Harness is one of the hottest topics in the agent world right now. Most models are good enough these days; what really sets agents apart is the layer wrapped around the model.
Setting vendors’ own harnesses aside, the open-source world has quietly split into three Camps.
The LangChain Camp: langchain → langgraph → deepagents
The veteran. It started as a component library, grew into orchestration, and has now arrived at the batteries-included Deep Agents.
- Language: Python first, with JS/TS versions keeping pace.
- Ecosystem: the whole LangChain suite, plus LangSmith for observability and evals.
The Pi Camp: pi → oh-my-pi → flue
Everything revolves around pi, a minimal core, with the community building on top. oh-my-pi is a fork that goes the batteries-included route as a terminal coding agent. Flue, from the Astro team, uses pi as its foundation and turns it into a programmable, headless agent framework.
- Language: TypeScript.
- Ecosystem: community-driven, with a small core and plenty of extensions; Flue already runs on Cloudflare.
The AI SDK Camp: ai sdk → workflow → eve
Made by Vercel. The AI SDK handles model and tool calls, the Workflow SDK handles durable execution, and eve builds a Next.js-style agent framework on top.
- Language: TypeScript.
- Ecosystem: the Vercel platform, with AI Gateway, Sandbox and other infrastructure ready out of the box.
At a Glance
| LangChain Camp | Pi Camp | AI SDK Camp | |
|---|---|---|---|
| Main language | Python (plus JS/TS) | TypeScript | TypeScript |
| Foundation | LangChain | pi | AI SDK |
| Orchestration / durability | LangGraph | Left to the layers above | Workflow SDK |
| Out-of-the-box harness | Deep Agents | oh-my-pi, Flue | eve |
| Backed by | LangChain (the company) | Community + Astro team | Vercel |
| Deployment | Anywhere, paired with LangSmith | Anywhere; Flue runs on Cloudflare | Vercel first |
Finally
The three start from very different places: an established Python framework, a minimal community core, and a cloud platform. Yet their paths look strikingly alike: foundation → orchestration → an out-of-the-box harness.
The harness is shifting from a feature to the product itself. As for which one to pick and how to put it to use, I’ll leave that for you to ponder.