Pi

Pi is an open-source coding agent that emphasizes minimalism and extensibility. It runs in the terminal with only four built-in tools (read, write, edit, and bash) and a system prompt of roughly 300 words, making it one of the leanest coding agents available.

Rather than bundling features like plan mode, to-do lists, or MCP support, Pi encourages users to extend its capabilities through TypeScript extensions, skills, or by asking the agent to build new functionality itself. Sessions are stored as tree structures, enabling branching and navigation without losing context.

Pi supports multiple LLM providers including Anthropic, OpenAI, Google, xAI, Groq, and others. It can authenticate via API keys or subscriptions like Claude Pro, ChatGPT Plus, or Gemini CLI.

Pi treats the context window as a scarce budget: by keeping the system prompt small, loading tools on demand, and avoiding hidden context injection, more of the window is available for actual code and project-specific information.

Official website: github.com/badlogic/pi-mono