Codex

OpenAI's agentic coding and work platform: a CLI (April 2025) plus a desktop app (built Nov 2025, released Feb 2026) built on the GPT-5-series Codex models, extended by skills/plugins, a headless App Server Protocol, and the Symphony orchestrator; the OpenAI-side reference harness paired against Claude Code, subject of the June 2026 'Shift to Agentic AI' study, and — per its product lead — an app ~90% of OpenAI's whole company uses that is spreading from code into general knowledge work