Prime Agent is an open-source, terminal-native AI coding and research agent built by PrimeIntellect-ai for general and long-running work, released under the MIT License. It was forked from pi-mono on 2026-05-08 and is now developed and distributed independently as the prime-agent CLI, installable via a custom R2-hosted tarball installer. Two architectural facts explain almost everything else: a persistent IPython kernel is the sole built-in tool substrate (with %%bash cells and Python skills replacing the legacy bash and edit built-ins), and a background daemon hosts multiple concurrent agent sessions in isolated worker processes that survive terminal disconnects.
Setup and installation covers first-run orientation, the monorepo build, the self-update protocol, and version-by-version upgrade notes — start here if you're installing or upgrading. Session runtime is the core reference for programmatic use: createAgentSession, AgentSessionRuntime, AgentSessionServices, kernel bootstrap, system prompt assembly, and the Settings schema. Tools, Skills and compaction, and Extensions document what the agent can do and how to extend it — the IPython tool, Bash tool, and Edit tool implementations; the Skills and Compaction subsystems; and the extension loader, UI context, and lifecycle API. Daemon architecture, Autonomous and ACP modes, and TUI and interactive use cover the run-time surfaces — the JSONL daemon protocol and mode implementation, autonomous mode with RLM subagents and long-running agents, ACP mode over NDJSON stdio, and the interactive TUI's sessions, navigation, and message queue. Providers and authentication and Testing and harness round out the tree with model-provider setup and the Test harness plus Continual Harness and refine machinery used for evaluation and self-improvement.
If you came here to install and run prime-agent for the first time, read Orientation and installation in the Setup and installation section, then Providers and authentication to log in to a model. If you came here to understand the architecture end-to-end, read Daemon architecture first for the client/supervisor/worker split, then Session runtime for what runs inside a worker, then Autonomous and ACP modes for how long-running and external-harness sessions are driven. If you came here to add a feature — a new tool, skill, or UI affordance — read Extensions for the loader and lifecycle, then the relevant page under Tools or Skills and compaction for the surface you're extending. If you came here to debug behavior or write tests, read Test harness and Continual Harness and refine under Testing and harness, and consult Upgrading under Setup and installation when old code or session artifacts reference removed names like RLMResult, the bare /resume flag, or the .pi/ config directory.