Pi

Most coding agents want you to live inside their product. Pi wants the opposite: it hands you a small, sharp core and gets out of the way, then lets you bolt on exactly the workflow you want. It is the first agent in a while that felt like a tool I owned rather than rented.

Pi is a minimal terminal coding harness — an open-source CLI agent from Earendil that reads files, writes code, and runs commands inside your real project directory. The pitch is restraint: instead of baking in a hundred features, it ships a tiny default toolset and makes everything else an extension you opt into. The result is an agent you can actually read, understand, and reshape.

What you actually get

The core is deliberately small, and that is the point:

• Four default tools. Read, write, edit, and bash — enough for the model to do real work, with nothing you have to fight.
• Skills and packages. Add capabilities — sub-agents, plan mode, permission gates, sandboxing, SSH execution — as TypeScript extensions shipped over npm or git. There are 50+ examples to crib from.
• 15+ model providers. Anthropic, OpenAI, Google, Bedrock, Mistral, Groq, xAI, OpenRouter, Ollama and more, switchable mid-session with /model.
• Four ways to run it. Interactive TUI, print/JSON output, an RPC protocol, and an SDK you can embed — so the same agent fits a chat session, a script, or your own app.
• Branching, shareable sessions. Tree-structured history with mid-session steering and custom compaction, so long tasks stay legible.

Where it shines

The minimalism is freeing. Because the core is so small, you can read what the agent is doing and trust it. Context engineering through AGENTS.md / SYSTEM.md plus automatic compaction means long sessions don't rot. And being model-agnostic is a genuine superpower: pin a cheap model for grunt work, swap to a frontier model for the hard step, all without leaving the session. For tinkerers, the extension model turns “I wish it did X” into a weekend afternoon.

Pi is the first coding agent in a while that felt like a tool I owned rather than one I rented.

Where it frustrates

That same minimalism is the cost. Out of the box Pi does less than a batteries-included rival — the good stuff lives in skills you have to find, install, or write, which means a real learning curve and a willingness to read TypeScript. There's no polished GUI and no hand-holding; this is a terminal-native tool for people comfortable there. If you want an agent that just works on day one with zero config, the assembly-required philosophy will feel like homework.

The verdict

Pi is open source under the MIT license and free to run — you only pay your model provider. That makes it an easy yes for the curious: there is no lock-in and no subscription to regret. It rewards people who want to understand and shape their tools, and it punishes people who want magic without setup. If you are the former, it is one of the most quietly exciting agents around.