

Build on a framework when the agent is your product: custom UX, your infrastructure, full control of the loop. Buy a platform when the agent is internal plumbing: support triage, lead qualification, ops. The math nobody puts in the README shows that with a framework, the agent loop is the easy 20 percent. You still own model wiring, retries, evals, hosting, logging, and some kind of interface. Call it two engineer-weeks for a first internal agent if everything goes well. At a loaded cost of $75 an hour, that is $6,000 before the agent answers its first real question.

Frameworks genuinely win when that cost buys something. If the agent is your product, if you need custom behavior a platform cannot express, or if compliance demands your own infrastructure, write the code. No platform gives you LangGraph-grade control over state, and pretending otherwise would be dishonest.

For internal business agents, the trade flips. This is where we point at our own product, plainly disclosed: [TinyAgents](/content/tinyagents/index.html) is ours. You upload knowledge files, write rules in plain English, pick from 7 LLM providers, and set guardrails. The agent reads and writes [TinyTables](/content/tinytables/index.html), gets triggered by a form, and sends through TinyEmails, with embed modes for your site.

## Frequently Asked Questions

What is the best open source AI agent framework in 2026?

There is no single best, because they optimize for different jobs. LangGraph is the strongest pick for production agents that need state, retries, and human approval steps. CrewAI is the fastest way to prototype role-based multi-agent systems, LlamaIndex leads for document-heavy agents, and the OpenAI Agents SDK is the lightest to learn.

Are open source AI agent frameworks really free?

The license is free, but the total cost is not. You pay for LLM API calls, hosting, observability, and most of all engineering time to build and maintain the loop around the framework.

Should I use LangChain or LangGraph for AI agents?

Start with LangChain's agent abstractions, then drop down to LangGraph when you need explicit control over state, branching, and human-in-the-loop steps.

What happened to Microsoft AutoGen?

AutoGen split in November 2024. AG2 is the community fork run by AutoGen's original creators, and it keeps the conversational API going.

Should I use an open source AI agent framework or a no-code platform?

Build on a framework when the agent is your product or must run on your own infrastructure, since nothing matches code for control. A framework build takes engineer-weeks before the first useful answer; a no-code platform like TinyAgents ships the same internal agent in an afternoon for $49 a month flat.