Pi is a minimal terminal coding harness that allows users to customize their workflows with extensions, skills, and themes. It supports multiple modes, including interactive, print/JSON, RPC, and SDK, and has a minimal system prompt that can be extended with custom providers and models. Pi is designed to be extensible and adaptable to different workflows, rather than dictating a specific workflow to the user. The article highlights Pi's features, such as its ability to rewind to prior messages, branch from there, and share the entire session with others.