Pi

Pi is a minimal, open-source agent harness for building AI-powered coding assistants that adapt to the user's workflow rather than forcing a preset configuration. It supports 15+ providers including Anthropic, OpenAI, and Google with mid-session model switching, and is extensible via TypeScript extensions for custom commands, tools, workflows, and UI tweaks. Sessions are stored as branching trees exportable to HTML or shareable GitHub gists, with context engineering support for project instructions, skills, and prompt templates plus automatic message compaction. Pi runs in four modes — interactive TUI, print/JSON, RPC, and an embeddable SDK — with real-time steering to interrupt or redirect the agent mid-task.