What Is OpenAI Codex? The Complete History: From 2021 Code Model to Codex Sites (2026)
The complete history of OpenAI Codex: born in 2021, deprecated in 2023, reborn in 2025 as an agentic coding tool, and turned into an app builder with Codex Sites in June 2026. What it is, who can use it, and the open alternative.









